Periodic background task in Blazor wasm

Question

In Blazor wasm, I would like to periodically execute a job (code), even if the user is navigating through the pages (every x min for example).

Is that possible? What would be a practical way?

Answer 1

Create a Service to manage the timer

public class JobExecutedEventArgs : EventArgs {}


public class PeriodicExecutor : IDisposable
{
    public event EventHandler<JobExecutedEventArgs> JobExecuted;
    void OnJobExecuted()
    {
        JobExecuted?.Invoke(this, new JobExecutedEventArgs());
    }

    Timer _Timer;
    bool _Running;

    public void StartExecuting()
    {
        if (!_Running)
        {
            // Initiate a Timer
            _Timer= new Timer();
            _Timer.Interval = 300_000;  // every 5 mins
            _Timer.Elapsed += HandleTimer;
            _Timer.AutoReset = true;
            _Timer.Enabled = true;

            _Running = true;
        }
    }
    void HandleTimer(object source, ElapsedEventArgs e)
    {
        // Execute required job

        // Notify any subscribers to the event
        OnJobExecuted();
    }
    public void Dispose()
    {
        if (_Running)
        {
            // Clear up the timer
        }
    }
}

Register it in Program.cs

builder.Services.AddSingleton<PeriodicExecutor>();

Request it and start it in home page initialization

@page "/home"
@inject PeriodicExecutor PeriodicExecutor

@code {
    protected override void OnInitialized()
    {
        PeriodicExecutor.StartExecuting();
    }
}

In any component if you want to do something when job executes

@inject PeriodicExecutor PeriodicExecutor
@implements IDisposable

<label>@JobNotification</label>

@code {

   protected override void OnIntiialized()
   {
       PeriodicExecutor.JobExecuted += HandleJobExecuted;
   }
   public void Dispose()
   {
       PeriodicExecutor.JobExecuted -= HandleJobExecuted;
   }

   string JobNotification;
   void HandleJobExecuted(object sender, JobExecutedEventArgs e)
   {
        JobNotification = $"Job Executed: {DateTime.Now}";
        StateHasChanged();
   }
}

Answer 2

If you are using an ASP.NET Core Hosted flavor of Blazor WebAssembly, you can use a BackgroundService. For example:

MyBackgroundService.cs

public class MyBackgroundService : BackgroundService
{
    private readonly ILogger<CollectionService> _logger;
    private readonly IServiceScopeFactory _serviceScopeFactory;

    public MyBackgroundService(ILogger<CollectionService> logger, IServiceScopeFactory serviceScopeFactory)
    {
        _logger = logger;
        _serviceScopeFactory = serviceScopeFactory;
    }

    protected override async Task ExecuteAsync(CancellationToken stoppingToken)
    {
        _logger.LogInformation("My Background Service is starting.");

        //Do your work here...

Startup.cs

public void ConfigureServices(IServiceCollection services)
{
    services.AddSingleton<MyBackgroundService>();
    services.AddHostedService(provider => provider.GetService<MyBackgroundService>());

One benefit of this solution is the service will start running regardless of whether a user navigates to any particular page on the site. Or even if no user access the site.