xamarin.forms - Xamarin 表单 : How to make tabs on bottom of the page?

Question

我正在寻找位于页面底部的选项卡。我试过 xamarin forms TabbedPage , 但对于 ios 只有标签位于底部和 安卓和windows 选项卡显示在顶部。有什么办法可以实现这个功能吗？

Answer 1

编辑 :对于新的 Xamarin.Forms 项目，您应该使用 Xamarin.Forms Shell ，它提供了简单的选项卡和其他强大的功能。
要做到这一点，您有 3 个选择:
1) 若要使用新的底部标签栏 native 控件，您必须拥有 Xamarin Forms 3.1 或更高版本。
在您的标签页上，您需要为底部放置添加 android 规范:
XAML

<?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:android="clr-namespace:Xamarin.Forms.PlatformConfiguration.AndroidSpecific;assembly=Xamarin.Forms.Core"
    android:TabbedPage.ToolbarPlacement="Bottom"
    x:Class="YouProjectNameSpace.MyTabbedPage">
</TabbedPage>

或者后面的c#代码

using System;
using Xamarin.Forms.PlatformConfiguration;
using Xamarin.Forms.PlatformConfiguration.AndroidSpecific;
using Xamarin.Forms;

namespace YouProjectNameSpace
{
    public partial class MyTabbedPage : TabbedPage
    {
        public MyTabbedPage()
        {
            InitializeComponent();
            On<Android>().SetToolbarPlacement(ToolbarPlacement.Bottom);
        }
    }
}

如果您想要更多自定义，您可以添加:

<?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:android="clr-namespace:Xamarin.Forms.PlatformConfiguration.AndroidSpecific;assembly=Xamarin.Forms.Core"
    android:TabbedPage.ToolbarPlacement="Bottom"
    BarBackgroundColor="#2196F3"
    BarTextColor="White"
    android:TabbedPage.BarItemColor="#66FFFFFF"
    android:TabbedPage.BarSelectedItemColor="White"
    x:Class="YouProjectNameSpace.MyTabbedPage">
</TabbedPage>

2) 为标签页的Android创建一个自定义渲染器并将其移动到底部

using System;
using Xamarin.Forms;

namespace YouProjectNameSpace
{
    public class CustomTabbedPage : TabbedPage
    {
    }
}

和渲染器:

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

[assembly: ExportRenderer(typeof(CustomTabbedPage), typeof(CustomTabbedPageRenderer))]
namespace YouProjectNameSpace.Android
{
    public class CustomTabbedPageRenderer : TabbedPageRenderer
    {
        public CustomTabbedPageRenderer(Context context): base(context)
        {
        }

        protected override void OnLayout(bool changed, int l, int t, int r, int b)
        {
            this.InvertLayoutThroughScale();

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

        private void InvertLayoutThroughScale()
        {
            this.ViewGroup.ScaleY = -1;

            TabLayout tabLayout = null;
            ViewPager viewPager = null;

            for (int i = 0; i < ChildCount; ++i)
            {
                Android.Views.View view = GetChildAt(i);
                if (view is TabLayout tabs)
                    tabLayout = tabs;
                else if (view is ViewPager pager)
                    viewPager = pager;
            }

            tabLayout.ViewTreeObserver.AddOnGlobalLayoutListener(new GlobalLayoutListener(viewPager, tabLayout));

            tabLayout.ScaleY = viewPager.ScaleY = -1;
        }

        private class GlobalLayoutListener : Java.Lang.Object, Android.Views.ViewTreeObserver.IOnGlobalLayoutListener
        {
            private readonly ViewPager viewPager;
            private readonly TabLayout tabLayout;

            public GlobalLayoutListener(ViewPager viewPager, TabLayout tabLayout)
            {
                this.viewPager = viewPager;
                this.tabLayout = tabLayout;
            }

            public void OnGlobalLayout()
            {
                this.viewPager.SetPadding(0, -this.tabLayout.MeasuredHeight, 0, 0);
                this.tabLayout.ViewTreeObserver.RemoveOnGlobalLayoutListener(this);
            }
        }
    }
}

3) 使用特定的库，如 PXTabs ，这将创建一个完整的 Xamarin Forms 底部选项卡，无需任何 native 代码。
如果您想阅读有关底部选项卡和渲染器的更多信息:
Setting TabbedPage Toolbar Placement and Color
Xamarin.Forms: Official Bottom Navigation/Bottom Tabs on Android
BottomNavigationBarXF