如何在 Xamarin Forms 中处理/取消导航 [英] How to handle/cancel back navigation in Xamarin Forms
问题描述
我试图通过覆盖 OnBackButtonPressed 来使用后退导航，但不知何故它根本没有被调用.我正在使用 ContentPage 和最新的 1.4.2 版本.
I tried to use the back navigation by overriding OnBackButtonPressed, but somehow it wasn't get called at all. I am using the ContentPage and the latest 1.4.2 release.
推荐答案
好吧，经过几个小时我想出了这个.它分为三个部分.
Alright, after many hours I figured this one out. There are three parts to it.
#1 处理 android 上的硬件后退按钮.这个很简单，重写 OnBackButtonPressed.请记住，这仅适用于硬件后退按钮和 android.它不会处理导航栏后退按钮.如您所见，我试图在退出页面之前通过浏览器进行返回，但您可以放入任何您需要的逻辑.
#1 Handling the hardware back button on android. This one is easy, override OnBackButtonPressed. Remember, this is for a hardware back button and android only. It will not handle the navigation bar back button. As you can see, I was trying to back through a browser before backing out of the page, but you can put whatever logic you need in.
protected override bool OnBackButtonPressed()
{
if (_browser.CanGoBack)
{
_browser.GoBack();
return true;
}
else
{
//await Navigation.PopAsync(true);
base.OnBackButtonPressed();
return true;
}
}
#2 iOS 导航返回按钮.这个真的很棘手，如果你环顾网络，你会发现一些用新的自定义按钮替换后退按钮的例子，但几乎不可能让它看起来像你的其他页面.在这种情况下，我制作了一个位于普通按钮顶部的透明按钮.
#2 iOS navigation back button. This one was really tricky, if you look around the web you'll find a couple examples of replacing the back button with a new custom button, but it's almost impossible to get it to look like your other pages. In this case I made a transparent button that sits on top of the normal button.
[assembly: ExportRenderer(typeof(MyAdvantagePage), typeof
(MyAdvantagePageRenderer))]
namespace Advantage.MyAdvantage.MobileApp.iOS.Renderers
{
public class MyAdvantagePageRenderer : Xamarin.Forms.Platform.iOS.PageRenderer
{
public override void ViewWillAppear(bool animated)
{
base.ViewWillAppear(animated);
if (((MyAdvantagePage)Element).EnableBackButtonOverride)
{
SetCustomBackButton();
}
}
private void SetCustomBackButton()
{
UIButton btn = new UIButton();
btn.Frame = new CGRect(0, 0, 50, 40);
btn.BackgroundColor = UIColor.Clear;
btn.TouchDown += (sender, e) =>
{
// Whatever your custom back button click handling
if (((MyAdvantagePage)Element)?.
CustomBackButtonAction != null)
{
((MyAdvantagePage)Element)?.
CustomBackButtonAction.Invoke();
}
};
NavigationController.NavigationBar.AddSubview(btn);
}
}
}
Android，很棘手.在旧版本和未来版本的表单中，一旦修复，您可以像这样简单地覆盖 OnOptionsItemselected
Android, is tricky. In older versions and future versions of Forms once fixed, you can simply override the OnOptionsItemselected like this
public override bool OnOptionsItemSelected(IMenuItem item)
{
// check if the current item id
// is equals to the back button id
if (item.ItemId == 16908332)
{
// retrieve the current xamarin forms page instance
var currentpage = (MyAdvantagePage)
Xamarin.Forms.Application.
Current.MainPage.Navigation.
NavigationStack.LastOrDefault();
// check if the page has subscribed to
// the custom back button event
if (currentpage?.CustomBackButtonAction != null)
{
// invoke the Custom back button action
currentpage?.CustomBackButtonAction.Invoke();
// and disable the default back button action
return false;
}
// if its not subscribed then go ahead
// with the default back button action
return base.OnOptionsItemSelected(item);
}
else
{
// since its not the back button
//click, pass the event to the base
return base.OnOptionsItemSelected(item);
}
}
但是，如果您使用的是 FormsAppCompatActivity，那么您需要在 MainActivity 中的 OnCreate 中添加这个来设置您的工具栏:
However, if you are using FormsAppCompatActivity, then you need to add onto your OnCreate in MainActivity this to set your toolbar:
Android.Support.V7.Widget.Toolbar toolbar = this.FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
SetSupportActionBar(toolbar);
但是等等！如果您的 .Forms 版本太旧或版本太新，则会出现工具栏为空的错误.如果发生这种情况，我让它工作以制定最后期限的方式是这样的.在 MainActivity 中的 OnCreate 中:
But wait! If you have too old a version of .Forms or too new version, a bug will come up where toolbar is null. If this happens, the hacked together way I got it to work to make a deadline is like this. In OnCreate in MainActivity:
MobileApp.Pages.Articles.ArticleDetail.androdAction = () =>
{
Android.Support.V7.Widget.Toolbar toolbar = this.FindViewById<Android.Support.V7.Widget.Toolbar>(Resource.Id.toolbar);
SetSupportActionBar(toolbar);
};
ArticleDetail 是一个页面，而 androidAction 是一个 Action，如果我的页面上的平台是 Android，我会在 OnAppearing 上运行.至此，您的应用中的工具栏将不再为空.
ArticleDetail is a Page, and androidAction is an Action that I run on OnAppearing if the Platform is Android on my page. By this point in your app, toolbar will no longer be null.
再加上几个步骤，我们在上面制作的 iOS 渲染使用了您需要添加到您正在为其制作渲染器的任何页面的属性.我正在为我制作的 MyAdvantagePage 类制作它，该类实现了 ContentPage .所以在我的 MyAdvantagePage 类中我添加了
Couple more steps, the iOS render we made above uses properties that you need to add to whatever page you are making the renderer for. I was making it for my MyAdvantagePage class that I made, which implements ContentPage . So in my MyAdvantagePage class I added
public Action CustomBackButtonAction { get; set; }
public static readonly BindableProperty EnableBackButtonOverrideProperty =
BindableProperty.Create(
nameof(EnableBackButtonOverride),
typeof(bool),
typeof(MyAdvantagePage),
false);
/// <summary>
/// Gets or Sets Custom Back button overriding state
/// </summary>
public bool EnableBackButtonOverride
{
get
{
return (bool)GetValue(EnableBackButtonOverrideProperty);
}
set
{
SetValue(EnableBackButtonOverrideProperty, value);
}
}
现在一切都完成了，我可以在我的任何 MyAdvantagePage 上添加这个
Now that that is all done, on any of my MyAdvantagePage I can add this
:
this.EnableBackButtonOverride = true;
this.CustomBackButtonAction = async () =>
{
if (_browser.CanGoBack)
{
_browser.GoBack();
}
else
{
await Navigation.PopAsync(true);
}
};
这应该是让它在 Android 硬件上工作的一切，并为 android 和 iOS 导航回来.
That should be everything to get it to work on Android hardware back, and navigation back for both android and iOS.
这篇关于如何在 Xamarin Forms 中处理/取消导航的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！
