TabbedPage上的Retap事件

Question

我正试图在UWP上捕捉TabbedPage的重拍事件。

从this page，我可以看到你需要创建一个自定义渲染器。当我尝试使用Xamarin.Forms.Platform.UWP.TabbedPageRenderer时，我找不到任何适当的事件来订阅。

我已经尝试了Tapped和Focused事件，但它们似乎没有像我期望的那样工作。

如何检测UWP上是否重新点击了标签？

这是我到目前为止所尝试的：

public class TabbedPageCustomRenderer : TabbedPageRenderer
{
    private TabbedHomePage _page;
    protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);

        if (e.NewElement != null)
        {
            _page = (TabbedHomePage)e.NewElement;
        }
        else
        {
            _page = (TabbedHomePage)e.OldElement;
        }

        //_page.Focused += _page_Focused;
        //this.Control.Tapped += Control_Tapped;

        // what should I subscribe to?
    }

    private async void _page_Focused(object sender, Xamarin.Forms.FocusEventArgs e)
    {
        if (_page?.CurrentPage?.Navigation != null && _page.CurrentPage.Navigation.NavigationStack.Count > 0)
        {
            await _page.CurrentPage.Navigation.PopToRootAsync();
        }
    }

    private async void Control_Tapped(object sender, Windows.UI.Xaml.Input.TappedRoutedEventArgs e)
    {
        if (_page?.CurrentPage?.Navigation != null && _page.CurrentPage.Navigation.NavigationStack.Count > 0)
        {
            await _page.CurrentPage.Navigation.PopToRootAsync();
        }
    }
}

Answer 1

简单的回答是，据我所知，你不能轻易地检测UWP上的标签重新选择/重选，至少没有深入研究Xamarin.Forms源代码，看看他们是如何实现uWP TabbedPageRenderer的。

以下是我实现它的方法：

public class MainTabPageRenderer : TabbedPageRenderer
{
    private Xamarin.Forms.Page _prevPage;

    protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);

        Control.Tapped += Control_Tapped;
        _prevPage = Control.SelectedItem as Xamarin.Forms.Page;
    }

    private async void Control_Tapped(object sender, Windows.UI.Xaml.Input.TappedRoutedEventArgs e)
    {
        var src = e.OriginalSource as TextBlock;
        if (src != null
             && src.Name == "TabbedPageHeaderTextBlock"
             && Element is TabReselectDemo.MainPage)
        {
            var newPage = src.DataContext as Xamarin.Forms.Page;
            if (newPage == _prevPage)
            {
                // do your thing here, a tab retap happened, like:
                await newPage.Navigation.PopToRootAsync();
            }
            _prevPage = newPage;
        }
    }
}

TabbedPageHeaderTextBlock是UWP渲染器内部的一部分。鉴于它没有记录，这并不理想，因为它理论上可以改变未来版本的Xamarin.Forms，但它已经稳定了一段时间。

这应该足以为你解决，但更多细节在这里：https://criticalhittech.com/2017/09/25/tab-reselection-in-xamarin-forms-part-2/。

Answer 2

基于DavidS的答案，这里是我使用的代码，它也处理UWP选项卡中的图标：

// this is C# 7, so will only work with a recent c# compiler
public class TabbedPageCustomRenderer : TabbedPageRenderer
{
    private Xamarin.Forms.Page _prevPage;

    protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);

        Control.Tapped += Control_Tapped;
        _prevPage = Control.SelectedItem as Xamarin.Forms.Page;
    }

    private async void Control_Tapped(object sender, Windows.UI.Xaml.Input.TappedRoutedEventArgs e)
    {
        // replace 'TabbedHomePage' with whatever your page type is with the tabs
        if (!(this.Element is TabbedHomePage))
            return;

        switch (e.OriginalSource)
        {
            case Image image when image.Parent is StackPanel:
                {
                    var sp = (StackPanel)image.Parent;

                    var tb = sp.Children.Where(c => c is TextBlock).FirstOrDefault() as TextBlock;

                    await HandleRetab(tb);
                    break;
                }
            case TextBlock tb:
                {
                    await HandleRetab(tb);
                    break;
                }
            default:
                break;
        }

        async Task HandleRetab(TextBlock tb)
        {
            if (tb == null)
                return;

            var newPage = tb.DataContext as Xamarin.Forms.Page;
            if (newPage == _prevPage &&
                tb.Name == "TabbedPageHeaderTextBlock")
            {
                // do your thing here, a tab retap happened, like:
                await newPage.Navigation.PopToRootAsync();
            }

            _prevPage = newPage;
        }
    }
}

Answer 3

根据您的解释，我已更新您的代码，希望这将有所帮助：

public class TabbedPageCustomRenderer : TabbedPageRenderer
{
    private TabbedHomePage _page;
    bool isRetap = false;
    protected override void OnElementChanged(VisualElementChangedEventArgs e)
    {
        base.OnElementChanged(e);

        if (e.NewElement != null)
        {
            _page = (TabbedHomePage)e.NewElement;
        }
        else
        {
            _page = (TabbedHomePage)e.OldElement;
        }

        //_page.Focused += _page_Focused;
        this.Control.Tapped += Control_Tapped;

        // what should I subscribe to?
    }

    private async void _page_Focused(object sender, Xamarin.Forms.FocusEventArgs e)
    {
        if (_page?.CurrentPage?.Navigation != null && _page.CurrentPage.Navigation.NavigationStack.Count > 0)
        {
            await _page.CurrentPage.Navigation.PopToRootAsync();
        }
    }

    private async void Control_Tapped(object sender, Windows.UI.Xaml.Input.TappedRoutedEventArgs e)
    {
        if (isRetap && _page?.CurrentPage?.Navigation != null && _page.CurrentPage.Navigation.NavigationStack.Count > 0)
        {
            await _page.CurrentPage.Navigation.PopToRootAsync();
        }
        isRetap = true;
    }
}