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我将 MvvmCross 用于我的应用程序并从 iPhone 开始。为了实现使用 RequestNavigate 和 Close 在视图之间导航的复杂性，我从 MvxBaseTouchViewPresenter 派生了一个新的演示者。到目前为止，一切都很好。

我现在遇到的问题是可以关闭或显示视图，而之前可见的视图仍在转换中，无论是打开还是关闭。我能想到的解决这个问题的唯一方法是使用视图控制器的 ViewDidAppear 和 ViewDidDisappear 事件处理程序来调用执行下一个视图显示的操作，从而将显示推迟到前一个视图完成其转换之后。

这意味着我必须添加：

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

        DoPostTransitionAction();
    }

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

        DoPostTransitionAction();
    }

    private void DoPostTransitionAction()
    {
        if( _postTransitionAction != null)_postTransitionAction();
    }

    private Action _postTransitionAction;

    public void ShowActionAfterTransition( Action postTransitionAction)
    {
        if( this.IsBeingDismissed || this.IsBeingPresented)
        {
            _postTransitionAction = postTransitionAction;
        }
        else
        {
            _postTransitionAction = null;
            postTransitionAction();
        }
    }

查看控制器，引入一个 IEventViewController 接口，让我添加代码并将演示者的 Show 方法更改为：

    public override void Show(MvxShowViewModelRequest request)
    {
        // find the current top view as it will disappear as a result of
        // showing the requested view
        // note: this will be null for the first show request
        var topViewController = TopViewController;

        // if the request is to roll back an existing stack of views
        // then rollback to the bottom of the stack
        if (request.ClearTop && topViewController != null)
        {
            RollBackStack(topViewController);
        }

        // the top view is about to be 'covered' by the view requested
        // if the top view is transitioning (appearing or disappearing)
        // then wait for it to finish before showing the view requested
        var disappearingViewController = topViewController as IEventViewController;

        // if the top view is disappearing and it's of the 'event' type
        // delay calling Show until after the view has disappeared
        if( disappearingViewController != null)
        {
            // the top view has been requested to close and will fire the
            // 'transition complete' event when it has

            // register the action to perform when the top view has disappeared
            disappearingViewController.ShowActionAfterTransition (() =>
            {
                Show (CreateView(request), true);
            });
        }
        else
        {
            // show the view now as the top view is either not closing
            // or, if it is, is not going to say when it does

            // create a view controller of the type requested
            Show(CreateView(request), true);
        }
    }

我真正想要的是基类中的那些事件处理程序。我想知道如果我不让自己偏离主要发展道路，有什么机会？偏班可以吗？

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