UIScrollView _getDelegateZoomView bug 经历

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[UIScrollView _getDelegateZoomView]
UIKit -[UIScrollView_offsetForCenterOfPossibleZoomView:withIncomingBoundsSize:] + 64

bugly 腾讯给出的解释

闪退场景一：recorder deleteRecording 以前 先判断文件是否存在，不然会形成过分释放，解决方法:

if ([[NSFileManager defaultManager] fileExistsAtPath:self.recorder.url.path]) {
if ([self.recorder deleteRecording])
NSLog(@"Failed to delete %@", self.recorder.url);
}

闪退场景二： delegate = nil 。
将XXViewContrller设置为delegate时，当页面发生跳转时，XXViewController的对象会被释放，这是代码走到[_delegate callbackMethod],便出现crash。解决方法有二：1.将@property (nonatomic ,assign) id delegate; 中 assign关键字改成weak。 2.在XXViewController的delloc方法中添加：xxx.delegate = nil;

http://www.cnblogs.com/smileEvday/p/iOSCrash.html

• http://artsy.github.io/blog/2015/07/30/Notorious-BUG-Part-1/

Perfect, an exact replica of the crash report, so now I know with confidence that the problem is that theARArtworkViewControlleris released by the time that method is called.

问题的方向是对的，都是vc提早释放，而后野指针的问题引发，
block 强引用一样会产生此类问题