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我正在使用UIViewControllerTransitioningDelegate在两个视图控制器（从 a MKMapView）到基于 ( AVFoundation) 构建的自定义相机之间构建自定义转换。一切都很顺利，直到我打电话presentViewController，电话似乎挂了大约 1 秒钟（当我注销所有内容时）。当我转换到一个更简单的视图时，这甚至似乎发生了（我有一个只显示 a 的视图控制器，UITextview即使在实际调用转换之前似乎有大约 0.4 - 0.5 秒的延迟）。

这就是我目前所说的过渡

 dispatch_async(dispatch_get_main_queue(), ^{
        UIStoryboard*  sb = [UIStoryboard storyboardWithName:@"Main" bundle:nil];
        CameraViewController *cvc2 = [sb instantiateViewControllerWithIdentifier:@"Camera"];

        cvc2.modalPresentationStyle = UIModalPresentationFullScreen; // Needed for custom animations to work
        cvc2.transitioningDelegate = self; //Conforms to the UIViewControllerTransitioningDelegate protocol
        [self presentViewController:cvc2 animated:YES completion:nil];
    });

这是我animateTransition的调用方法。非常直截了当，目前呈现这个的视图只有一个MkMapView（没有额外的视图或方法）。

-(void)animateTransition:(id<UIViewControllerContextTransitioning>)transitionContext {

if (self.type == MapAnimationTypePresent) {//From map to another view

    UIView *containerView = [transitionContext containerView];
    UIViewController *fromViewController = [transitionContext viewControllerForKey:UITransitionContextFromViewControllerKey];
    UIViewController *toViewController = [transitionContext viewControllerForKey:UITransitionContextToViewControllerKey];

// Amazing category for iOS 7 compatibility found here - http://stackoverflow.com/a/25193675/2939977 
    UIView *toView = [toViewController viewForTransitionContext:transitionContext];
    UIView *fromView = [fromViewController viewForTransitionContext:transitionContext];

    toView.frame = self.view.frame;
    fromView.frame = self.view.frame;

    //Add 'to' view to the hierarchy
    toView.alpha = 0;
    [containerView insertSubview:toView aboveSubview:fromView];

    [UIView animateWithDuration:.5 animations:^{

        toView.alpha = 1;

    }completion:^(BOOL finished) {
        [transitionContext completeTransition:YES];
    }];
}

任何帮助是极大的赞赏。

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