obj-c弱自我在一个块中:为什么第二个在两个相似的情况下不需要弱自我 [英] obj-c weak self in a block: why the 2nd one doesn't need a weak self inside in two similar cases

问题描述

我终于发现我的内存错误是由在一个块中强烈引用self引起的.但是我不知道为什么在类似情况下不需要弱点:

I finally found my memory bug is caused by referring self strongly in a block. But I don't know why in a similar case, the weak is not needed:

我有一个CameraCaptureManager类来执行图像捕获任务，而CameraViewController具有此管理器的强大属性.管理器的弱委托属性指向控制器.

I have a CameraCaptureManager class doing image capture tasks, and a CameraViewController has a strong property of this manager. The manager has weak delegate property pointing back to the controller.

这是我必须在管理器中使用weakSelf的地方，否则-(void)dealloc将不会被调用:

This is where I must use weakSelf in the manager, otherwise -(void)dealloc won't be called:

    // in CameraCaptureManager
    __weak CameraCaptureManager *weakSelf = self;
    void (^deviceOrientationDidChangeBlock)(NSNotification *) = ^(NSNotification *notification) {
        UIDeviceOrientation deviceOrientation = [[UIDevice currentDevice] orientation];
        [weakSelf updateVideoOrientation:deviceOrientation];
    };
    self.deviceOrientationDidChangeObserver = [notificationCenter addObserverForName:UIDeviceOrientationDidChangeNotification
                                                                              object:nil
                                                                               queue:nil
                                                                          usingBlock:deviceOrientationDidChangeBlock];  

管理器强烈握持deviceOrientationDidChangeObserver，因此需要weakSelf来打破内存保留周期.很好，我明白了...但是我发现我没有在同一个类的类似情况下使用weakSelf:

The manager holds the deviceOrientationDidChangeObserver strongly, so weakSelf is needed to break the memory retain cycle. That's fine, I got that... but I find I don't have use weakSelf in a similar case in the same class:

[self.stillImageOutput captureStillImageAsynchronouslyFromConnection:captureConnection
                                                   completionHandler:^(CMSampleBufferRef imageDataSampleBuffer, NSError *error){

                                                       UIImage *image = nil;

                                                       if (imageDataSampleBuffer != NULL) {
                                                           NSData *imageData = [AVCaptureStillImageOutput jpegStillImageNSDataRepresentation:imageDataSampleBuffer]; 
                                                           image = [[UIImage alloc] initWithData:imageData];
                                                       } 

                                                       if ([self.delegate respondsToSelector:@selector(captureManager:capturedStillImage:)]) {
                                                           [self.delegate captureManager:weakSelf capturedStillImage:image];
                                                       }
                                                   }]; 

管理器还强烈持有stillImageOutput，但是为什么我可以在完成块中使用强大的"self"?管理器对象在此块内部具有强大的self来进行dealloc.我很困惑，请说明一下.

The manager also holds the stillImageOutput strongly, but why I can use the strong "self" in the completion block? The manager object gets dealloc with this strong self inside the block. I'm confused, please shed some light.

即使在第二种情况下也不会导致任何保留周期，我还需要使用weakSelf吗?

Also do I need to use weakSelf in the 2nd case even when it won't cause any retain cycle?

推荐答案

在第二个代码示例中，您有一个 temporary 保留周期.调用completionHandler块后，将释放该块并与捕获的self一起释放，因此 释放周期中断了.

In your second code example you have a temporary retain cycle. When the completionHandler block has been called, the block is released and with it the captured self, so that the release cycle is broken.

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