定時任務組件，除了 Hangfire 外，還有一個 Quarz.NET，不過 Hangfire .NET Core 支持的會更好些。

ASP.NET Core 使用 Hangfire 很簡單，首先，Nuget 安裝程序包：

> install-package Hangfire -pre

然后ConfigureServices添加配置代碼：

public void ConfigureServices(IServiceCollection services)
{
    services.AddHangfire(x => x.UseSqlServerStorage("<name or connection string>"));
}

上面配置的是 Hangfire 任務配置數據庫信息，默認只支持 SQLServer，如果不想使用數據庫的話，可以 Nuget 安裝程序包：

> install-package Hangfire.MemoryStorage -pre

修改ConfigureServices配置代碼：

public void ConfigureServices(IServiceCollection services)
{
    services.AddHangfire(x => x..UseStorage(new MemoryStorage()));
}

Hangfire 擴展（比如 MySql）：https://www.hangfire.io/extensions.html

然后Configure添加配置代碼：

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    app.UseHangfireServer();
    app.UseHangfireDashboard();

    RecurringJob.AddOrUpdate(() => Console.WriteLine("Recurring!"), Cron.Minutely());
}

上面配置代碼一分鍾執行一次，Hangfire 支持 UI 界面展示，地址：http://localhost:8089/hangfire

Hangfire 默認也支持執行異步方法，RecurringJob方法簽名：

public static void AddOrUpdate<T>(Expression<Func<T, Task>> methodCall, string cronExpression, TimeZoneInfo timeZone = null, string queue = "default");
public static void AddOrUpdate(Expression<Func<Task>> methodCall, string cronExpression, TimeZoneInfo timeZone = null, string queue = "default");
public static void AddOrUpdate<T>(Expression<Func<T, Task>> methodCall, Func<string> cronExpression, TimeZoneInfo timeZone = null, string queue = "default");
public static void AddOrUpdate(Expression<Func<Task>> methodCall, Func<string> cronExpression, TimeZoneInfo timeZone = null, string queue = "default");

異步和同步使用沒有任何區別，示例代碼：

public void Configure(IApplicationBuilder app, IHostingEnvironment env, ILoggerFactory loggerFactory)
{
    app.UseHangfireServer();
    app.UseHangfireDashboard();

    RecurringJob.AddOrUpdate(() => TestAsync(), Cron.Minutely());
}

public static async Task TestAsync()
{
    // to do...
}