自定义容器控制器：transitionFromViewController：在动画之前查看未正确布局

Question

这是一个问题和部分解决方案。

---

*示例项目：

https://github.com/JosephLin/TransitionTest

---

问题1：

使用transitionFromViewController:...时，toViewController的{​​{1}}完成的布局在转换动画开始时不会显示。换句话说，在动画期间显示预布局视图，并且它的内容会在动画后捕捉到布局后的位置。

问题2：

如果我自定义导航栏viewWillAppear:的背景，则在动画播放前，条形按钮会显示错误的大小/位置，并在动画结束时捕捉到正确的大小/位置，类似于问题1。

---

为了演示这个问题，我制作了一个裸骨的自定义容器控制器来执行一些自定义视图转换。它几乎是一个UINavigationController副本，它在视图之间进行交叉溶解而不是推送动画。

“推送”方法如下所示：

UIBarButtonItem

现在，- (void)pushController:(UIViewController *)toViewController { UIViewController *fromViewController = [self.childViewControllers lastObject]; [self addChildViewController:toViewController]; toViewController.view.frame = self.view.bounds; NSLog(@"Before transitionFromViewController:"); [self transitionFromViewController:fromViewController toViewController:toViewController duration:0.5 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{} completion:^(BOOL finished) { [toViewController didMoveToParentViewController:self]; }]; } （我正在推动的视图控制器）需要在DetailViewController中布局其内容。它不能在viewWillAppear:中执行，因为它当时没有正确的帧。

出于演示目的，viewDidLoad将其标签设置为DetailViewController，viewDidLoad和viewWillAppear中的不同位置和颜色：

viewDidAppear

---

现在，当推动- (void)viewDidLoad { [super viewDidLoad]; NSLog(@"%s", __PRETTY_FUNCTION__); CGRect rect = self.descriptionLabel.frame; rect.origin.y = 50; self.descriptionLabel.frame = rect; self.descriptionLabel.text = @"viewDidLoad"; self.descriptionLabel.backgroundColor = [UIColor redColor]; } - (void)viewWillAppear:(BOOL)animated { [super viewWillAppear:animated]; NSLog(@"%s", __PRETTY_FUNCTION__); CGRect rect = self.descriptionLabel.frame; rect.origin.y = 200; self.descriptionLabel.frame = rect; self.descriptionLabel.text = @"viewWillAppear"; self.descriptionLabel.backgroundColor = [UIColor yellowColor]; } - (void)viewDidAppear:(BOOL)animated { [super viewDidAppear:animated]; NSLog(@"%s", __PRETTY_FUNCTION__); CGRect rect = self.descriptionLabel.frame; rect.origin.y = 350; self.descriptionLabel.frame = rect; self.descriptionLabel.text = @"viewDidAppear"; self.descriptionLabel.backgroundColor = [UIColor greenColor]; } 时，我希望在动画开头的DetailViewController处看到标签（左图），然后跳转到y =200动画完成（右图）。

动画前后的预期视图。

---

然而，标签位于y = 350，好像在y=50中进行的布局在动画发生之前没有制作（左图）。但请注意标签的背景设置为黄色（viewWillAppear指定的颜色）！

动画开头的布局错误。请注意，条形按钮也以错误的位置/大小开始。

---

控制台日志
TransitionTest [49795：c07] - [DetailViewController viewDidLoad]
TransitionTest [49795：c07]在transitionFromViewController之前：
TransitionTest [49795：c07] - [DetailViewController viewWillAppear：]
TransitionTest [49795：c07] - [DetailViewController viewWillLayoutSubviews]
TransitionTest [49795：c07] - [DetailViewController viewDidLayoutSubviews]
TransitionTest [49795：c07] - [DetailViewController viewDidAppear：]
请注意viewWillAppear被称为 AFTER viewWillAppear:

---

问题1的解决方案

好的，这里是部分解决方案部分。通过明确调用transitionFromViewController:和beginAppearanceTransition:到endAppearanceTransition，视图将在转换动画发生之前具有正确的布局：

toViewController

请注意- (void)pushController:(UIViewController *)toViewController { UIViewController *fromViewController = [self.childViewControllers lastObject]; [self addChildViewController:toViewController]; toViewController.view.frame = self.view.bounds; [toViewController beginAppearanceTransition:YES animated:NO]; NSLog(@"Before transitionFromViewController:"); [self transitionFromViewController:fromViewController toViewController:toViewController duration:0.5 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{} completion:^(BOOL finished) { [toViewController didMoveToParentViewController:self]; [toViewController endAppearanceTransition]; }]; } 现在被称为viewWillAppear: TransitionTest [18398：c07] - [DetailViewController viewDidLoad]
TransitionTest [18398：c07] - [DetailViewController viewWillAppear：]
TransitionTest [18398：c07]在transitionFromViewController之前：
TransitionTest [18398：c07] - [DetailViewController viewWillLayoutSubviews]
TransitionTest [18398：c07] - [DetailViewController viewDidLayoutSubviews]
TransitionTest [18398：c07] - [DetailViewController viewDidAppear：]

---

但这不能解决问题2！

无论出于何种原因，导航按钮在转换动画开始时仍以错误的位置/大小开头。我花了很多时间试图找到正确的解决方案，但没有运气。我开始觉得这是transitionFromViewController:或transitionFromViewController:或其他什么的错误。请非常感谢您对此问题提供的任何见解。谢谢！

---

我尝试过的其他解决方案

• 在UIAppearance
之前致电[self.view addSubview:toViewController.view];

它实际上为用户提供了正确的结果，修复了问题1和2。问题是，transitionFromViewController:和viewWillAppear都会被调用两次！如果我想在viewDidAppear中进行一些广泛的动画或计算，那就有问题了。

• 在viewDidAppear
之前致电[toViewController viewWillAppear:YES];

我认为这与调用transitionFromViewController:几乎相同。它修复了问题1，但没有修复问题2.此外，文档说不要直接调用beginAppearanceTransition:！

• 使用viewWillAppear代替[UIView animateWithDuration:]

像这样：     [self addChildViewController：toViewController];     [self.view addSubview：toViewController.view];     toViewController.view.alpha = 0.0;

transitionFromViewController:

它解决了问题2，但视图以[UIView animateWithDuration:0.5 animations:^{ toViewController.view.alpha = 1.0; } completion:^(BOOL finished) { [toViewController didMoveToParentViewController:self]; }]; 中的布局开始（标签为绿色，y = 350）。此外，交叉溶解不如使用viewDidAppear

那么好

Answer 1

好的，在toViewController.view中添加layoutIfNeeded似乎可以解决问题 - 这会在视图显示在屏幕上之前正确显示视图（没有添加/删除），并且不再有奇怪的双重viewDidAppear：call。

- (void)pushController:(UIViewController *)toViewController
{
    UIViewController *fromViewController = [self.childViewControllers lastObject];

    [self addChildViewController:toViewController];

    toViewController.view.frame = self.view.bounds;
    [toViewController.view layoutIfNeeded];

    NSLog(@"Before transitionFromViewController:");
    [self transitionFromViewController:fromViewController
                      toViewController:toViewController
                              duration:0.5
                               options:UIViewAnimationOptionTransitionCrossDissolve
                            animations:^{}
                            completion:^(BOOL finished) {
                            }];

}

Answer 2

遇到同样的问题，您只需要转发外观事务和UIView.Animate。这种方法解决了所有问题，但没有创建新问题。这是一些C＃代码（xamarin）：

var fromView = fromViewController.View;
var toView = toViewController.View;

fromViewController.WillMoveToParentViewController(null);
AddChildViewController(toViewController);

fromViewController.BeginAppearanceTransition(false, true);
toViewController.BeginAppearanceTransition(true, true);

var frame = fromView.Frame;
frame.X = -viewWidth * direction;
toView.Frame = frame;
View.Add(toView);

UIView.Animate(0.3f,
    animation: () =>
    { 
        toView.Frame = fromView.Frame; 
        fromView.MoveTo(x: viewWidth * direction);
    },
    completion: () =>
    {
        fromView.RemoveFromSuperview();

        fromViewController.EndAppearanceTransition();
        toViewController.EndAppearanceTransition();

        fromViewController.RemoveFromParentViewController();
        toViewController.DidMoveToParentViewController(this);
    }
);

当然你应该禁用外观方法的自动转发并手动完成：

public override bool ShouldAutomaticallyForwardAppearanceMethods
{
    get { return false; }
}

public override void ViewWillAppear(bool animated)
{
    base.ViewWillAppear(animated);
    CurrentViewController.BeginAppearanceTransition(true, animated);
}

public override void ViewDidAppear(bool animated)
{
    base.ViewDidAppear(animated);
    CurrentViewController.EndAppearanceTransition();
}

public override void ViewWillDisappear(bool animated)
{
    base.ViewWillDisappear(animated);
    CurrentViewController.BeginAppearanceTransition(false, animated);
}

public override void ViewDidDisappear(bool animated)
{
    base.ViewDidDisappear(animated);
    CurrentViewController.EndAppearanceTransition();
}