最近在使用系统拍照，只要一点击拍照就崩溃，不稳定复现，最终抓到Log如下:[UIKeyboardTaskQueue waitUntilAllTasksAreFinished] may only be called from the main thread.
最终定位到代码:

    [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
        if (granted) {
            [self presentViewController:self.imagePickerController animated:YES completion:^{}];
        }
    }];

在回调里面进行present操作，Block块中present不是在主线程执行，会报错，需要在主线程进行present操作:

    [AVCaptureDevice requestAccessForMediaType:AVMediaTypeVideo completionHandler:^(BOOL granted) {
        if (granted) {
            dispatch_async(dispatch_get_main_queue(), ^{
                    [self presentViewController:self.imagePickerController animated:YES completion:^{}]
            });
        }
    }];

简书-FlyElephant 参考资料