iOS 7.1 UIImagePickController 打开相机 Snapshotting a view

在IOS 7.1中使用imagepickcontroller 打开相机的时候执行

    self.picker.delegate = self;
    self.picker.sourceType = UIImagePickerControllerSourceTypeCamera;
    self.picker.showsCameraControls = YES;
    self.picker.modalPresentationStyle = UIModalPresentationOverCurrentContext;
    self.picker.cameraViewTransform = CGAffineTransformMakeScale(1, 1);
    [Controller presentViewController:_picker animated:YES completion:nil];
    
  presentViewController命令中在输出这段命令是怎么回事，看的烦死了。网上的办法试过了，延迟执行。没用啊  
    

Snapshotting a view that has not been rendered results in an empty snapshot. Ensure your view has been rendered at least once before snapshotting or snapshot after screen updates.