cocoa-touch - 为什么 animateWithDuration 动画和完成 block 之间的暂停？

Question

按照 Apple 的建议，我通过对 -animationWithDuration:animation: 进行后续调用来链接 UIView 动画。在 completion:阻止另一个调用 aanimateWithDuration:animation:completion: ，像这样:

[UIView animateWithDuration:scaleDuration delay:0 options:UIViewAnimationOptionCurveEaseIn animations:^{
    // Scale the controllers' views down.
    self.view.transform = CGAffineTransformScale(self.view.transform, 0.8, 0.8);
} completion:^(BOOL finished) {
    // Transition to the new view and push on the new view controller.
    [UIView transitionWithView:self.view duration:1 options:UIViewAnimationOptionCurveLinear | UIViewAnimationOptionTransitionFlipFromLeft animations:^{
        [self pushViewController:viewController animated:NO];
    } completion:^(BOOL finished) {
        [UIView animateWithDuration:scaleDuration delay:0 options:UIViewAnimationOptionCurveLinear animations:
^{
            // Scale back to the original size.
            self.view.transform = CGAffineTransformScale(self.view.transform, 1.25, 1.25);
        } completion:nil];
    }];
}];

动画都按正确的顺序执行，但它们之间有一点延迟，尤其是在 -transitionWithView:duration:options:animations:completion: 之前。称呼。如何平滑动画步骤之间的过渡？

Answer 1

在旁边:
您以这种方式滥用导航 Controller 有什么特别的原因吗？你不能只用presentViewController:animated:completion:将其过渡样式设置为 UIModalTransitionStyleFlipHorizontal ?

回到你的问题:

我很确定口吃来自 pushViewController:animated: 这个简单的事实。隐式必须加载要推送的 View Controller 的 View ，这需要一些时间。

所以如果你不能使用 presentViewController:animated:completion: (或 presentModalViewController:animated: 如果你必须支持 iOS 4)方法，我鼓励你试试这个:

// ensure the view is already loaded when you invoke `pushViewController:animated:`
[viewController view];

// there is no strict need to calculate those in situ, so we do it up front
CGAffineTransform originalTransform = self.view.transform;
CGAffineTransform downscalingTransform = CGAffineTransformScale(originalTransform, 0.8, 0.8);

// I found it hard to read the block-in-a-block-in-a... while editing here, so I've taken them apart:
void (^scaleDownAnimation)() = ^{
    self.view.transform = downscalingTransform;
};

void (^restoreScaleAnimation)() = ^{
    self.view.transform = originalTransform;
};

void (^pushControllerAnimation)() = ^{
    [self pushViewController:viewController animated:NO];
};

void (^pushAnimationCompletion)(BOOL) = ^(BOOL unused) {
    [UIView animateWithDuration:scaleDuration
                          delay:0
                        options:UIViewAnimationOptionCurveLinear
                     animations:restoreScaleAnimation
                     completion:nil];
};

void (^downscaleCompletion)(BOOL) = ^(BOOL unused){
    UIViewAnimationOptions linearFlipFromLeft = UIViewAnimationOptionCurveLinear | UIViewAnimationOptionTransitionFlipFromLeft;
    [UIView transitionWithView:self.view
                      duration:1
                       options:linearFlipFromLeft
                    animations:pushControllerAnimation
                    completion:pushAnimationCompletion];
};

[UIView animateWithDuration:scaleDuration
                      delay:0
                    options:UIViewAnimationOptionCurveEaseIn
                 animations:scaleDown
                 completion:downscaleCompletion];

备注 牛肉在前六行之内，其余的只是为了完整性。