使用ARC在自己的完成块中引用NSOperation对象 [英] Referencing an NSOperation object in its own completion block with ARC

问题描述

我很难将一些NSOperation代码转换为ARC.我的操作对象使用了一个完成块，该完成块又包含一个GCD块，用于更新主线程上的UI.因为我从自己的完成对象内部引用了操作对象，所以我使用__weak指针来避免内存泄漏.但是，在我的代码运行时，指针已设置为nil.

I'm having difficulty converting some NSOperation code to ARC. My operation object uses a completion block, which in turn contains a GCD block that updates the UI on the main thread. Because I reference my operation object from inside its own completion block, I'm using a __weak pointer to avoid a memory leak. However, the pointer is already set to nil by the time my code runs.

我将其范围缩小到此代码示例.有人知道我哪里出了问题，以及实现此目标的正确方法吗?

I've narrowed it down to this code sample. Anyone know where I went wrong, and the right way to accomplish this?

NSOperationSubclass *operation = [[NSOperationSubclass alloc] init];
__weak NSOperationSubclass *weakOperation = operation;

[operation setCompletionBlock:^{
    dispatch_async( dispatch_get_main_queue(), ^{

        // fails the check
        NSAssert( weakOperation != nil, @"pointer is nil" );

        ...
    });
}];

推荐答案

对此我不确定，但是正确的方法可能是在有问题的变量中添加__block，然后将其设置为nil块的末尾以确保将其释放. 请参阅此问题.

I'm not certain about this, but the correct way to do it is possibly to add __block to the variable in question, and then set it to nil at the end of the block to ensure that it is released. See this question.

您的新代码如下:

NSOperationSubclass *operation = [[NSOperationSubclass alloc] init];
__block NSOperationSubclass *weakOperation = operation;

[operation setCompletionBlock:^{
    dispatch_async( dispatch_get_main_queue(), ^{

        // fails the check
        NSAssert( weakOperation != nil, @"pointer is nil" );

        ...
        weakOperation = nil;
    });

}];

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