IHostedService/BackgroundService 的生命周期是什么？

在 IHostedService 上调用 StopAsync 后，是否可以在同一实例上再次调用 StartAsync？

- 是的

一个最小的 Blazor 服务器示例：

public class MyBackGroundService : IHostedService, IDisposable
 {
     private readonly ILogger<MyBackGroundService> _log;
     private Timer _timer;

     private int index { get; set; }


     public bool isRunning { get; set; }=false;
     public MyBackGroundService(ILogger<MyBackGroundService> log)
     {
         _log = log;
         index=new Random().Next(0,20);
     }

     public void Dispose()
     {
         _timer.Dispose();
     }

     public Task StartAsync(CancellationToken cancellationToken)
     {
         isRunning=true;
        
         _timer = new Timer(Do, null, TimeSpan.Zero, TimeSpan.FromSeconds(10));
         return Task.CompletedTask;
     }

     public Task StopAsync(CancellationToken cancellationToken)
     {
         isRunning = false;
         _log.LogInformation($"{DateTime.Now} BackService{index} is Stopping");
         _timer?.Change(Timeout.Infinite, 0);
         return Task.CompletedTask;
     }
     private void Do(object o)
     {
         _log.LogInformation($"Background Service{index} is working.  {DateTime.Now}");
         try
         {
             
             // dosometing 
         }
         catch (Exception e)
         {
            
             _log.LogInformation("Error: {0}", e.Message);
             throw e;

         }
     }
 }

在program.cs中：

builder.Services.AddSingleton<MyBackGroundService>();
builder.Services.AddHostedService<MyBackGroundService>();

在剃须刀组件中：

@inject MyBackGroundService backgroundservice;

<PageTitle>Counter</PageTitle>

<button @onclick="start">Start</button>
<button @onclick="stop">Stop</button>




@code {
    protected override void OnInitialized()
    {
        if (backgroundservice.isRunning)
        {
            backgroundservice.StopAsync(new System.Threading.CancellationToken());
        }
        base.OnInitialized();
    }
    public void start()
    {
        if (!backgroundservice.isRunning)
        {
            backgroundservice.StartAsync(new System.Threading.CancellationToken());
        }

    }
    public void stop()
    {
        if (backgroundservice.isRunning)
        {
            backgroundservice.StopAsync(new System.Threading.CancellationToken());
        }

    }
}

注册为单例的可以多次启动和停止，使用AddHostedService方法注册的会在应用启动时启动，在应用关闭时停止

我点击按钮按照步骤：开始——停止——启动，控制台：