如何在Xamarin Forms中“重新添加”TabbedPage子项时禁用BottomNavigationView转换模式？

Question

我有一个在BottomNavigationView侧使用Android的XF应用程序，根据用户模式删除并添加TabbedPage孩子。下面是我的Android渲染器：

public class BottomTabPageRenderer : TabbedPageRenderer
{

    public BottomTabPageRenderer(Context context) : base(context) { }

    protected override void OnElementChanged(ElementChangedEventArgs<TabbedPage> e)
    {
        base.OnElementChanged(e);

        if (ViewGroup != null && ViewGroup.ChildCount > 0)
        {
            BottomNavigationMenuView bottomNavigationMenuView = FindChildOfType<BottomNavigationMenuView>(ViewGroup);

            if (bottomNavigationMenuView != null)
            {
                var shiftMode = bottomNavigationMenuView.Class.GetDeclaredField("mShiftingMode");

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

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

                    item.SetShiftingMode(false);
                    item.SetChecked(item.ItemData.IsChecked);
                }

                if (bottomNavigationMenuView.ChildCount > 0) bottomNavigationMenuView.UpdateMenuView();
            }

        }

        T FindChildOfType<T>(ViewGroup viewGroup) where T : Android.Views.View
        {
            if (viewGroup == null || viewGroup.ChildCount == 0) return null;

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

                var typedChild = child as T;
                if (typedChild != null) return typedChild;

                if (!(child is ViewGroup)) continue;

                var result = FindChildOfType<T>(child as ViewGroup);

                if (result != null) return result;
            }

            return null;
        }
   }
}

当用户通过单击按钮启动游戏时，底部的5个选项卡中有4个被删除。当用户通过单击按钮再次结束游戏时，再次添加选项卡。我试过xxx.Children.Insert()将标签放回原来的位置，但这给了我以下错误：

Java.Lang.IndexOutOfBoundsException: Index: 1, Size: 1

所以我最终得到了以下代码：

public static void ReAddChildren()
{
   mainPage.Children.Remove(gameTabPage);
   mainPage.Children.Add(homeTabPage);
   mainPage.Children.Add(helpTabPage);
   mainPage.Children.Add(settingsTabPage);
   mainPage.Children.Add(dictTabPage);
   mainPage.Children.Add(gameTabPage);
 }

这有效，但现在shiftingMode回来了。有人知道每当我“重新添加”标签项时我怎么能禁用它？

Answer 1

Android只是在28.0.0支持库上更新它。不确定Xamarin是否可以访问此本机方法setLabelVisibilityMode（）来禁用转换。

navBottom.setLabelVisibilityMode(LabelVisibilityMode.LABEL_VISIBILITY_LABELED);

Answer 2

在渲染器中，您可以轻松地使用Xamarin.Forms中的此扩展方法来管理移位模式。

https://github.com/xamarin/Xamarin.Forms/blob/master/Xamarin.Forms.Platform.Android/Renderers/BottomNavigationViewUtils.cs

所以你会得到：

using static Xamarin.Forms.Platform.Android.BottomNavigationViewUtils;
public class BottomTabPageRenderer : TabbedPageRenderer
{

    public BottomTabPageRenderer(Context context) : base(context) { }

    protected override void OnElementChanged(ElementChangedEventArgs<TabbedPage> e)
    {
        base.OnElementChanged(e);

        if (ViewGroup != null && ViewGroup.ChildCount > 0)
        {
            BottomNavigationMenuView bottomNavigationMenuView = FindChildOfType<BottomNavigationMenuView>(ViewGroup);

            if (bottomNavigationMenuView != null)
            {
                // use extension method from XF
                bottomNavigationMenuView.SetShiftMode(false, false);
            }

        }

        T FindChildOfType<T>(ViewGroup viewGroup) where T : Android.Views.View
        {
            if (viewGroup == null || viewGroup.ChildCount == 0) return null;

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

                var typedChild = child as T;
                if (typedChild != null) return typedChild;

                if (!(child is ViewGroup)) continue;

                var result = FindChildOfType<T>(child as ViewGroup);

                if (result != null) return result;
            }

            return null;
        }
   }
}

Answer 3

正如Pawel所提到的，您可以轻松使用Xamarin.Forms中的扩展方法来管理shift模式。但是这个对我有用

 public class CustomTabbedPageRenderer : TabbedPageRenderer
{

    public CustomTabbedPageRenderer(Context context) : base(context)
    {
    }

    protected override void OnElementChanged(ElementChangedEventArgs<TabbedPage> e)
    {
        base.OnElementChanged(e);

        if (ViewGroup != null && ViewGroup.ChildCount > 0)
        {
            BottomNavigationView bottomNavigationView = FindChildOfType<BottomNavigationView>(ViewGroup);

            if (bottomNavigationView != null)
            {
                // use extension method from XF
                bottomNavigationView.SetShiftMode(false, false);
            }

        }
    }

    private T FindChildOfType<T>(ViewGroup viewGroup) where T : Android.Views.View
    {
        if (viewGroup == null || viewGroup.ChildCount == 0) return null;

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

            var typedChild = child as T;
            if (typedChild != null) return typedChild;

            if (!(child is ViewGroup)) continue;

            var result = FindChildOfType<T>(child as ViewGroup);

            if (result != null) return result;
        }

        return null;
    }

    protected override void DispatchDraw(Canvas canvas)
    {
        base.DispatchDraw(canvas);
    }


}