Xamarin Android 应用程序上下文为空 [英] Xamarin Android application context is null

问题描述

正如我在标题中所说，这是我的问题.为什么我无法访问班级中的上下文?有什么办法可以在这个类中获取上下文的实例吗?

As I said in the heading, this is my problem. Why can't I access the context in my class? Is there any way I could get the instance of the context in this class?

[Service(Exported = false), IntentFilter(new[] { "com.google.android.c2dm.intent.RECEIVE" })]
class MyGcmListenerService : GcmListenerService
{
    public override void OnMessageReceived(string from, Bundle data)
    {
        string msg = data.GetString("message");

        // the app breaks here
        ShowPopup(msg); 

        Log.Info("GcmLstnrService", "From: " + from);
        Log.Info("GcmLstnrService", "Msg: " + msg);
    }

    private void ShowPopup(string message)
    {
        // the app breaks here
        AlertDialog.Builder builder = new AlertDialog.Builder(Application.Context);

        AlertDialog dialog = builder.Create();
        dialog.SetTitle("Push message");
        dialog.SetMessage(message);
        dialog.SetButton("OK", (sender, e) => { });
        dialog.Show();
    }
}

推荐答案

我使用 Xamarin.Forms 和 MessagingCenter 解决了这个问题.

I resolved this issue with Xamarin.Forms and MessagingCenter.

这是我的服务:

[Service(Exported = false), IntentFilter(new[] { "com.google.android.c2dm.intent.RECEIVE" })]
class MyGcmListenerService : GcmListenerService
{
    public override void OnMessageReceived(string from, Bundle data)
    {
        string msg = data.GetString("message");

        // send a string via Xamarin MessagingCenter
        MessagingCenter.Send<object, string>(this, "ShowAlert", msg);
    }
}

这是我的 PCL App 类构造函数的一部分:

And here's part of my PCL App class constructor:

// subscribe to the messages
MessagingCenter.Subscribe<object, string>(this, "ShowAlert", (s, msg) =>
{
    // run on UI thread
    Device.BeginInvokeOnMainThread(() =>
    {
        MainPage.DisplayAlert("Push message", msg, "OK");
    });
});

这篇关于Xamarin Android 应用程序上下文为空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！