如何在 Xamarin.Forms 中推送时隐藏标签栏? [英] How to hide Tab Bar on push in Xamarin.Forms?

问题描述

最近几天我一直在使用 iOS 上 Xamarin.Forms 中的 TabbedPage.我找到了一些类似的解决方案:

I'm struggling for last few days with TabbedPage in Xamarin.Forms on iOS. I found some solutions like those: https://forums.xamarin.com/discussion/20901/hide-tab-bar-on-push

However, none of them works well. I also tried to subclass TabbedRenderer and set TabBar height to 0. It works, but if I hide TabBar in NavigationPage.Pushed event handler, there's some delay and for example TableView has blank space on the bottom.

If I try to override NavigationRenderer and hide/show Tab Bar in PushViewController/PopViewController methods it sometimes fails. For example if I navigate fast back and forth, method PopViewController is not invoked, NavigationStack is broken and Tab Bar is not restored.

I think that the only good solution would be to make this property work: UIViewController.HidesBottomBarWhenPushed. However, I have no idea how to do it, because setting/overriding it in renderers doesn't work.

Did anybody manage to successfuly show & hide TabBar?

解决方案

I managed to implement a solution which fixes the issue with blank space after hiding TabBar. You can read more details about it in this article.

To solve the problem we just need to layout all ChildViewControllers. Here is my sample implementation of a custom TabbedPage and its TabbedPageRenderer.

HideableTabbedPage.cs:

using System;
using Xamarin.Forms;

namespace HideTabBar.Controls
{
    public class HideableTabbedPage : TabbedPage
    {
        public static readonly BindableProperty IsHiddenProperty =
            BindableProperty.Create(nameof(IsHidden), typeof(bool), typeof(HideableTabbedPage), false);

        public bool IsHidden
        {
            get { return (bool)GetValue(IsHiddenProperty); }
            set { SetValue(IsHiddenProperty, value); }
        }
    }
}

HideableTabbedPageRenderer.cs:

using System;
using System.ComponentModel;
using System.Threading.Tasks;
using HideTabBar.Controls;
using HideTabBar.iOS.CustomRenderer;
using UIKit;
using Xamarin.Forms;
using Xamarin.Forms.Platform.iOS;

[assembly: ExportRenderer(typeof(HideableTabbedPage), typeof(HideableTabbedPageRenderer))]
namespace HideTabBar.iOS.CustomRenderer
{
    public class HideableTabbedPageRenderer : TabbedRenderer
    {
        private bool disposed;
        private const int TabBarHeight = 49;

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

            if (e.OldElement == null)
            {
                this.Tabbed.PropertyChanged += Tabbed_PropertyChanged;
            }
        }

        private void Tabbed_PropertyChanged(object sender, PropertyChangedEventArgs e)
        {
            if (e.PropertyName == HideableTabbedPage.IsHiddenProperty.PropertyName)
            {
                this.OnTabBarHidden((this.Element as HideableTabbedPage).IsHidden);
            }
        }

        protected override void Dispose(bool disposing)
        {
            base.Dispose(disposing);
            this.disposed = true;
        }

        private async void OnTabBarHidden(bool isHidden)
        {
            if (this.disposed || this.Element == null || this.TabBar == null)
            {
                return;
            }

            await this.SetTabBarVisibility(isHidden);
        }

        private async Task SetTabBarVisibility(bool hide)
        {
            this.TabBar.Opaque = false;
            if (hide)
            {
                this.TabBar.Alpha = 0;
            }

            this.UpdateFrame(hide);

            // Show / Hide TabBar
            this.TabBar.Hidden = hide;
            this.RestoreFonts();

            // Animate appearing 
            if (!hide)
            {
                await UIView.AnimateAsync(0.2f, () => this.TabBar.Alpha = 1);
            }
            this.TabBar.Opaque = true;

            this.ResizeViewControllers();
            this.RestoreFonts();
        }

        private void UpdateFrame(bool isHidden)
        {
            var tabFrame = this.TabBar.Frame;
            tabFrame.Height = isHidden ? 0 : TabBarHeight;
            this.TabBar.Frame = tabFrame;
        }

        private void RestoreFonts()
        {
            // Workaround to restore custom fonts:

            foreach (var item in this.TabBar.Items)
            {
                var text = item.Title;
                item.Title = "";
                item.Title = text;
            }
        }

        private void ResizeViewControllers()
        {
            foreach (var child in this.ChildViewControllers)
            {
                child.View.SetNeedsLayout();
                child.View.SetNeedsDisplay();
            }
        }
    }
}  

Final result:

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