lementChanged（ElementChangedEventArgs e） { 基础。一个要素发生变化（e）； if（例如NewElement！=null） { tabbedPage=e.NewElement作为Xamarin.Forms.tabbe

lementChanged（ElementChangedEventArgs e） { 基础。一个要素发生变化（e）； if（例如NewElement！=null） { tabbedPage=e.NewElement作为Xamarin.Forms.tabbedPage； bottomNavigationView=（GetChildAt（0）作为Android.Widget.RelativeLayout）。GetChildAt（1）作为bottomNavigationView； bottomNavigationView.NavigationItemSelected+=bottomNavigationView\u NavigationItemSelected； //调用以更改字体 ChangeFont（）； } if（e.OldElement！=null） { bottomNavigationView.NavigationItemSelected-=bottomNavigationView\u NavigationItemSelected； } bottomNavigationView.Visibility=ViewStates.Gone； }

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for info NiftyTabbedPage是TL/DR不合适的简单TabbedPage的子类。我有一个用例正好需要这个功能。我的应用程序有一个主进程，它将页面推到堆栈上，并在进程结束时弹出到根目录。我支持使用根页面上的选项卡访问的功能。对于主进程，选项卡需要隐藏，并且只在根上可见。

// in App.xaml.cs

public App()
{
    InitializeComponent();
    MainPage = new NavigationPage(new FirstPage())
    {
        HasNavigationBar = false;
    };
}

public void Button_OnPress(object sender, EventArgs e)
{
    var navigationPage = Application.Current.MainPage as NavigationPage;
    if(navigationPage != null)
    {
        navigationPage.PushAsync(new WhatEverPage());
    }
}

using System;
using AppoMobi.iOS;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;
using UIKit;

[assembly: ExportRenderer(typeof(TabbedPage), typeof(HiddenTabbedPageRenderer))]
namespace AppoMobi.iOS
{   
    //***************************************************************************
    public class HiddenTabbedPageRenderer : TabbedRenderer
    //***************************************************************************
    {

        private UITabBarController tabbarController { get; set; }
        private TabbedPage CurrentTabbedPage { get; set; }

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

            if (e.OldElement != null)
            {
                //release any stuff here
            }

            if (e.NewElement != null)
            {
                tabbarController = (UITabBarController) this.ViewController;
                CurrentTabbedPage = (TabbedPage) e.NewElement;
            }
            else
            {
                CurrentTabbedPage = (TabbedPage) e.OldElement;
            }

            //the following commented code is not working
            //as Forms as it just leaves empty white space
            //instead of hidden tabbedbar:     
            //       if (tabbarController != null)
            //         tabbarController.TabBar.Hidden = true;
        }

        //just hide tabbar by setting its height to zero
        // credits:
        // https://stackoverflow.com/a/26255545/7149454
        // "how to change UITabBar height"
        private nfloat newHeight = 0; //change tabbed bar height to this value
        //-------------------------------------------------------------------
        public override void ViewWillLayoutSubviews()
        //-------------------------------------------------------------------
        {
            if (tabbarController != null)
            {
                var tabFrame = tabbarController.TabBar.Frame; //self.TabBar is IBOutlet of your TabBar
                tabFrame.Height = newHeight;
                tabFrame.Offset(0, tabbarController.View.Frame.Height - newHeight);
                tabbarController.TabBar.Frame = tabFrame;
            }
            base.ViewWillLayoutSubviews();
        }
    }
}

using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
using System;
using Android.Content;
using Android.Support.Design.Widget;
using Android.Support.V4.View;
using Android.Views;
using AppoMobi.Droid;
using Xamarin.Forms.Platform.Android.AppCompat;

[assembly: ExportRenderer(typeof(TabbedPage), typeof(MyTabbedRenderer))]
namespace AppoMobi.Droid
{
    //****************************************************
    public class MyTabbedRenderer : TabbedPageRenderer, TabLayout.IOnTabSelectedListener
    //****************************************************
    {

        private TabLayout TabsLayout { get; set; }
        private ViewPager PagerLayout { get; set; }
        private NiftyTabbedPage CurrentTabbedPage { get; set; }

        //-------------------------------------------------------------------
        public MyTabbedRenderer(Context context) : base(context)
        //-------------------------------------------------------------------
        {
        }

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

            if (e.OldElement != null)
            {
                //cleanup here
            }

            if (e.NewElement != null)
            {
                CurrentTabbedPage = (NiftyTabbedPage)e.NewElement;
            }
            else
                CurrentTabbedPage = (NiftyTabbedPage)e.OldElement;

            //find the pager and tabs
            for (int i = 0; i < ChildCount; ++i)
            {
                Android.Views.View view = (Android.Views.View)GetChildAt(i);
                if (view is TabLayout)
                    TabsLayout = (TabLayout)view;
                else
                if (view is ViewPager) PagerLayout = (ViewPager)view;
            }

        }


        //-------------------------------------------------------------------------------
        protected override void OnLayout(bool changed, int l, int t, int r, int b)
        //-------------------------------------------------------------------------------    
        {
            TabsLayout.Visibility = ViewStates.Gone;

            base.OnLayout(changed, l, t, r, b);
        }    
    }


}

public class TabControllerPage : TabbedPage
{
    public TabControllerPage()
    {
        // This hides the navigation page's navigation bar as it is not needed
        NavigationPage.SetHasNavigationBar(this, false);

        // Create tab page and pass PushPage action to it
        var testPage = new TestPage {
            PushPage = (page) => {
                Navigation.PushAsync(page, true);
            }
        };

        // Add as many tabs as you like here
        AddTab(testPage, "Tab 1", true, "tab_1_icon.png");
    }

    void AddTab(Page page, string title, bool inNav, string icon = null)
    {
        // This sets the NavigationBar title
        page.Title = title;

        if (inNav)
        {
            var navigationPage = new NavigationPage(page);
            if (icon != null)
            {
                navigationPage.Icon = icon;
            }
            // This sets the tab labels
            navigationPage.Title = title;
            Children.Add(navigationPage);
        }
        else
        {
            Children.Add(page);
        }
    }
}

public partial class TestPage : ContentPage
{
    public Action<ContentPage> PushPage;

    public TestPage()
    {
        InitializeComponent();
    }

    // Call this method when ever you need to push a page onto the navigation page and hide the tabbed page.
    void NavigateToPage(ContentPage page)
    {
        PushPage?.Invoke(page);
    }
}

this.Children.Remove(Page you want to remove);

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

        if (e.NewElement != null)
        {
            tabbedPage = e.NewElement as Xamarin.Forms.TabbedPage;
            bottomNavigationView = (GetChildAt(0) as Android.Widget.RelativeLayout).GetChildAt(1) as BottomNavigationView;
            bottomNavigationView.NavigationItemSelected += BottomNavigationView_NavigationItemSelected;

            //Call to change the font
            ChangeFont();
        }

        if (e.OldElement != null)
        {
            bottomNavigationView.NavigationItemSelected -= BottomNavigationView_NavigationItemSelected;
        }

        bottomNavigationView.Visibility = ViewStates.Gone;
    }