iOS巅峰之block(由浅到深)详解

导语

不会使用block的iOS程序员，不是一个合格的程序员  
学会了block，你再也不想用繁琐的代理 
block没有你想象中的那么难，不要害怕，不要畏惧，勇敢尝试 

什么是block

block其实就是一个代码块，把你想要执行的代码封装在这个代码块里，等到需要的时候再去调用。那block是OC对象吗？答案是肯定的

笔者以英语3.9级的水平给大家翻译下，“block是一个OC对象，这意味着它能被添加到集合，比如NSArray、NSDictionary”

block的定义

1. block属性或变量 
   格式：返回值类型(^block名称)(参数列表) 

<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;">/*定义属性，block属性可以用strong修饰，也可以用copy修饰  有小伙伴留言说苹果官方建议用copy，笔者查了下文档,  确实是这样的，不过笔者未测试出copy与strong的区别，大家喜欢啥就用啥吧*/</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@property</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">nonatomic</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">strong</span>) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^myBlock)();<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//无参无返回值</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@property</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">nonatomic</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">strong</span>) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^myBlock1)(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//带参数</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@property</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">nonatomic</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">strong</span>) <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *(^myBlock2)(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *);<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//带参数与返回值</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//定义变量</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^myBlock)() = <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;">//无参无返回值</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^myBlock1)(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</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;">//带参数</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *(^myBlock2)(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</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;">//带参数与返回值</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><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.block被当做方法的参数  
格式：(block类型)参数名称

<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;">void</span>)test:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^)())testBlock<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//无惨无返回值</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)test1:(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^)(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *))testBlock<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//带参数</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)test2:(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *(^)(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *))testBlock<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//带参数与返回值</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></ul><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></ul>

3.使用typedef定义block

<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;">typedef</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^myBlock)(); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//以后就可以使用myBlock定义无参无返回值的block</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">typedef</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^myBlock1)(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//使用myBlock1定义参数类型为NSString的block</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">typedef</span> <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *(^myBlock2)(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *); <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//使用myBlock2定义参数类型为NSString，返回值也为NSString的block</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//定义属性</span> <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">@property</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">nonatomic</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">strong</span>) myBlock testBlock; <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//定义变量</span> myBlock testBlock = <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;">//当做参数</span> - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)test:(myBlock)testBlock;</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><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>

block的赋值

格式：block = ^返回值类型(参数列表){} 
1. 没有参数没有返回值

<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;">myBlock testBlock = ^<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</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;">"test"</span>); }； <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//没有返回值，void可以省略</span>myBlock testBlock1 = ^(){     <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;">"test1"</span>); }； <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//没有参数，小括号也可以省略</span> myBlock testBlock2 = ^{     <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;">"test2"</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></ul><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></ul>

2.有参数没有返回值

<code class="hljs axapta 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;">myBlock1 testBlock = ^<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(NSString *<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">str</span>) {      NSLog(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">str</span>);}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//省略void</span>myBlock1 testBlock = ^(NSString *<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">str</span>) {      NSLog(<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">str</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></ul><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></ul>

3.有参数有返回值

<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;">myBlock2 testBlock = ^<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *str) {     <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(str)     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> @<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"hi"</span>;}<span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//有返回值时也可以省略返回值类型</span> myBlock2 testBlock2 = ^(<span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSString</span> *str) {     <span class="hljs-built_in" style="color: rgb(102, 0, 102); box-sizing: border-box;">NSLog</span>(str)     <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">return</span> @<span class="hljs-string" style="color: rgb(0, 136, 0); box-sizing: border-box;">"hi"</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></ul><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>

实战

接下来，我们就结合一个实例程序，来看看block在实际开发中的简单使用 

本案例涉及到两个控制器与一个Person类

1. 联系人列表控制器：使用tableView展示联系人列表，称为A控制器
2. 新建联系人控制器：创建新的联系人对象，称为B控制器
3. Person：联系人，有两个属性，name与phoneNumber

任务需求：点击A控制器右上角“新建”按钮跳到B控制器，B控制器添加联系人后，点击“保存”按钮返回A控制器，并将新添加的联系人展示到列表中

问题来了，如何将B控制器中的数据传递给A控制器呢？

那还不简单，A控制器直接把联系人数组传递给B控制器，B控制器新建联系人后添加到数组中，然后返回A控制器，在A控制器的viewWillAppear方法中刷新表格就OK了。

方法可行，但是不得不说，相当low，B控制器是用来添加联系人的，至于联系人数组什么情况，无需关心，所以，不要把数组传递给B控制器

B控制器要做的仅仅只是，新建联系人，然后把联系人对象传递给A控制器，至于A控制器拿到联系人后会做什么，那是A的事情，与B无关

看到这里，很多人可能已经想到了代理，没错，代理也可以实现，但…是…，B控制器定义协议，声明代理方法，A控制器设置代理，遵守协议，然后实现代理方法，B控制器在合适的地方调用代理方法，卧槽，好麻烦有木有，笔者都不想写代码了，还是回家种田去吧

好了不废话了，进入正题

使用block传递数据

1. 在B控制器的.h文件中定义一个没有返回值，参数类型为Person的block属性

<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;">@property</span> (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">nonatomic</span>, <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">strong</span>) <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>(^saveBlock)(Person *);</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><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>

2.在B控制器“保存”按钮的点击方法中调用block

<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;"> - (IBAction)save:(id)sender {     <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//使用事先定义好的类方法创建Person对象</span>  Person *person = [Person personWithName:_nameText.text phoneNumber:_phoneNumberText.text];   <span class="hljs-javadoc" style="color: rgb(136, 0, 0); box-sizing: border-box;">/**调用block之前最好先判断block是否为空，不为空才调用，否则程序崩溃*/</span>   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//装逼写法</span> <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//!self.saveBlock? : self.saveBlock(person);</span>   <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//一般写法</span>   <span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">if</span> (self.saveBlock) {       self.seveBlock(person);   }  [self.navigationController popViewControllerAnimated:YES]; }</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></ul><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></ul>

3.在A控制器中，给B控制器的block属性进行赋值

<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;">//“新建”按钮点击执行的方法</span>   - (<span class="hljs-keyword" style="color: rgb(0, 0, 136); box-sizing: border-box;">void</span>)newContact {     AddContactViewController *addVC = [[AddContactViewController alloc] init];     addVC<span class="hljs-variable" style="color: rgb(102, 0, 102); box-sizing: border-box;">.saveBlock</span> = ^(Person *person){          <span class="hljs-comment" style="color: rgb(136, 0, 0); box-sizing: border-box;">//这里就可以拿到B控制器传递过来的person对象，添加到数组然后刷新表格</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;">.contactList</span> addObject:person];      [<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;">.tableView</span> reloadData];     };     [<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;">.navigationController</span> pushViewController:addVC animated:<span class="hljs-literal" style="color: rgb(0, 102, 102); box-sizing: border-box;">YES</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><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>

三步就搞定，很简单是不是，所以说，block并没有你们想想的那么复杂，自从笔者学会了block，就再也没用过代理，除了系统的。

block常见雷区—循环引用

使用block有一个特别要注意的地方，循环引用，何为循环引用？你引用我，我引用你，谁也不释放谁，对象无法销毁，占用内存

我们来看一个循环引用的一个例子 

注意看控制台输出，当点击“取消”时，B控制器被销毁，dealloc方法被调用

把注释掉的代码打开，再运行 

点击“取消”按钮，B被移除，但是dealloc方法没有调用，所以说，B控制器并没有销毁，why？

block对象赋值给了B控制器的属性，因此B会对block有一个强引用，而block中又用到了self（B控制器对象），block会对使用到的外部变量进行捕获，所以，block对B控制器也有一个强引用，最终造成循环引用，谁也无法释放

循环引用解决方法

循环引用如何解决？很简单，一行代码搞定

使用weakSelf（名称随便取的）替代self，block将不再对self进行强引用 
图中__weak也可使用__unsafe_unretained，区别就是__weak修饰的指针，当对象销毁后，指针会被自动置为nil，而__unsafe_unretained修饰的指针，当对象销毁后会变成野指针，为了安全，推荐使用__weak

block的分类

block可分为三种

• NSStackBlock：栈block
• NSMallocBlock：堆block
• NSGlobalBlock：全局block

1. 栈block 
   特点：生命周期由系统控制，函数返回即销毁 
   用到局部变量、成员属性变量，且没有强指针引用的block都是栈block

a.用到局部变量（图1），i为局部变量，block直接在NSLog中打印，没有被指针引用 

b.用到成员属性变量（图2），name为成员属性 

2.堆block 
特点：没有强指针引用即销毁，生命周期由程序员手动管理 
栈block如果有强指针引用或copy修饰的成员属性引用就会被拷贝到堆中，变成堆block

a.强指针引用（图3），block被testBlock引用，testBlock就是一个block类型的强指针（ARC环境下默认就是强指针） 

b.copy修饰的成员属性引用（图4） 

3.全局block 
特点：命长，有多长？很长很长，人在塔在（应用程序在它就在） 
没有用到外界变量，或者只用到全局变量、静态(static)变量的block就是全局block

对于全局block，有没有指针引用都不影响，block类型的成员属性无论是用assign、weak、strong还是copy修饰都无所谓，不过开发中很少用到全局block，所以不要用weak或assign

a.没有用到外界变量（图5），下图中block没有用到外界变量，所以就算用weak修饰也是全局block（举个例子而已，开发中不要用weak，用了也别说是笔者教的） 

b.只用到全局变量、静态(static)变量（图6），str为全局变量，str1为静态变量，只用到其中一个也是全局block 

分类总结 
1.没有用到外界变量或只用到全局变量、静态变量的block为全局block，生命周期从创建到应用程序结束 
2.用到局部变量、成员属性变量的block为栈block，生命周期系统控制，函数返回即销毁 
3.有强指针引用或copy修饰的成员属性引用的block会被复制一份到堆中成为堆block，没有强指针引用即销毁，生命周期由程序员控制

block对外界变量的捕获

a.基本数据类型—局部变量 
block会拷贝该变量的值当做常量使用，外界修改变量的值不会影响block内部，且block内部不能对其修改

block内部修改外界变量i的值直接报错，如果想要修改，可以在int i = 0前面加上关键字__block，此时i等效于全局变量或静态变量 

外界变量i从0变成了1，block内部打印依然是0 

b.基本数据类型—静态变量、全局变量、成员属性变量 
block直接访问变量地址，在block内部可以修改变量的值，并且外部变量被修改后，block内部也会跟着变

图中_k为成员属性变量，初始值i = 10，j = 20，k = 0，block内部只对i、j、k进行一次自增操作，打印结果却是i = 12，j = 22，k = 2，所以外部的自增操作也影响了内部，即访问的是同一个内存地址 

c.指针类型—局部变量 
block会复制一份指针并强引用指针所指对象，且内部不能修改指针的指向

图中被注释掉的代码试图修改指针指向，所以会报错（如果想要修改，在前面加上__block），但是可以修改所指对象的值，如str从“abc”变成了“abcdef” 

d.指针类型—全局变量、静态变量、成员变量属性 
block不会复制指针，但是会强引用该对象，内部可修改指针指向，block会强引用成员属性变量所属的对象，这也是为什么block属性内部用到self.xxx会引起循环引用的原因

图中str2为成员属性，由于NSString是不可变的，所以从打印结果可以看出，在block内部修改了外界指针变量的引用，指向了新的字符串 

转自：http://ios.jobbole.com/84127/