阻止將自身作爲引發編譯器警告的方法的參數

Question

我試圖創建一個回調，在發生故障延遲後重試該方法。我正在發出此警告：

「在此塊中強烈捕獲故障塊可能會導致保留週期。」

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; 

問題：如何使這項工作正常進行？

（我一直在讀通過其他SO問題 - 還沒有找到一個匹配的是，雖然不會感到驚訝，如果一個人在那裏）

Answer 1

添加__unsafe_unretained工作，如：

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

雖然看起來可能__weak可以工作，在實踐中引起了我的應用程序崩潰。 this answer解釋原因並不是100％清楚，但我想象的是這些。

Answer 2

是，該塊需要捕獲本身（以及self）作爲弱參考。

如果您使用ARC *，它應該是這樣的：

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，更換__block __weak和__weak以上只是__block。

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_{*：Objective-C中自動引用計數}