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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:

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.

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];

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];
                                                       }
                                                   }];

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.

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

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1 回答 1

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在您的第二个代码示例中，您有一个临时保留周期。当completionHandler块被调用时，块被释放并随之被捕获self，这样释放周期就被打破了。

于 2013-07-28T17:51:18.560 回答