Question

我正在尝试捕获UWP上TabbedPage的一次重新捕获事件。

在this page中，我看到您需要创建一个自定义渲染器。当我尝试使用Xamarin.Forms.Platform.UWP.TabbedPageRenderer时，找不到任何合适的事件要订阅。

我尝试了Tapped和Focused事件，但是它们似乎没有达到我的预期。

您如何检测是否在UWP上重新点击了一个标签？

这是我到目前为止尝试过的：

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

简短的回答是，据我所知，至少在不深入研究Xamarin的情况下，您无法轻易检测到UWP上的选项卡重新点击/重新选择.Forms源代码有点了解它们如何实现uWP TabbedPageRenderer。

这是我的实现方式：

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。鉴于尚未记录，因此从理论上可以在将来版本的Xamarin.Forms上进行更改，这并不是理想的选择，但是它已经稳定了一段时间。

这足以为您解决问题，但请在此处查看更多详细信息：https://criticalhittech.com/2017/09/25/tab-reselection-in-xamarin-forms-part-2/。

Answer 2

根据DavidS的回答，这是我使用的代码，该代码还处理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，我已经更新了您的代码，希望对您有所帮助：

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;
    }
}

在TabbedPage上单击事件

3 个答案: