c# - 如何在 Xamarin Forms Android 中隐藏时禁用单击 TabbedPage 菜单项？

Question

我有一个 XF 应用程序，TabbedPage当用户处于测验模式时隐藏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，但它们仍然是可点击的。有没有办法在 Xamarin.Android 中禁用此单击事件？我找不到任何关于此的文章/帖子。任何帮助表示赞赏。

编辑：

我BottomNavigationView用来将标签菜单放在底部。

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具有隐藏和显示选项卡项目标题和图标（SetNav和ClearNav）的代码。

标签： c#xamarinxamarin.formsxamarin.android

Answer 1

尝试设置IsEnabled="false"属性，看看它是否有效：

更新：

添加一个类BottomNavTabPageRenderer，它是您的 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，该OnNavigationItemSelected方法中有两个条件，您可以根据这些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);
    }
}      

为底部导航视图添加 Shift 模式，以便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>