OC 设计模式

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单例模式

单例简介

单例是生命周期与程序生命周期相同，仅能生成一次、且不能被销毁的唯一实例；
需要确保应用中的一个特定类有且仅有一个实例（对象）；
单例可在程序任何位置被访问，且一直存在；
单例实例获取方法命名规则：一般以standard…、shared…、default….开头；
单例必须至少满足以下条件：
- 只初始化一次；
- 全局存在；
- 唯一，对象不可改；
- 方便获取，任何位置可访问

系统单例

UIApplication：应用程序单例
NSNotificationCenter：通知中心单例
NSUserDefaults：用户默认单例
NSFileManager：文件管理单例

单例优点

共享信息；
实例控制：Singleton会阻止其他对象实例化其自己的Singleton对象的副本，从而确保所有对象都访问唯一实例；
灵活性：因为类控制了实例化过程，所以类可以更加灵活地修改实例化过程；

自定义单例创建常用方法

首先创建一个继承于NSObject的类Singleton，其次在Singleton.m文件中实现如下代码；

方法1：一般创建

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;">"Singleton.h"</span></span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 静态变量保证单例对象始终存在</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> Singleton *singleton = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>;<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@implementation</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Singleton</span></span>+ (instancetype)defaultSingleton {    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 仅在单例对象为空时初始化一次，之后直接返回唯一的单例对象</span>    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (singleton == <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>) {        singleton = [[Singleton alloc] init];    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> singleton;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@end</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li></ul>

方法2：GCD创建（推荐使用）

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;">"Singleton.h"</span></span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> Singleton *singleton = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>;<span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@implementation</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Singleton</span></span>+ (instancetype)defaultSingleton {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once_t</span> onceToken;    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">dispatch_once</span>(&onceToken, ^{        singleton = [[Singleton alloc] init];    });    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> singleton;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@end</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>

自定义单例创建完整方法

一般创建单例方法可能会出现一些问题，我们通过不同的途径得到不同的对象，显然是不行的。我们必须要确保对象的唯一性，所以我们就需要封锁用户通过alloc/init/copy以及release/retain等方法来构造或操作对象这条道路。
我们知道，创建对象的步骤分为申请内存(alloc)、初始化(init)这两个步骤，我们要确保对象的唯一性，因此在第一步这个阶段我们就要拦截它。当我们调用alloc方法时，oc内部会调用allocWithZone这个方法来申请内存，我们覆写这个方法，然后在这个方法中调用defaultSingleton方法返回单例对象，这样就可以达到我们的目的。拷贝对象也是同样的原理，覆写copyWithZone方法，注意需遵守<NSCopying>协议，然后在这个方法中调用defaultSingleton方法返回单例对象，其他示例直接参考如下代码：

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">static</span> Singleton *singleton = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>;+ (instancetype)defaultSingleton {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!singleton) {        singleton = [[Singleton alloc] init];    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> singleton;}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// alloc</span>+ (instancetype)allocWithZone:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">struct</span> _NSZone *)zone {    @synchronized(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>) {        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (!singleton) {            singleton = [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> allocWithZone:zone];            <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> singleton;        }        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>;    }}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// copy</span>- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)copyWithZone:(NSZone *)zone {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>;}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// retain</span>- (instancetype)retain {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>;}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// release</span>- (oneway <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)release {}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// autorelease</span>- (instancetype)autorelease {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>;}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// retainCount</span>- (NSUInteger)retainCount {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> NSUIntegerMax;}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li><li style="box-sizing: border-box; padding: 0px 5px;">37</li><li style="box-sizing: border-box; padding: 0px 5px;">38</li><li style="box-sizing: border-box; padding: 0px 5px;">39</li><li style="box-sizing: border-box; padding: 0px 5px;">40</li><li style="box-sizing: border-box; padding: 0px 5px;">41</li><li style="box-sizing: border-box; padding: 0px 5px;">42</li><li style="box-sizing: border-box; padding: 0px 5px;">43</li><li style="box-sizing: border-box; padding: 0px 5px;">44</li><li style="box-sizing: border-box; padding: 0px 5px;">45</li><li style="box-sizing: border-box; padding: 0px 5px;">46</li><li style="box-sizing: border-box; padding: 0px 5px;">47</li><li style="box-sizing: border-box; padding: 0px 5px;">48</li></ul>

单例使用

首先在main.m文件中，引入“Singleton.h”，其次创建两个单例实例，并且打印对象信息；

这里写图片描述

我们可以看到，两个实例对象的地址是一致的，由此可见，单例的唯一性。

可利用单例的唯一性进行传值，但必须满足一个前提条件就是，在传值时，必须保证单例存在并且单例属性确实有值。

现在在Singleton.h文件中声明属性name，其次创建一个Person类，为其设置属性name，并且重写init方法，通过单例对name直接复制，如下所示：

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;">"Person.h"</span></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;">"Singleton.h"</span></span><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@implementation</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">Person</span></span>- (instancetype)init {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> = [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> init];    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>) {        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 获取单例属性值赋给name</span>        <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span><span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.name</span> = [Singleton defaultSingleton]<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.name</span>;    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>;}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@end</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li></ul>

切换到main.m文件中，创建单例实例，并且给name属性复制，其次实例化Person对象，并打印person.name，如下所示：

<code class="hljs vala has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <Foundation/Foundation.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import "Singleton.h"</span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import "Person.h"</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> * argv[]) {    @autoreleasepool {<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#pragma mark - 单例模式</span>        Singleton *singleton = [Singleton defaultSingleton];        singleton.name = @<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Admin"</span>;        Person *person = [[Person alloc] init];        NSLog(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Person's name is '%@'."</span>, person.name); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//  Person's name is 'Admin'.</span>    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li></ul>

从上述代码中可以看出，可通过单例进行传值操作。

KVC 键值编码

概述

KVC是KeyValueCoding的简称，它是一种可以直接通过字符串的名字(key)来访问类属性(实例变量)的机制。而不是通过调用Setter、Getter方法访问。通常我们使用valueForKey来替代getter() 方法，setValue:forKey来代替setter()方法。
当使用KVO、Core Data、CocoaBindings、AppleScript(Mac支持)时，KVC是关键技术。

常用方法

取值方法

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1、</span>valueForKey:，传入<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span>属性的名字。<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2、</span>valueForKeyPath:，传入<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span>属性的路径，xx<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.xx</span>形式。</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li></ul>

设值方法

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1、</span>- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setValue:(nullable <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)value forKey:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)key;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2、</span>- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setValue:(nullable <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)value forKeyPath:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)keyPath;<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 3、- (void)setValuesForKeysWithDictionary:(NSDictionary<NSString *, id> *)keyedValues;</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 4、</span>- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)setValue:(nullable <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)value forUndefinedKey:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)key;</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

KVC 读取方式

KVC使用起来比较简单，但是它如何查找一个属性进行读取呢？具体查找规则（假设现在要利用KVC对name进行读取）：

如果是动态设置属性，则优先考虑调用setName方法，如果没有该方法则优先考虑搜索成员变量_name,如果仍然不存在则搜索成员变量name，如果最后仍然没搜索到则会调用这个类的setValue:forUndefinedKey：方法(注意搜索过程中不管这些方法、成员变量是私有的还是公共的都能正确设置)；
如果是动态读取属性，则优先考虑调用name方法（属性name的getter方法），如果没有搜索到则会优先搜索成员变量_name，如果仍然不存在则搜索成员变量name，如果最后仍然没搜索到则会调用这个类的valueforUndefinedKey:方法(注意搜索过程中不管这些方法、成员变量是私有的还是公共的都能正确读取)；

案例

1、声明 KVCClass 类，并在其.h文件中声明几个全局变量，无需定义成属性及生成存（setter）取（getter）方法，代码如下：

<code class="hljs java has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">#<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> <Foundation/Foundation.h><span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@interface</span> KVCClass : NSObject {    NSString *_name;        <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**< 姓名 */</span>    NSString *_nationality; <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**< 国籍 */</span>    NSInteger _age;         <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**< 年龄 */</span>}<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@end</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

2、在 “KVCClass.m”文件中，重写description方法与dealloc方法，代码如下：

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;">"KVCClass.h"</span></span><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@implementation</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">KVCClass</span></span>- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)dealloc {    [_name release]; _name = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>;    [_nationality release]; _nationality = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>;    [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> dealloc];}- (<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)description {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> stringWithFormat:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"<%p name:%@, age:%ld, address:%@>"</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>, _name, _age, _nationality];}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@end</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li></ul>

3、在main.m文件中，导入KVCClass.h，实例化对象，并通过KVC为其设值，代码如下：

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;"><Foundation/Foundation.h></span></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;">"KVCClass.h"</span></span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> * argv[]) {    @autoreleasepool {<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#pragma mark - KVC </span>        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1、逐一赋值</span>        KVCClass *kvcObject1 = [[KVCClass alloc] init];        [kvcObject1 setValue:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Charles"</span> forKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>];        [kvcObject1 setValue:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"China"</span> forKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"nationality"</span>];        [kvcObject1 setValue:@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">22</span> forKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"age"</span>];        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@"</span>, kvcObject1);        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 取值</span>        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Name is '%@'."</span>, [kvcObject1 valueForKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>]);        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2、统一赋值</span>        KVCClass *kvcObject2 = [[KVCClass alloc] init];        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSDictionary</span> *dic = @{@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"William"</span>, @<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"nationality"</span>:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"USA"</span>, @<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"age"</span>:@<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">30</span>};        [kvcObject2 setValuesForKeysWithDictionary:dic];        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@"</span>, kvcObject2);        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 取值</span>        <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Name is '%@'."</span>, [kvcObject2 valueForKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>]);    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li><li style="box-sizing: border-box; padding: 0px 5px;">31</li><li style="box-sizing: border-box; padding: 0px 5px;">32</li><li style="box-sizing: border-box; padding: 0px 5px;">33</li><li style="box-sizing: border-box; padding: 0px 5px;">34</li><li style="box-sizing: border-box; padding: 0px 5px;">35</li><li style="box-sizing: border-box; padding: 0px 5px;">36</li></ul>

控制台输出情况如下：

这里写图片描述

Tips
1、key的值必须正确，如果拼写错误，会出现异常；
2、当key的值是没有定义的，valueForUndefinedKey:这个方法会被调用，如果你自己写了这个方法，key的值出错就会调用到这里来；
3、因为类key反复嵌套，所以有个keyPath的概念，keyPath就是用.号来把一个一个key链接起来，这样就可以根据这个路径访问下去；
4、NSArray／NSSet等都支持KVC；

KVO 键值监听

概述

KVO,即：Key-Value Observing，它提供一种机制，当指定的对象的属性被修改后，则对象就会接受到通知。简单的说就是每次指定的被观察的对象的属性被修改后，KVO就会自动通知相应的观察者了。在ObjC中要实现KVO则必须实现NSKeyValueObServing协议，不过幸运的是NSObject已经实现了该协议，因此几乎所有的ObjC对象都可以使用KVO。
在面对对象编程时，我们很多情况下直接处理某些事件会很麻烦。如常见的程序运行中电话呼入、用户突然点击home键等等，一般我们使用观察者（代理）来处理类似事件。
在使用这些模式的时候，我们需要告诉这些角色，谁来响应这些事件，这就需要使用类的引用。
类的引用本质上就是如何让另外一个角色，“知道”另外一个角色，对应到代码中，就是如何让某一个类的对象，顺利的把信息传递给另外一个对象。
处理类的引用的时候，应注意以下几点：
- 每个类是否能正常接收到信息（响应动作）
- 信息传递时接收者是否存在
- 每个类是否能正常释放（不会引起循环引用）

键值观察

键值观察是基于键值编码的一种技术；
利用键值观察可以注册成为一个对象的观察者，在该对象的某个属性变化时收到通知；
被观察对象需要编写复合KVC标准的存取方法；

常用方法

系统框架已经支持KVO，所以程序员在使用的时候非常简单。

1、注册指定Key路径的监听器：addObserver: forKeyPath: options: context:

2、实现回调方法： observeValueForKeyPath: ofObject: change: context:

3、删除指定Key路径的监听器：removeObserver: forKeyPath、removeObserver: forKeyPath: context:

案例

此案例将KVC与KVO结合使用

1、声明 KVOClass 类，并在其.h文件中声明全局变量_weather；

<code class="hljs java has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">#<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">import</span> <Foundation/Foundation.h><span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@interface</span> KVOClass : NSObject {    NSString *_weather; <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**< 天气 */</span>}<span class="hljs-annotation" style="color: rgb(155, 133, 157); box-sizing: border-box;">@end</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

2、在“person.m”文件中实现如下代码：

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <span class="hljs-title" style="box-sizing: border-box;">"KVOClass.h"</span></span><span class="hljs-class" style="box-sizing: border-box;"><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@implementation</span> <span class="hljs-title" style="box-sizing: border-box; color: rgb(102, 0, 102);">KVOClass</span></span>- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)dealloc {    <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 移除监听</span>    [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> removeObserver:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> forKeyPath:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"weather"</span>];    [_weather release]; _weather = <span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>;    [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> dealloc];}- (instancetype)init {    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> = [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">super</span> init];    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>) {        <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 注册监听</span>        [<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> addObserver:<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span> forKeyPath:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"weather"</span> options:NSKeyValueObservingOptionNew|NSKeyValueObservingOptionOld context:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">nil</span>];    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">self</span>;}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 实现监听回调方法</span>- (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)observeValueForKeyPath:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *)keyPath ofObject:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>)object change:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSDictionary</span><<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *,<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">id</span>> *)change context:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span> *)context {    <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"天气发生变化，此时天气情况：%@"</span>, change[@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"new"</span>]);}<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@end</span></code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li><li style="box-sizing: border-box; padding: 0px 5px;">19</li><li style="box-sizing: border-box; padding: 0px 5px;">20</li><li style="box-sizing: border-box; padding: 0px 5px;">21</li><li style="box-sizing: border-box; padding: 0px 5px;">22</li><li style="box-sizing: border-box; padding: 0px 5px;">23</li><li style="box-sizing: border-box; padding: 0px 5px;">24</li><li style="box-sizing: border-box; padding: 0px 5px;">25</li><li style="box-sizing: border-box; padding: 0px 5px;">26</li><li style="box-sizing: border-box; padding: 0px 5px;">27</li><li style="box-sizing: border-box; padding: 0px 5px;">28</li><li style="box-sizing: border-box; padding: 0px 5px;">29</li><li style="box-sizing: border-box; padding: 0px 5px;">30</li></ul>

3、在“main.m”文件中导入KVOClass.h文件，实现如下代码，观察控制台：

<code class="hljs vala has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import <Foundation/Foundation.h></span><span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#import "KVOClass.h"</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> main(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">int</span> argc, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">const</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">char</span> * argv[]) {    @autoreleasepool {<span class="hljs-preprocessor" style="color: rgb(68, 68, 68); box-sizing: border-box;">#pragma mark - KVO</span>        KVOClass *kvoObject = [[KVOClass alloc] init];        [kvoObject setValue:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"晴"</span> forKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"weather"</span>];        [kvoObject release];    }    <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span>;}</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li><li style="box-sizing: border-box; padding: 0px 5px;">11</li><li style="box-sizing: border-box; padding: 0px 5px;">12</li><li style="box-sizing: border-box; padding: 0px 5px;">13</li><li style="box-sizing: border-box; padding: 0px 5px;">14</li><li style="box-sizing: border-box; padding: 0px 5px;">15</li><li style="box-sizing: border-box; padding: 0px 5px;">16</li><li style="box-sizing: border-box; padding: 0px 5px;">17</li><li style="box-sizing: border-box; padding: 0px 5px;">18</li></ul>

控制台输出：

<code class="hljs css has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;">2015<span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">-11-17</span> 23<span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:02</span><span class="hljs-pseudo" style="color: rgb(0, 0, 0); box-sizing: border-box;">:00</span><span class="hljs-class" style="box-sizing: border-box; color: rgb(155, 112, 63);">.860</span> <span class="hljs-tag" style="color: rgb(0, 0, 0); box-sizing: border-box;">DesignPatterns</span><span class="hljs-attr_selector" style="color: rgb(0, 136, 0); box-sizing: border-box;">[1392:132353]</span> 天气发生变化，此时天气情况：晴</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li></ul>

Tips
使用KVC可以大大地减少我们的代码量，当遇到property的时候，可以多想想是否可以KVC来帮助我，是否可以用KVC来重构代码，当需要加入observer模式时，可以考虑下KVO, 在高性能的observer里面，KVO会给我们很好的帮助。

数据持久化

iOS应用程序使用沙盒机制作为文件存储方式；
应用程序有一个独立的沙盒文件夹，程序仅能访问自己沙盒路径下的文件，任何情况下都无法访问其它程序的沙盒；
那我们可以通过什么方法将数据存入沙盒，同时也可以取出？可同 NSUserdefaults 或属性列表实现。
数据持久化的方法还有很多，如本地数据库（CoreData、sqlite、归档）、网络数据库（服务器）等等，会在后面的博客中介绍。

NSUserdefaults

常用方法

1、存值

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1、获取系统单例</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSUserDefaults</span> *defaults = [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSUserDefaults</span> standardUserDefaults];<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2、设值</span>[defaults setObject:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"William"</span> forKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>];<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 3、同步数据</span>[defaults synchronize];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

2、取值

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1、获取系统单例</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSUserDefaults</span> *defaults = [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSUserDefaults</span> standardUserDefaults];<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2、取值</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *name = [defaults objectForKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>];<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 3、打印信息</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Name is '%@'."</span>, name);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li></ul>

3、移除值

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1、获取系统单例</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSUserDefaults</span> *defaults = [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSUserDefaults</span> standardUserDefaults];<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2、删除值</span>[defaults removeObjectForKey:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"name"</span>];<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 3、同步数据</span>[defaults synchronize];</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li></ul>

Tips
1、从上述示例中可以看出，无论是什么操作，都需获取userdefaults单例，如果是存值或删除值，一定记得调用synchronize方法，同步数据。
2、通过userdefaults同样可以进行值的传递，因为userdefaults本质也是单例。

读写文件

我们可以自己通过代码，根据一条路径自动在桌面上创建一个文件，来存取我们的数据，注意：这个数据并非存在沙河中。

获取桌面文件路径方式：直接将桌面文件拖入Xcode工程即可，Xcode会自动获取文件路径。

<code class="hljs objectivec has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSDictionary</span> *dict = @{@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"account"</span>:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"Admin"</span>, @<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"password"</span>:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"123456"</span>};<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 1、写入文件</span><span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 将 dict 存入文件，/infomation.text 为自己给存储对象文件的命名</span>[dict writeToFile:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"/Users/LiHongyao/Desktop/Datas/infomation.text"</span> atomically:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">YES</span>];<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">// 2、读取文件</span><span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSDictionary</span> *infomation = [<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSDictionary</span> dictionaryWithContentsOfFile:@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"/Users/LiHongyao/Desktop/Datas/infomation.text"</span>];<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(@<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"%@"</span>, infomation);</code><ul class="pre-numbering" style="box-sizing: border-box; position: absolute; width: 50px; background-color: rgb(238, 238, 238); top: 0px; left: 0px; margin: 0px; padding: 6px 0px 40px; border-right-width: 1px; border-right-style: solid; border-right-color: rgb(221, 221, 221); list-style: none; text-align: right;"><li style="box-sizing: border-box; padding: 0px 5px;">1</li><li style="box-sizing: border-box; padding: 0px 5px;">2</li><li style="box-sizing: border-box; padding: 0px 5px;">3</li><li style="box-sizing: border-box; padding: 0px 5px;">4</li><li style="box-sizing: border-box; padding: 0px 5px;">5</li><li style="box-sizing: border-box; padding: 0px 5px;">6</li><li style="box-sizing: border-box; padding: 0px 5px;">7</li><li style="box-sizing: border-box; padding: 0px 5px;">8</li><li style="box-sizing: border-box; padding: 0px 5px;">9</li><li style="box-sizing: border-box; padding: 0px 5px;">10</li></ul>

输出情况：

<code class="hljs delphi has-numbering" style="display: block; padding: 0px; background-color: transparent; color: inherit; box-sizing: border-box; font-family: 'Source Code Pro', monospace;font-size:undefined; white-space: pre; border-top-left-radius: 0px; border-top-right-radius: 0px; border-bottom-right-radius: 0px; border-bottom-left-radius: 0px; word-wrap: normal; background-position: initial initial; background-repeat: initial initial;"><span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">2015</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">11</span>-<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">17</span> <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">23</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">49</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">39.302</span> DesignPatterns[<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">1562</span>:<span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">170884</span>] <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">{    account = Admin;    password = 123456;}</span><span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">Program</span> ended <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">with</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">exit</span> code: <span class="hljs-number" style="color: rgb(0, 102, 102); box-sizing: border-box;">0</span></code>

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