blocks|key|798530|text|看看苹果开发者网站上的文档：https://developer.apple.com/library/prerelease/ios/#documentation/General/Conceptual/ARCProgrammingGuide/Introduction.html#//apple_ref/doc/uid/TP40011029|type|unstyled|depth|inlineStyleRanges|entityRanges|offset|length|data|798531|在页面底部有一个关于保留周期的部分。|798532|entityMap|0|LINK|mutability|MUTABLE|url|https://developer.apple.com/library/prerelease/ios/#documentation/General/Conceptual/ARCProgrammingGuide/Introduction.html#//apple_ref/doc/uid/TP40011029^0|E|49|0|0|0^^$0|@$1|2|3|4|5|6|7|N|8|@]|9|@$A|O|B|P|1|Q]]|C|$]]|$1|D|3|E|5|6|7|R|8|@]|9|@]|C|$]]|$1|F|3|-4|5|6|7|S|8|@]|9|@]|C|$]]]|G|$H|$5|I|J|K|C|$L|M]]]]

Take a look at the documentation on the Apple developer website : <a href="https://developer.apple.com/library/prerelease/ios/#documentation/General/Conceptual/ARCProgrammingGuide/Introduction.html#//apple_ref/doc/uid/TP40011029" rel="nofollow">https://developer.apple.com/library/prerelease/ios/#documentation/General/Conceptual/ARCProgrammingGuide/Introduction.html#//apple_ref/doc/uid/TP40011029</a>

There is a section about retain cycles at the bottom of the page.

blocks|key|798567|text|当我尝试Guillaume提供的解决方案时，在Debug模式下一切正常，但在Release模式下崩溃。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|798568|请注意，不要使用__weak而要使用__unsafe_unretained，因为我的目标是iOS+4.3。|798569|当在对象"+request“上调用setCompletionBlock:时，我的代码崩溃了:request被释放...|798570|因此，此解决方案在调试和发布模式下都有效：|798571|//+Avoiding+retain+cycle+:
//+-+ASIHttpRequest+object+is+a+strong+property+(crashs+if+local+variable)
//+-+use+of+an+__unsafe_unretained+pointer+towards+self+inside+block+code

self.request+=+[ASIHttpRequest+initWithURL:...
__unsafe_unretained+DataModel+*+dataModel+=+self;

[self.request+setCompletionBlock:%5E
{
++++[dataModel+processResponseWithData:dataModel.request.receivedData];++++++++
}];|code-block|syntax|javascript|798572|entityMap^0|0|0|0|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@]|9|@]|A|$]]|$1|D|3|E|5|6|7|Q|8|@]|9|@]|A|$]]|$1|F|3|G|5|6|7|R|8|@]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

When I try the solution provided by Guillaume, everything is fine in Debug mode but it crashs in Release mode.

Note that don't use __weak but __unsafe_unretained because my target is iOS 4.3.

My code crashs when setCompletionBlock: is called on object "request" : request was deallocated ...

So, this solution works both in Debug and Release modes :

<pre><code>// Avoiding retain cycle :
// - ASIHttpRequest object is a strong property (crashs if local variable)
// - use of an __unsafe_unretained pointer towards self inside block code

self.request = [ASIHttpRequest initWithURL:...
__unsafe_unretained DataModel * dataModel = self;

[self.request setCompletionBlock:^
{
 [dataModel processResponseWithData:dataModel.request.receivedData]; 
}];
</code></pre>

blocks|key|798594|text|ASIHTTPRequest+*request+=+[[ASIHTTPRequest+alloc]+initWithURL:...
__block+ASIHTTPRequest+*blockRequest+=+request;
[request+setCompletionBlock:%5E{
++++NSDictionary+*jsonDictionary+=+[[CJSONDeserializer+deserializer]+deserialize:blockRequest.responseData+error:nil];
++++blockRequest+=+nil;
//+....

}];|type|code-block|depth|inlineStyleRanges|entityRanges|data|syntax|javascript|798595|what+the+difference+between+__weak+and+__block+reference?|unstyled|offset|length|798596|entityMap|0|LINK|mutability|MUTABLE|url|https://stackoverflow.com/questions/11773342/what-the-difference-between-weak-and-block-reference^0|0|0|1L|0|0^^$0|@$1|2|3|4|5|6|7|Q|8|@]|9|@]|A|$B|C]]|$1|D|3|E|5|F|7|R|8|@]|9|@$G|S|H|T|1|U]]|A|$]]|$1|I|3|-4|5|F|7|V|8|@]|9|@]|A|$]]]|J|$K|$5|L|M|N|A|$O|P]]]]

<pre><code>ASIHTTPRequest *request = [[ASIHTTPRequest alloc] initWithURL:...
__block ASIHTTPRequest *blockRequest = request;
[request setCompletionBlock:^{
 NSDictionary *jsonDictionary = [[CJSONDeserializer deserializer] deserialize:blockRequest.responseData error:nil];
 blockRequest = nil;
// ....

}];
</code></pre>

<a href="https://stackoverflow.com/questions/11773342/what-the-difference-between-weak-and-block-reference">what the difference between __weak and __block reference?</a>

blocks|key|582616|text|它是由于将自我保留在方块中而造成的。block将从self访问，self在Block中引用。这将创建一个保留周期。|type|unstyled|depth|inlineStyleRanges|entityRanges|data|582617|尝试通过创建self的弱引用来解决此问题|offset|length|style|CODE|582618|__weak+typeof(self)+weakSelf+=+self;

operationManager+=+[[AFHTTPRequestOperation+alloc]+initWithRequest:request];
operationManager.responseSerializer+=+[AFJSONResponseSerializer+serializer];
[operationManager+setCompletionBlockWithSuccess:%5E(AFHTTPRequestOperation+*operation,+id+responseObject)+{

++++[weakSelf+requestFinishWithSucessResponseObject:responseObject+withAFHTTPRequestOperation:operation+andRequestType:eRequestType];

}+failure:%5E(AFHTTPRequestOperation+*operation,+NSError+*error)+{
++++[weakSelf+requestFinishWithFailureResponseObject:error+withAFHTTPRequestOperation:operation+andRequestType:eRequestType];
}];
[operationManager+start];|code-block|syntax|javascript|582619|entityMap^0|0|6|4|0|0^^$0|@$1|2|3|4|5|6|7|O|8|@]|9|@]|A|$]]|$1|B|3|C|5|6|7|P|8|@$D|Q|E|R|F|G]]|9|@]|A|$]]|$1|H|3|I|5|J|7|S|8|@]|9|@]|A|$K|L]]|$1|M|3|-4|5|6|7|T|8|@]|9|@]|A|$]]]|N|$]]

It causes due to retaining the self in the block. Block will accessed from self, and self is referred in block. this will create a retain cycle.

Try solving this by create a weak refernce of <code>self</code>

<pre><code>__weak typeof(self) weakSelf = self;

operationManager = [[AFHTTPRequestOperation alloc] initWithRequest:request];
operationManager.responseSerializer = [AFJSONResponseSerializer serializer];
[operationManager setCompletionBlockWithSuccess:^(AFHTTPRequestOperation *operation, id responseObject) {

 [weakSelf requestFinishWithSucessResponseObject:responseObject withAFHTTPRequestOperation:operation andRequestType:eRequestType];

} failure:^(AFHTTPRequestOperation *operation, NSError *error) {
 [weakSelf requestFinishWithFailureResponseObject:error withAFHTTPRequestOperation:operation andRequestType:eRequestType];
}];
[operationManager start];
</code></pre>

blocks|key|582681|text|有时候xcode编译器在标识保留周期时会出现问题，所以如果你确定你没有保留completionBlock，你可以像这样放一个编译器标志：|type|unstyled|depth|inlineStyleRanges|entityRanges|data|582682|#pragma+clang+diagnostic+push
#pragma+clang+diagnostic+ignored+"-Warc-retain-cycles"
#pragma+clang+diagnostic+ignored+"-Wgnu"

-(void)someMethod+{
}|code-block|syntax|javascript|582683|entityMap^0|0|0^^$0|@$1|2|3|4|5|6|7|I|8|@]|9|@]|A|$]]|$1|B|3|C|5|D|7|J|8|@]|9|@]|A|$E|F]]|$1|G|3|-4|5|6|7|K|8|@]|9|@]|A|$]]]|H|$]]

Some times the xcode compiler has problems for identifier the retain cycles, so if you are sure that you isn't retain the completionBlock you can put a compiler flag like this: 

<pre><code>#pragma clang diagnostic push
#pragma clang diagnostic ignored "-Warc-retain-cycles"
#pragma clang diagnostic ignored "-Wgnu"

-(void)someMethod {
}
</code></pre>

In ARC enabled code, how to fix a warning about a potential retain cycle, when using a block-based API?

The warning: 
<code>Capturing 'request' strongly in this block is likely to lead to a retain cycle</code>

produced by this snippet of code: 

<pre><code>ASIHTTPRequest *request = [[ASIHTTPRequest alloc] initWithURL:...

[request setCompletionBlock:^{
 NSDictionary *jsonDictionary = [[CJSONDeserializer deserializer] deserialize:request.rawResponseData error:nil];
 // ...
 }];
</code></pre>

Warning is linked to the use of the object <code>request</code> inside the block.

Fix warning "Capturing [an object] strongly in this block is likely to lead to a retain cycle" in ARC-enabled code

编译器

在启用ARC的代码中，当使用基于块的API时，如何修复有关潜在保留周期的警告？警告：Capturing 'request' strongly in this block is likely to lead to a retain cycle由这段代码产生：ASIHTTPRequest *request = [[ASIH...

问修复启用ARC的代码中“在此块中强烈捕获[对象]可能导致保留循环”的警告
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