在 Xamarin Android 中使用 BroadcastReceiver 从通知调用服务方法

Question

我启动服务并创建新线程（下载大文件）。同时我显示一个带有动作的通知（暂停按钮）。 当我按下此按钮“WSTRZYMAJ”时，我想从我的服务中调用 PauseDownload() 方法。我该怎么做？我已经阅读了 BroadcastReceiver，创建这个类，但是如何从 BroadcastReceiver 类的服务中调用方法？

通知屏幕：

我的服务片段：

class DownloadsService : Service
{
    DownloadsBroadcastReceiver receiver;
    Notification.Builder notificationBuilder;
    DownloadsData downloadsData;
    int uniqueNumber = 1000;
    bool isStarted;

    public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
    {
        RegisterReceiver(receiver, new IntentFilter("com.xamarin.example.TEST"));
        downloadsData = JsonConvert.DeserializeObject<DownloadsData>(intent.GetStringExtra("downloadsData"));
        if (isStarted)
            Log.Info("DAMIAN", "Error start service");
        else
        {
            Log.Info("DAMIAN", "Start service");
            DispatchNotificationThatServiceIsRunning(downloadsData.Name, "Started");
            new Thread(new ThreadStart(() =>
            {
                MakeDownload();
            })).Start();
            isStarted = true;
        }
        return StartCommandResult.NotSticky;
    }

    private void DispatchNotificationThatServiceIsRunning(string title, string content)
    {
        Intent stopIntent = new Intent(this, typeof(DownloadsBroadcastReceiver));
        stopIntent.PutExtra("action", "actionName");
        PendingIntent stopPi = PendingIntent.GetBroadcast(this, 4, stopIntent, PendingIntentFlags.UpdateCurrent);
        Intent intent = new Intent(this, typeof(MainActivity));
        TaskStackBuilder stackBuilder = TaskStackBuilder.Create(this);
        stackBuilder.AddParentStack(Java.Lang.Class.FromType(typeof(MainActivity)));
        stackBuilder.AddNextIntent(intent);
        PendingIntent resultPendingIntent = stackBuilder.GetPendingIntent(0, PendingIntentFlags.UpdateCurrent);
        Notification.Action pauseAction = new Notification.Action.Builder(Resource.Drawable.Pause, "WSTRZYMAJ", stopPi).Build();
        notificationBuilder = new Notification.Builder(this)
            .SetSmallIcon(Resource.Drawable.Icon)
            .SetContentIntent(resultPendingIntent)
            .SetContentTitle(title)
            .SetContentText(content)
            .AddAction(pauseAction);
        var notificationManager = (NotificationManager)GetSystemService(NotificationService);
        notificationManager.Notify(uniqueNumber, notificationBuilder.Build());
    }

    private void UpdateNotification(string content)
    {
        notificationBuilder.SetContentText(content);
        var notificationManager = (NotificationManager)GetSystemService(NotificationService);
        notificationManager.Notify(uniqueNumber, notificationBuilder.Build());
    }

    private void MakeDownload()
    {
    //downloading file
    }

    private void PauseDownload()
    {
    //pause downloading
    }
}

以及完整的代码 BroadcastReceiver 类：

[BroadcastReceiver(Enabled = true, Exported = false)]
[IntentFilter(new[] { "com.xamarin.example.TEST" })]
class DownloadsBroadcastReceiver : BroadcastReceiver
{
    public override void OnReceive(Context context, Intent intent)
    {
        String action = intent.GetStringExtra("action");
        if (action.Equals("actionName"))
            Log.Info("DAMIAN", "BROADCAST"); //it works, ie. I have text "BROADCAST" in log
    }
}

Answer 1

如何从 BroadcastReceiver 类的服务中调用方法？

当您收到DownloadsBroadcastReceiver 的消息时，您可以再次启动您的DownloadsService。当你这样做的时候，由于你的DownloadsService已经创建好了，它会调用OnStartCommand()方法，所以你会在这个方法中收到消息，你可以在OnStartCommand()方法中调用PauseDownload()。

这样的用法：

[BroadcastReceiver(Enabled = true, Exported = false)]
[IntentFilter(new[] { "com.xamarin.example.TEST" })]
public class DownloadsBroadcastReceiver : BroadcastReceiver
{
    public override void OnReceive(Context context, Intent intent)
    {
        String action = intent.GetStringExtra("action");
        if ("actionName".Equals(action))
        {
            Intent intent2 = new Intent(Application.Context, typeof(DownloadsService));
            intent2.PutExtra(action, "actionName");

            Application.Context.StartService(intent2);
        }
    }
}

在您的DownloadsService 班级中：

public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
{
     String action = intent.GetStringExtra("action");
     if ("actionName".Equals(action))
     {
        PauseDownload();
     }

     ...
     return StartCommandResult.NotSticky;
}