阻止将自身作为引发编译器警告的方法的参数

Question

我试图创建一个回调，在发生故障延迟后重试该方法。我正在发出此警告：

“在此块中强烈捕获故障块可能会导致保留周期。”

typedef void (^MyCallbackBlock)(NSObject *); 

... 

__block MyObject *blockSelf = self; 
__block MyCallbackBlock successBlock = ^(NSObject *someObject) 
{ 
    // To be completed 
}; 
__block MyCallbackBlock failureBlock = ^(NSObject *someObject) 
{ 
    double delayInSeconds = 2.0; 
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC)); 
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){ 
     [blockSelf doSomething:someObject onSuccess:successBlock onFailure:failureBlock]; // <-- Warning is here 
    }); 
}; 
[blockSelf doSomething:someObject onSuccess:successBlock onFailure:failureBlock]; 

... 

- (void)doSomething:(NSObject *)someObject 
      onSuccess:(MyCallbackBlock)successBlock 
      onFailure:(MyCallbackBlock)failureBlock; 

问题：如何使这项工作正常进行？

（我一直在读通过其他SO问题 - 还没有找到一个匹配的是，虽然不会感到惊讶，如果一个人在那里）

Answer 1

添加__unsafe_unretained工作，如：

__unsafe_unretained __block MyCallbackBlock successBlock = ^(NSObject *someObject) 
{ 
    // To be completed 
}; 

虽然看起来可能__weak可以工作，在实践中引起了我的应用程序崩溃。 this answer解释原因并不是100％清楚，但我想象的是这些。

Answer 2

是，该块需要捕获本身（以及self）作为弱参考。

如果您使用ARC *，它应该是这样的：

MyObject *__weak blockSelf = self; 
__block __weak MyCallbackBlock weakSuccessBlock; 
MyCallbackBlock successBlock = weakSuccessBlock = ^(NSObject *someObject) 
{ 
    // To be completed 
}; 
__block __weak MyCallbackBlock weakFailureBlock; 
MyCallbackBlock failureBlock = weakFailureBlock = ^(NSObject *someObject) 
{ 
    MyCallbackBlock strongSuccessBlock = weakSuccessBlock; 
    MyCallbackBlock strongFailureBlock = weakFailureBlock; 
    double delayInSeconds = 2.0; 
    dispatch_time_t popTime = dispatch_time(DISPATCH_TIME_NOW, (int64_t)(delayInSeconds * NSEC_PER_SEC)); 
    dispatch_after(popTime, dispatch_get_main_queue(), ^(void){ 
     [blockSelf doSomething:someObject onSuccess:strongSuccessBlock onFailure:strongFailureBlock]; 
    }); 
}; 

如果你不使用ARC，更换__block __weak和__weak以上只是__block。

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_{*：Objective-C中自动引用计数}