In Xamarin Forms 3.1, when using tabbed page with 4 tabs, how can I prevent “sliding” effect of tab bar on Android?

问题

I have an app with four pages, and I want it to look similar to my (non-Xamarin) iOS app, so to have toolbar at the bottom. Here is my MainPage.xaml file:

<?xml version="1.0" encoding="utf-8" ?>
<TabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
             xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
             xmlns:local="clr-namespace:XaBLE1"
             x:Class="XaBLE1.MainPage"
            Title="Safe-T Sim" HeightRequest="768" WidthRequest="512" 

            BarBackgroundColor="#F1F1F1"
            BarTextColor="Gray"
            xmlns:android="clr-namespace:Xamarin.Forms.PlatformConfiguration.AndroidSpecific;assembly=Xamarin.Forms.Core"
            android:TabbedPage.ToolbarPlacement="Bottom"
            android:TabbedPage.BarItemColor="#666666"
            android:TabbedPage.BarSelectedItemColor="Black"
            >

    <NavigationPage Title="Test" Icon="ElectTest.png"
                    HasNavigationBar="False">
        <x:Arguments>
            <local:TestPage />
        </x:Arguments>
    </NavigationPage>
    <NavigationPage Title="Review" Icon="Review.png"
                    HasNavigationBar="False">
        <x:Arguments>
            <local:ReviewPage />
        </x:Arguments>
    </NavigationPage>
    <NavigationPage Title="Setup" Icon="Gear.png"
                    HasNavigationBar="False">
        <x:Arguments>
            <local:SetupPage />
        </x:Arguments>
    </NavigationPage>
    <NavigationPage Title="Info" Icon="Info.png"
                    HasNavigationBar="False">
        <x:Arguments>
            <local:InfoPage />
        </x:Arguments>
    </NavigationPage>
</TabbedPage>

I don't care for the current look-and-feel on Oreo, which is to make the selected page tab larger and put the title, pushing the other tabs aside and removing the page title.

Is there anyway to disable this behavior, and let it just be 4 tabs. Note that this behavior does not happen if there are 3 tabs -- there is only darkening and slight enlarging of the icon & text, but both are visible.

EDIT: I tried the answer suggested in the comments, but as noted I'm not sure this is trying to solve the same problem, and in any case does not change the behavior.

回答1:

It looks like you are looking for this (not implemented yet) feature: [Enhancement] Implement fixed mode for Bottom Navigation Bar Android (Github)

I could solve it following this James Montemagno tutorial: Removing BottomNavigationView’s Icon Shifting in Xamarin.Android and implementing my own Tabbed Page custom renderer:

using Android.Content;
using Android.Support.Design.Internal;
using Android.Views;
using FixedTabbedPage.Droid.CustomRenderers;
using Xamarin.Forms;
using Xamarin.Forms.Platform.Android;
using Xamarin.Forms.Platform.Android.AppCompat;

[assembly: ExportRenderer(typeof(TabbedPage), typeof(CustomTabbedPageRenderer))]
namespace FixedTabbedPage.Droid.CustomRenderers
{
    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)
            {
                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();
                }
            }
        }

        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;
        }
    }
}

You only have to add this code to your Android solution (refactoring namespaces) and here is the result:

回答2:

For disabling tab swipe you can use PlatformConfiguration in your TabbedPage class

public partial class MyTabbedPage : TabbedPage
{
    public MainTabbedPage ()
    {
        InitializeComponent();
        this.On<Xamarin.Forms.PlatformConfiguration.Android>().SetIsSwipePagingEnabled(false);    
    }
}

if you don't have MyTabbedPage class, add it than your axml file structure would look like this

<?xml version="1.0" encoding="utf-8" ?>
<MyTabbedPage xmlns="http://xamarin.com/schemas/2014/forms"
         xmlns:x="http://schemas.microsoft.com/winfx/2009/xaml"
         x:Class="XaBLE1.MainPage">   
</MyTabbedPage>

回答3:

It looks like, there is a simpler alternative since Android 9.

From James Matemagno's blog

来源：https://stackoverflow.com/questions/51864505/in-xamarin-forms-3-1-when-using-tabbed-page-with-4-tabs-how-can-i-prevent-sli