Xamarin.Android体系结构组件:无法获取生命周期事件的回调 [英] Xamarin.Android Architecture Components: Not getting callbacks for lifecycle events

问题描述

我正在尝试使用体系结构组件包来检测应用程序何时进入后台或前台状态.问题是没有调用回调.在下面的示例代码中，未调用方法onApplicationForegrounded和onApplicationBackgrounded:

I'm trying to use the architecture components package for detecting when the application enters background or foreground state. The problem is that the callbacks are not being invoked. In the sample code below, the methods onApplicationForegrounded and onApplicationBackgrounded are not invoked:

namespace POC.Droid
{
    [Application]
    public class MyApp : Application, ILifecycleObserver
    {
        static readonly string TAG = "MyApp";

        public MyApp(IntPtr handle, Android.Runtime.JniHandleOwnership ownerShip) : base(handle, ownerShip)
        {
        }

        public override void OnCreate()
        {
            base.OnCreate();
            ProcessLifecycleOwner.Get().Lifecycle.AddObserver(this);
        }

        [Lifecycle.Event.OnStop]
        public void onAppBackgrounded()
        {
            Log.Debug(TAG, "App entered background state.");
        }

        [Lifecycle.Event.OnStart]
        public void onAppForegrounded()
        {
            Log.Debug(TAG, "App entered foreground state.");
        }
    }
}

我的Xamarin版本是8.2.0.16(Visual Studio社区)，而Xamarin.Android.Arch.Lifecycle.Extensions版本是1.0.0.我正在使用Nougat设备(7.0)进行测试.

My Xamarin version is 8.2.0.16 (Visual Studio Community) and Xamarin.Android.Arch.Lifecycle.Extensions version is 1.0.0. I'm using a Nougat device (7.0) for testing.

推荐答案

TL; DR请用[Export]

这里有更详细的描述:

通常，要调用生命周期观察器的方法，请确保存在相关的软件包.这是我的packages.config的一部分:

Generally, to get the methods of a lifecycle observer be invoked, please make sure that the related packages are present. Here is a part of my packages.config:

<?xml version="1.0" encoding="utf-8"?>
<packages>
  <package id="Xamarin.Android.Arch.Core.Common" version="26.1.0" targetFramework="monoandroid81" />
  <package id="Xamarin.Android.Arch.Core.Runtime" version="1.0.0.1" targetFramework="monoandroid81" />
  <package id="Xamarin.Android.Arch.Lifecycle.Common" version="26.1.0" targetFramework="monoandroid81" />
  <package id="Xamarin.Android.Arch.Lifecycle.Extensions" version="1.0.0.1" targetFramework="monoandroid81" />
  <package id="Xamarin.Android.Arch.Lifecycle.Runtime" version="1.0.3.1" targetFramework="monoandroid81" />

这是在Visual Studio中的外观:

This is how this looks in Visual Studio:

要能够设置生命周期观察者，我们需要一个生命周期所有者.在应用程序级别，它可以是ProcessLifecycleOwner，就像原始海报所示.

To be able to set a lifecycle observer, we need a lifecycle owner. On the application level this can be ProcessLifecycleOwner, just like the original poster showed.

这里是一个稍作修改的版本:

Here is a slightly modified version:

using System;
using Android.App;
using Android.Arch.Lifecycle;
using Android.Util;
using Java.Interop;

namespace Stopwatch_AAC
{
    [Application]
    public class MyApp : Application, ILifecycleObserver
    {
        const string TAG = "MyApp";

        public MyApp(IntPtr handle, Android.Runtime.JniHandleOwnership ownerShip) : base(handle, ownerShip)
        {
        }

        public override void OnCreate()
        {
            base.OnCreate();
            ProcessLifecycleOwner.Get().Lifecycle.AddObserver(this);
        }

        [Lifecycle.Event.OnStop]
        [Export]
        public void Stopped()
        {
            Log.Debug(TAG, "App entered background state.");
        }

        [Lifecycle.Event.OnStart]
        [Export]
        public void Started()
        {
            Log.Debug(TAG, "App entered foreground state.");
        }
    }
}

如您所见，您可以使用例如[Lifecycle.Event.OnStop]注释生命周期方法.另外，请注意，您需要使用[Export].请确保在项目中引用了Mono.Android.Export，如以下屏幕截图所示.

As you can see, you annotate your lifecycle methods with for example [Lifecycle.Event.OnStop]. Also, please note that you need to use [Export]. Please make sure that Mono.Android.Export is referenced in your project as shown in the following screenshot.

如果您想要活动的生命周期观察者，我建议扩展AppCompatActivity，因为它是生命周期所有者:

If you want to have lifecycle observers for an activity, I suggest to extend AppCompatActivity as it is a lifecycle owner:

using Android.App;
using Android.Arch.Lifecycle;
using Android.OS;
using Android.Support.V7.App;
using Android.Util;
using Java.Interop;

namespace Stopwatch_AAC
{

    [Activity(Label = "Minimal", Exported = true, MainLauncher = true)]
    public class Minimal : AppCompatActivity, ILifecycleObserver
    {
        const string TAG = "Stopwatch_AAC";

        protected override void OnCreate(Bundle savedInstanceState)
        {
            base.OnCreate(savedInstanceState);
            Lifecycle.AddObserver(this);
            Log.Debug(TAG, Lifecycle.CurrentState.ToString());
        }

        [Lifecycle.Event.OnAny]
        [Export]
        public void Hello()
        {
            Log.Debug(TAG, Lifecycle.CurrentState.ToString());
        }
    }
}

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