.NET Maui Android中Worker.DoWork如何维持事件驱动长时任务运行

问题场景 #

在.NET Maui Android应用中，使用AndroidX.Work.Worker启动监听加速度计事件的长时进程，当前遇到的问题是：一旦DoWork方法退出，Worker就会终止，需要通过阻止DoWork退出来维持Worker运行。

解决方案代码 #

修改DropDetectorWorker类，通过ManualResetEventSlim阻塞DoWork方法，直到主动触发停止信号或Worker被系统终止：

using System.Threading;

public class DropDetectorWorker : AndroidX.Work.Worker
{
    private readonly ManualResetEventSlim _waitEvent = new ManualResetEventSlim(false);
    private readonly DropDetector _dropDetector = new DropDetector();
    private NotificationManager _notificationManager;
    private const string INITIAL_NOTIFICATION_CHANNEL_ID = "drop_detector_channel";
    private const string INITIAL_NOTIFICATION_CHANNEL_NAME = "Drop Detector";
    private static int NotificationId = 1001;

    public DropDetectorWorker(Context context, WorkerParameters workerParams) : base(context, workerParams)
    {
        _notificationManager = (NotificationManager)context.GetSystemService(Context.NotificationService);
    }

    public override Result DoWork()
    {
        CreateInitialNotificationChannel();
        
        var foregroundInfo = new ForegroundInfo(NotificationId++, BuildInitialNotification());
        SetForegroundAsync(foregroundInfo).Wait();
        
        InitialiseDropDetector();
        
        // 阻塞DoWork方法，直到_waitEvent被触发
        _waitEvent.Wait();
        
        // 清理资源
        _dropDetector.DropDetected -= DropDetector_DropDetected;
        _dropDetector.Stop();
        
        return Result.InvokeSuccess();
    }

    private void InitialiseDropDetector()
    {
        _dropDetector.DropDetected += DropDetector_DropDetected;
        _dropDetector.Start();
    }

    private void DropDetector_DropDetected(object sender, DropDetectedEventArgs e)
    {
        var lastDropDetected = DateTime.UtcNow;
        TriggerAutoclaimNotification(e.Magnitude);
        
        // 若需在某次检测后停止Worker，可在此调用：_waitEvent.Set();
    }

    private void CreateInitialNotificationChannel()
    {
        if (_notificationManager.GetNotificationChannel(INITIAL_NOTIFICATION_CHANNEL_ID) != null)
            return;
            
        NotificationChannel channel = new(INITIAL_NOTIFICATION_CHANNEL_ID, INITIAL_NOTIFICATION_CHANNEL_NAME, NotificationImportance.Default)
        {
            LightColor = Microsoft.Maui.Graphics.Color.FromRgba(0, 0, 255, 255).ToInt(),
            LockscreenVisibility = NotificationVisibility.Public
        };
    
        _notificationManager.CreateNotificationChannel(channel);
    }

    private Notification BuildInitialNotification()
    {
        return new Notification.Builder(Context, INITIAL_NOTIFICATION_CHANNEL_ID)
            .SetContentTitle("Drop Detector Running")
            .SetContentText("Listening for drop events")
            .SetSmallIcon(Resource.Drawable.ic_notification)
            .Build();
    }

    private Notification BuildMakeClaimNotification(double magnitude)
    {
        return new Notification.Builder(Context, INITIAL_NOTIFICATION_CHANNEL_ID)
            .SetContentTitle("Drop Detected!")
            .SetContentText($"Magnitude: {magnitude:F2}")
            .SetSmallIcon(Resource.Drawable.ic_notification_alert)
            .Build();
    }

    private void TriggerAutoclaimNotification(double magnitude)
    {
        var foregroundInfo = new ForegroundInfo(NotificationId++, BuildMakeClaimNotification(magnitude));
        SetForegroundAsync(foregroundInfo).Wait();
    }

    public override void OnStopped()
    {
        // 系统停止Worker时，触发信号解除阻塞
        _waitEvent.Set();
        base.OnStopped();
    }
}

关键说明 #

• 用ManualResetEventSlim实现阻塞：DoWork末尾调用_waitEvent.Wait()，会一直阻塞直到_waitEvent.Set()被触发。
• 处理系统终止场景：重写OnStopped方法，当系统主动停止Worker时，触发信号让DoWork退出并清理资源。
• 资源清理：退出前移除事件订阅、停止检测器，避免内存泄漏。
• 前台服务确保稳定：调用SetForegroundAsync时用.Wait()，保证前台服务设置完成后再启动监听。
• 按需停止Worker：如果需要在某次掉落检测后终止任务，可在DropDetector_DropDetected事件中调用_waitEvent.Set()。

内容的提问来源于stack exchange，提问作者Netricity