iphone - 正确使用 transitionFromViewController :toViewController:duration:options:animations:completion:

Question

我似乎找不到关于如何正确使用 transitionFromViewController:toViewController:duration:options:animations:completion: 的好例子。

这是正确的吗？ (假设我想用另一个 VC 交换)

// Assume fromVC and toVC view controllers are defined and fromVC is already added as a child view controller
[self addChildViewController:toVC];

[self transitionFromViewController:fromVC toViewController:toVC duration:0.3 options:UIViewAnimationOptionTransitionCrossDissolve animations:NULL completion:^(BOOL finished) {
    [fromVC willMoveToParentViewController:nil];
    [fromVC removeFromParentViewController];
    [toVC didMoveToParentViewController:self];
}];

文档并不清楚何时调用什么:

The addChildViewController: method calls the willMoveToParentViewController: method of the view controller to be added as a child before adding it, but it does not call the didMoveToParentViewController: method. The container view controller class must call the didMoveToParentViewController: of the child view controller after the transition to the new child is complete or, if there is no transition, immediately after calling the addChildViewController: method.

Likewise, it is is the responsibility of the container view controller to call the willMoveToParentViewController: method before calling the removeFromParentViewController: method. The removeFromParentViewController: method calls the didMoveToParentViewController: method of the child view controller.

另一件事是，在这种情况下如何使用动画 block ？请注意，在上面的代码中，我只是放置了 NULL。 (我对 block 本身很熟悉，我只是不确定在这个里面放什么)

Answer 1

我过去也做过类似的事情。但是，我会将 -willMoveToParentViewController: 移到完成 block 之外，因为该 View Controller 应该在移动之前得到通知(即，在完成 block 运行时，fromVC已经将其父 VC 设置为 nil。所以总而言之，是这样的:

[self addChildViewController:toVC];
[fromVC willMoveToParentViewController:nil];

[self transitionFromViewController:fromVC toViewController:toVC duration:0.3 options:UIViewAnimationOptionTransitionCrossDissolve animations:^{} completion:^(BOOL finished) {
    [fromVC removeFromParentViewController];
    [toVC didMoveToParentViewController:self];
}];

根据方法文档，就动画而言，永远不要将此参数设置为 NULL。如果您没有要设置动画的 View 属性，则只需向它传递一个空 block ^{}。基本上，此参数用于在过渡期间为 View 层次结构中的 View 属性设置动画。动画属性列表可以在 the UIView documentation 中找到。在“动画”标题下。例如，假设您不希望由 fromVC 处理的整个 View 交叉融合，而只希望其 View 层次结构中名为 subview1 的一个 subview 淡出。您可以使用动画 block 执行此操作:

[self addChildViewController:toVC];
[fromVC willMoveToParentViewController:nil];

[self transitionFromViewController:fromVC 
                  toViewController:toVC
                          duration:0.3
                           options:UIViewAnimationOptionTransitionNone
                        animations:^{
                                       [subview1 setAlpha:0.0];
                                   }
                        completion:^(BOOL finished) {
                                       [fromVC removeFromParentViewController];
                                       [toVC didMoveToParentViewController:self];
                                   }];