修复警告“在该块中强烈捕获[对象]可能导致保留周期”在启用ARC的代码中 [英] Fix warning "Capturing [an object] strongly in this block is likely to lead to a retain cycle" in ARC-enabled code

问题描述

在启用ARC的代码中，如何在使用基于块的API时修复关于潜在保留周期的警告？

警告：

在此块中强烈捕获请求可能导致此代码段生成的保留周期

代码：

  ASIHTTPRequest * request = [[ASIHTTPRequest alloc] initWithURL：... 
 
 [请求setCompletionBlock：^ {
 NSDictionary * jsonDictionary = [[CJSONDeserializer deserializer] deserialize：request.rawResponseData error：nil]; 
 // ... 
}]; 
  

警告与对象的使用请求






= 我对文档的理解说，在块中使用关键字 block 后将变量设置为nil应该可以，但它仍然显示警告。

  __ block ASIHTTPRequest * request = [[ASIHTTPRequest alloc] initWithURL：... 
 
 [request setCompletionBlock：^ {
 NSDictionary * jsonDictionary = [[CJSONDeserializer deserializer] deserialize：request.responseData error：nil]; 
 request = nil; 
 // .... 
 
}]; 
  

更新：使用关键字'_ < weak'而不是' _block'，并使用一个临时变量：

  ASIHTTPRequest * _request = [[ASIHTTPRequest alloc ] initWithURL：... 
 __weak ASIHTTPRequest * request = _request; 
 
 [request setCompletionBlock：^ {
 NSDictionary * jsonDictionary = [[CJSONDeserializer deserializer] deserialize：request.responseData error：nil]; 
 // ... 
}]; 
  

如果您还要定位iOS 4，请使用 __ unsafe_unretained ，而不是 __ weak 。同样的行为，但指针保持悬挂，而不是当对象被销毁时自动设置为nil。

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

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

produced by this snippet of code:

ASIHTTPRequest *request = [[ASIHTTPRequest alloc] initWithURL:...

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

Warning is linked to the use of the object request inside the block.

解决方案

Replying to myself:

My understanding of the documentation says that using keyword block and setting the variable to nil after using it inside the block should be ok, but it still shows the warning.

__block ASIHTTPRequest *request = [[ASIHTTPRequest alloc] initWithURL:...

[request setCompletionBlock:^{
    NSDictionary *jsonDictionary = [[CJSONDeserializer deserializer] deserialize:request.responseData error:nil];
    request = nil;
// ....

    }];

Update: got it to work with the keyword '_weak' instead of '_block', and using a temporary variable:

ASIHTTPRequest *_request = [[ASIHTTPRequest alloc] initWithURL:...
__weak ASIHTTPRequest *request = _request;

[request setCompletionBlock:^{
    NSDictionary *jsonDictionary = [[CJSONDeserializer deserializer] deserialize:request.responseData error:nil];
    // ...
    }];

If you want to also target iOS 4, use __unsafe_unretained instead of __weak. Same behavior, but the pointer stays dangling instead of being automatically set to nil when the object is destroyed.

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