iPhone7、7P iOS10.2及以下系统转场动画出现白屏bug的解决办法

- (UIView *)imageFromView:(UIView *)snapView{
        UIGraphicsBeginImageContext(snapView.frame.size);
        CGContextRef context = UIGraphicsGetCurrentContext();
        [snapView.layer renderInContext:context];
        UIImage * targetImage = UIGraphicsGetImageFromCurrentImageContext();
        UIGraphicsEndImageContext();
        UIImageView * tmpView = [[UIImageView alloc] initWithImage:targetImage];
        snapView.frame = snapView.frame;
        return tmpView;
}