缓慢的presentViewController性能

Question

我UIViewControllerTransitioningDelegate用来在两个视图控制器(从a MKMapView)到构建在(AVFoundation)上的自定义Camera 之间构建自定义转换.一切顺利,直到我打电话presentViewController,手机似乎挂了大约1秒钟(当我记录所有东西时).这甚至似乎发生在我转换到更简单的视图时(我有一个视图控制器只显示一个UITextview,甚至在实际调用转换之前似乎有大约.4 - .5秒的延迟).

这是我现在称之为过渡的方式

 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打电话的方法.非常直接,目前呈现此视图的视图上只有一个MkMapView(没有其他视图或方法).

-(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];
    }];
}

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