iOS开发之回调delegate的方法时判断delegate是否已经被释放
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最近的项目遇到了网络请求,需要在请求完成后回调delegate的方法。然而回调时经常遇到这种情况:delegate已经被释放,这时调用其方法则会引起crash。
objc的runtime中有两种判断类型的方式比较靠谱,他们可以直接取得任意一个objc_object(和id是完全一样的数据类型)的类或者类名。其函数如下:
//Returns the class name of a given object.const char *object_getClassName(id obj); //Returns the class of an object.Class object_getClass(id object);
第一个函数可以返回任意一个id的类名,第二个函数可以返回任意一个id的Class。这两个函数各有优劣。使用第一个函数判断类型是否改变的优点是在 iphone开发环境下默认公开,可以随便调用,缺点是要使用几字节的内存空间用于存放字符串,而且做字符串比较要稍微多花费一些CPU时间。第二个函数 优点是可以将获取的Class指针做为int型保存起来,只需要4字节,且比较起来节约CPU时间,坏处是我们要手动声明一下此函数才可以在自己的代码里 使用,否则会出现一个warning,提示“Implicit declaration of function ‘object_getClass’ is invalid in C99”,不过手动声明一下只要加一行代码就可以,也不麻烦。
下面是一个实例:
// WebService.h#import <Foundation/Foundation.h>@protocol ServiceDelegate;@interface WebService : NSObject { id <ServiceDelegate> _myDelegate; Class _originalClass;}@property (nonatomic, assign) id myDelegate;- (void)postDataWithURL:(NSString *)myURL postData:(NSDictionary *)dataDic setDelegate:(id)theDelegate;- (void)serviceFun:(NSDictionary *)paramDic;@end@protocol ServiceDelegate <NSObject>- (void)serviceCallBack:(id)resultObject serviceFlag:(NSInteger)flag;@end
// WebService.m#import "WebService.h"Class object_getClass(id object);@implementation WebService@synthesize myDelegate = _myDelegate;- (void)postDataWithURL:(NSString *)myURL postData:(NSDictionary *)dataDic setDelegate:(id)theDelegate{ self.myDelegate = theDelegate; _originalClass = object_getClass(theDelegate); [NSThread detachNewThreadSelector:@selector(serviceFun:) toTarget:self withObject:dataDic];}- (void)serviceFun:(NSDictionary *)paramDic{ Class currentClass = object_getClass(self.myDelegate); if (currentClass == _originalClass) { // 如果delegate没有被释放 }}
第二种方法
http://pingguohe.net/2011/09/01/howtojudgewhetheradelegateisreleased/#comment-983
困惑了相当长时间的一个问题了,实际上在Xcode4中会出现
if ((int)delegate->isa == classIsa) {
这行报错,member reference base type 'id<HTTPRequestDelegate>' is not a structure or union
因为ide不认为它是NSObject对象,只要对它转为NSObject对象即可。
//************************************************************************************
Cocoa中回调delegate的方法时判断delegate是否已经被释放
这个需要是因为最近在做网络请求的底层,需要在请求完成时回调某delegate的某方法。
然而回调时经常遇到这种情况:delegate已经被release了。如果delegate已经被dealloc掉,则无法调用其方法,否则引起程序crash。此篇文章中博客作者也有相同的问题:http://longtimenoc.com/archives/objective-c-delegate的那些事儿
首先,我们此时无法用if (nil = delegate)判断delegate是否已经被dealloc掉,因为被dealloc之后,delegate对象也不是空的,大部分情况下是一个objc_object*类型的C指针。
其次,我们又会想到在本对象中先对delegate retain一次,这样回调时不会崩溃了。但是这样会出现一个retain cycle,本对象和delegate都永远不会被释放了。
再次,我想到是否可以用isKindOfClass判断是否被dealloc。然而此时也不能用[delegate isKindOfClass]判断是否已经被dealloc,因为isKindOfClass是NSObject协议中的方法,此时delegate如果不是NSObject,对其发送isKindOfClass消息会导致crash。
此时很小部分情况下,delegate会是NSObject,可能是NSDictioary,也可能是原本的类。而大部分情况下,delegate已经不是NSObject。所以此时任何形式的[delegate method]都会导致crash,因为任何的[delegate method]的前提都是:delegate是一个NSObject。
无奈之下我又想到,使用delegate->isa判断delegate是不是NSObject。这里介绍一下,objective-c中所有对象都是结构体,每个结构体中都有一个名为isa的指针指向其类。而类也是一种结构体,类的isa指向其父类。处于最底层的结构体是无isa的,NSObject的isa指向的也是NSObject。isa具体的值是运行时确定的。
一开始的思路是用delegate->isa->isa->isa->…一直指下去,如果isa与NSObject的isa相同,则说明delegate是一个NSObject。但是这样是行不通的,因为如果delegate不是NSObject,只是objc_object*,一直指下去却指不到NSObject的话,总会指到最底层的结构体,而此结构体无isa,如果访问结构体内没有的东西,程序又会crash了。说了这么多,结论就是这个问题很是蛋疼。再做不出来我就要把释放本对象的责任交给用户了。
等等,如果在本对象初始化后,delegate传进来时保存delegate的isa,此时delegate一定未被dealloc(为什么?因为是单线程的),在回调时判断delegate此时的isa和当时保存的isa是否一样,就可以解决了。
代码如下:
协议声明:
- @protocol HTTPRequestDelegate <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px"><</span>NSObject<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">></span>
- @optional
- <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">-</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(153,51,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">void</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span> requestDidLoadResponse<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">:</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span>NSString <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">*</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>responseDictionary<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">-</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(153,51,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">void</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span> requestDidFailedLoadResourceURLWithError<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">:</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span>NSError <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">*</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>error<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- @end
类声明:
- @interface MyClass <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">:</span> NSObject <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px"><</span>FooDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">,</span>BarDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">></span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">{</span>
- ...
- <span style="color:rgb(153,51,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">int</span> classIsa<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- id <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px"><</span>HTTPRequestDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">></span> delegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">}</span>
- @property <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span>nonatomic<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">,</span>assign<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span> id <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px"><</span>HTTPRequestDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">></span> delegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- @end
类实现:
- @implementation MyClass
- @synthesize delegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">-</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span>id<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>initWithDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">:</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span>id<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>requestDelegate
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">{</span>
- self <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">=</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">[</span>super init<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">]</span><span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(177,177,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">if</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span>self<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">{</span>
- <span style="color:rgb(102,102,102); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px"><em>//TODO:Send request,etc.</em></span>
- self.<span style="color:rgb(32,32,32); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">delegate</span> <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">=</span> requestDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">}</span>
- <span style="color:rgb(177,177,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">return</span> self<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">}</span>
- <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">-</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(153,51,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">void</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>setDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">:</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span>id<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px"><</span>HTTPRequestDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">></span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>iDelegate
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">{</span>
- delegate <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">=</span> iDelegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- NSString <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">*</span>delegateDescription <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">=</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">[</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">[</span>iDelegate class<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">]</span> description<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">]</span><span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- classIsa <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">=</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(153,51,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">int</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>objc_getClass<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">[</span>delegateDescription UTF8String<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">]</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span><span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">}</span>
- <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">-</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(153,51,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">void</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>callback
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">{</span>
- <span style="color:rgb(177,177,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">if</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(153,51,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">int</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span>delegate<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">-></span>isa <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">==</span> classIsa<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">{</span>
- <span style="color:rgb(177,177,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">if</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">[</span>delegate respondsToSelector<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">:</span>@selector<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">(</span>requestDidLoadResponse<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">:</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">]</span><span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">)</span> <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">{</span>
- NSString <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">*</span>responseString <span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">=</span> @<span style="color:rgb(255,0,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">"foobar"</span><span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">[</span>delegate requestDidLoadResponse<span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">:</span>responseString<span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">]</span><span style="color:rgb(51,153,51); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">;</span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">}</span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">}</span>
- <span style="color:rgb(0,153,0); padding-top:0px; padding-right:0px; padding-bottom:0px; padding-left:0px; margin-top:0px; margin-right:0px; margin-bottom:0px; margin-left:0px">}</span>
然而由于多线程的原因(发出请求和回调发生是在两个线程上的),会有极少数的情况(测试中发生概率在万分之一以内,和CPU有关)在if ((int)delegate->isa == classIsa)判断时,delegate当前的isa会和本对象初始化时isa相等,也就是说delegate未被dealloc,而调用回调时,delegate已被dealloc,导致程序crash。避免这种小概率事件的方法是,在delegate中发送请求前[self retain]一下,然后在回调到达时[self release]一下,这样除了避免崩溃以外,还会确保请求已经发送完毕,不会被发送一半。
以上。
–OpenThread
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