c# - 隐藏在 Xamarin Forms Android 中时如何禁用单击 TabbedPage 菜单项？

Question

我有一个 XF 应用程序，它在用户处于测验模式时隐藏 TabbedPage 菜单，并在用户停止测验模式时再次显示它。下面是我如何隐藏和显示菜单的代码:

public static void ClearNav()
{
   navHomeTabPage.Icon = "";
   navHomeTabPage.Title = "";
   // more items
}

public static void SetNav()
{
   navHomeTabPage.Icon = "home.png";
   navHomeTabPage.Title = "Home";
   // more items
}

有了这个，我可以隐藏菜单项，但它们仍然可以点击。有没有办法在 Xamarin.Android 中禁用此点击事件？我找不到关于此的任何文章/帖子。感谢您的帮助。

编辑:

我正在使用 BottomNavigationView 将我的选项卡菜单放在底部。

public class BottomTabPageRenderer : TabbedPageRenderer, BottomNavigationView.IOnNavigationItemSelectedListener, BottomNavigationView.IOnNavigationItemReselectedListener
{
   private MainPage _page;
   protected override void OnElementChanged(ElementChangedEventArgs<TabbedPage> e)
   {
      base.OnElementChanged(e);

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

      // More codes
   }

   bool BottomNavigationView.IOnNavigationItemSelectedListener.OnNavigationItemSelected(IMenuItem item)
   {
      base.OnNavigationItemSelected(item);
      if (App.quizRunning == true)
      {
          _page.CurrentPage = App.navCardsTabPage;
      }
         return true;
   }

   void BottomNavigationView.IOnNavigationItemReselectedListener.OnNavigationItemReselected(IMenuItem item)
   { 
      if (App.quizRunning == true)
      {
          _page.CurrentPage = App.navCardsTabPage;
      }
   }

App.navCardsTabPage 包含用于隐藏和显示选项卡项标题和图标的代码(SetNav 和 ClearNav)。

Answer 1

尝试设置 IsEnabled="false" 属性并查看它是否有效:

更新:

添加一个类 BottomNavTabPageRenderer 这是您的 Android 自定义渲染器

[assembly: ExportRenderer(typeof(BottomNavTabPage), typeof(BottomNavTabPageRenderer))]
namespace Droid.CustomRenderers
{
public class BottomNavTabPageRenderer : TabbedPageRenderer, BottomNavigationView.IOnNavigationItemSelectedListener, BottomNavigationView.IOnNavigationItemReselectedListener
{
    private bool _isShiftModeSet;

    public BottomNavTabPageRenderer( Context context )
        : base(context)
    {

    }

    bool BottomNavigationView.IOnNavigationItemSelectedListener.OnNavigationItemSelected( IMenuItem item )
    {
        if(item.TitleFormatted.ToString().Trim()== "YourTitleString") // Disable based on Title of the item 
        {
            return false;
        }
        if(!(this.Element as BottomNavTabPage).IsPageChangeEnabled) // Disable every tab
        {
            return false;
        }
        return true;
    }

    public void OnNavigationItemReselected( IMenuItem item )
    {

    }

    protected override void OnLayout( bool changed, int l, int t, int r, int b )
    {
        base.OnLayout(changed, l, t, r, b);
        try
        {
            if(!_isShiftModeSet)
            {
                var children = GetAllChildViews(ViewGroup);

                if(children.SingleOrDefault(x => x is BottomNavigationView) is BottomNavigationView bottomNav)
                {
                    bottomNav.SetShiftMode(false, false);
                    _isShiftModeSet = true;
                }
            }
        }
        catch(Exception e)
        {
            Console.WriteLine($"Error setting ShiftMode: {e}");
        }
    }

    private List<View> GetAllChildViews( View view )
    {
        if(!(view is ViewGroup group))
        {
            return new List<View> { view };
        }

        var result = new List<View>();

        for(int i = 0; i < group.ChildCount; i++)
        {
            var child = group.GetChildAt(i);

            var childList = new List<View> { child };
            childList.AddRange(GetAllChildViews(child));

            result.AddRange(childList);
        }

        return result.Distinct().ToList();
    }
 }
}

请注意，在 OnNavigationItemSelected 方法中有两个条件，您可以根据这两个条件设置是否禁用页面中的选项卡。

在您的 PCL 项目中添加底部导航标签页类以用作标签页

 public class BottomNavTabPage : Xamarin.Forms.TabbedPage
{
    public static readonly BindableProperty ShiftingEnabledProperty = BindableProperty.Create(nameof(IsPageChangeEnabled),
                                                                typeof(bool),
                                                                typeof(BottomNavTabPage), false);

    public bool IsPageChangeEnabled
    {
        get { return (bool)GetValue(ShiftingEnabledProperty); }
        set { SetValue(ShiftingEnabledProperty, value); }
    }
    protected override void OnAppearing()
    {
        this.On<Xamarin.Forms.PlatformConfiguration.Android>().SetIsSwipePagingEnabled(IsPageChangeEnabled);
        base.OnAppearing();
    }

    public BottomNavTabPage()
    {            
        this.On<Xamarin.Forms.PlatformConfiguration.Android>().SetToolbarPlacement(ToolbarPlacement.Bottom);
    }
}      

为底部导航 View 添加 Shift 模式，以便它正确显示标签和图标。

 public static void SetShiftMode( this BottomNavigationView bottomNavigationView, bool enableShiftMode, bool enableItemShiftMode )
    {
        try
        {
            var menuView = bottomNavigationView.GetChildAt(0) as BottomNavigationMenuView;
            if(menuView == null)
            {
                System.Diagnostics.Debug.WriteLine("Unable to find BottomNavigationMenuView");
                return;
            }


            var shiftMode = menuView.Class.GetDeclaredField("mShiftingMode");

            shiftMode.Accessible = true;
            shiftMode.SetBoolean(menuView, enableShiftMode);
            shiftMode.Accessible = false;
            shiftMode.Dispose();


            for(int i = 0; i < menuView.ChildCount; i++)
            {
                var item = menuView.GetChildAt(i) as BottomNavigationItemView;
                if(item == null)
                    continue;

                item.SetShiftingMode(enableItemShiftMode);
                item.SetChecked(item.ItemData.IsChecked);

            }

            menuView.UpdateMenuView();
        }
        catch(Exception ex)
        {
            System.Diagnostics.Debug.WriteLine($"Unable to set shift mode: {ex}");
        }
    }

用法:

您可以在 C# 和 XAML 中使用它，如下所示:

C#:

BottomNavTabPage tabbedPage = null;
tabbedPage = new BottomNavTabPage();
tabbedPage.IsPageChangeEnabled=false; // Important for not allowing tab change
var navigationPage = new NavigationPage(new MainPage())
{
  Icon = "icon",
  Title = "Schedule"
};
var navigationPage2 = new NavigationPage(new MainPage())
{
  Icon = "icon",
  Title = "Schedule2"
};

tabbedPage.Children.Add(navigationPage);
tabbedPage.Children.Add(navigationPage2);
this.MainPage= tabbedPage;

XAML

<?xml version="1.0" encoding="utf-8" ?>
<Custom:BottomNavTabPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:Custom="clr-namespace:XamarinCertUnderstanding.CustomControls"             
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"             
         x:Class="XamarinCertUnderstanding.Views.MainPage">
<Custom:TodayPage />
<NavigationPage Title="Schedule" Icon="schedule.png">
    <x:Arguments>
        <Custom:SchedulePage />
    </x:Arguments>
</NavigationPage>
</Custom:BottomNavTabPage>