参考块中的self计数 [英] Reference Counting of self in Blocks

问题描述

我正试图了解对象生存期和引用计数如何与代码块交互。在下面的代码中，我只是做一个简单的动画，当UINavigationController的堆栈顶视图被交换时闪烁。棘手的部分是弹出的视图控制器是定义此代码的视图。

I'm trying to get my head around how object lifetime and reference counting interact with code blocks. In the following code I'm just doing a simple animation that flashes as the top view on a UINavigationController's stack is swapped. The tricky part is that the popped view controller is the one where this code is defined.

[UIView animateWithDuration:0.2 
        animations:^{self.navigationController.view.alpha = 0.0;}
        completion:^(BOOL finished){ 
                UINavigationController *navController = self.navigationController;  

                [self.navigationController popViewControllerAnimated:NO]; 
                [navController pushViewController:nextView animated:NO];
                [nextView release];

                [UIView animateWithDuration:0.2 
                        animations:^{navController.view.alpha = 1.0;}];                    
                 }];    

我的问题是（忽略动画的样子），这是正确的方法吗？内存管理的角度。特别是：

My question is (ignoring what the animation looks like), is this the correct way to do this from a memory management perspective. In particular:

（1）当使用这种方法进行pop + push循环时，是否正确不再需要保留self，如其他类似的例子不使用块？

(1) When using this approach for the pop+push cycle, is it correct that it is no longer necessary to retain self, as in other similar examples that do not use blocks?

（2）使用这些块调用animateWithDuration：...是否保留定义视图控制器（self），直到块执行？

(2) Does invoking animateWithDuration:... with the these blocks retain the defining view controller (self) until the blocks execute?

推荐答案

（1）当使用这种方法时，pop + push循环，是否正确不再需要保留self，就像其他不使用块的类似示例一样？

(1) When using this approach the the pop+push cycle, is it correct that it is no longer necessary to retain self, as in other similar examples that do not use blocks?

这是正确的。如果nextView是局部变量，这些块会自动保留self，navController和nextView。

It is correct. These blocks automatically retain self, navController and nextView if nextView is local variable.

（2）调用animateWithDuration：...块保留定义视图控制器（self），直到块执行？

(2) Does invoking animateWithDuration:... with the these blocks retain the defining view controller (self) until the blocks execute?

这些块通过此方法从堆栈复制到堆中。这些块在执行后被释放。然后self，navController和nextView从这些块中释放。

These blocks are copied to heap from stack by this method. And these blocks are released after execution. And then self, navController and nextView are released from these blocks.

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