ios - 为什么我们需要在成功解雇转换后从容器 View 中删除 toView？

Question

我正在阅读 View Controller Programming Guide for iOS这些天，它说:

Because transitions can be canceled, you should use the return value of the transitionWasCancelled method of the context object to determine what cleanup is required. When a presentation is canceled, your animator must undo any modifications it made to the view hierarchy. A successful dismissal requires similar actions.

在 Presentations and Transitions->Customizing the Transition Animations->Implementing Your Animator Objects->Cleaning Up After the Animations.

以及Apple提供的示例代码:

BOOL success = ![transitionContext transitionWasCancelled];

// After a failed presentation or successful dismissal, remove the view.
if ((self.presenting && !success) || (!self.presenting && success)) {
     [toView removeFromSuperview];
}

// Notify UIKit that the transition has finished
[transitionContext completeTransition:success];

我知道dismissal首先要给容器view添加toView，为什么dismissal成功后还要remove toView呢？我已经测试过，如果我在成功解雇后不调用 removeFromSuperview，一切正常。

如果解雇失败会怎样？它仍然会显示呈现的 View Controller 还是关闭它并显示呈现的 View Controller ？

有人知道吗？非常感谢。

Answer 1

通常，当您在交互中使用自定义动画时，就会发生这种情况。但是，如果万一动画被取消并且您不处理取消状态，那么它将保持呈现的 View Controller 状态。(在您的情况下)