.NET MAUI Blazor Android前台服务：_subscriberService.Subscribe()始终返回null

在.NET MAUI Blazor Android应用中实现前台服务时，调用_subscriberService.Subscribe()始终返回null，排查所有代码后仍未定位问题。相关实现代码如下：

1. 创建服务 #

[Service]
public class IoTHubService : Service
{
    private readonly ISubscriberService _subscriberService;

    public IoTHubService(ISubscriberService subscriberService)
    {
        _subscriberService = subscriberService;
    }

    public IoTHubService()
    {

    }

    public override IBinder OnBind(Intent intent)
    {
        return null;
    }

    public override StartCommandResult OnStartCommand(Intent intent, StartCommandFlags flags, int startId)
    {
        // 创建前台服务通知
        CreateNotificationChannel();
        var notification = CreateNotification();
        StartForeground(10001, notification);

        // 服务逻辑开始
        // IOTHUB 监听器从此处启动

        _subscriberService.Subscribe();

        return StartCommandResult.Sticky;
    }


    private void CreateNotificationChannel()
    {
        if (Build.VERSION.SdkInt < BuildVersionCodes.O)
        {
            return;
        }

        var channelName = "PROXIWASH 服务";
        var channelDescription = "PROWIWASH 服务通道";
        var channel = new NotificationChannel("10000", channelName, NotificationImportance.Default)
        {
            Description = channelDescription
        };

        var notificationManager = (NotificationManager)GetSystemService(NotificationService);
        notificationManager.CreateNotificationChannel(channel);
    }

    private Notification CreateNotification()
    {
        var notificationBuilder = new NotificationCompat.Builder(this, "10000")
            .SetContentTitle("PROXIWASH 服务")
            .SetContentText("服务运行中")
            .SetSmallIcon(Resource.Drawable.caricon24x)
            .SetOngoing(true);

        return notificationBuilder.Build();
    }
}

2. 包含Start()方法的ForegroundServiceManager #

public class ForegroundServiceManager : IForegroundServiceManager
{
    private readonly IServiceProvider _serviceProvider;

    public ForegroundServiceManager(IServiceProvider serviceProvider)
    {
        _serviceProvider = serviceProvider;
    }

    public void Start()
    {
        try
        {
            // 从依赖注入容器获取ISubscriberService实例
            ISubscriberService subscriberService = _serviceProvider.GetRequiredService<ISubscriberService>();

            // 将subscriberService实例传递给IoTHubService构造函数
            IoTHubService ioTHubService = new IoTHubService(subscriberService);


            var intent = new Intent(MauiApplication.Current.ApplicationContext, typeof(IoTHubService));
            if (Build.VERSION.SdkInt >= BuildVersionCodes.O)
            {
                MauiApplication.Current.ApplicationContext.StartForegroundService(intent);
            }
            else
            {
                MauiApplication.Current.ApplicationContext.StartService(intent);
            }
        }
        catch (Exception ex)
        {
            // 处理异常
        }

    }
}

3. 在MauiProgram.cs中注册服务 #

builder.Services.AddSingleton<IoTHubService>();
builder.Services.AddSingleton<IForegroundServiceManager,ForegroundServiceManager>();
builder.Services.AddSingleton<ISubscriberService, SubscriberService>();
builder.Services.AddSingleton<IOperasyonService, OperasyonService>();

4. 执行数据库与MQTT异步操作的Subscriber Service #

public class SubscriberService : ISubscriberService
{
    private MqttFactory _mqttFactory;
    private IMqttClient _client;
    private IOperasyonService _operasyonService;

    public SubscriberService(IOperasyonService operasyonService)
    {
        _operasyonService = operasyonService;
        _mqttFactory = new MqttFactory();
    }

    public async Task Subscribe()
    {
        // 执行数据库和MQTT服务器相关操作...

        return Task.CompletedTask;
    }
}

5. 在Razor组件中注入IForegroundService并调用Start() #

@inject IForegroundServiceManager _foregroundService

....
protected override void OnInitialized()
{
   _foregroundService.Start();
}

内容的提问来源于stack exchange，提问作者N. OZER SENOL