ASP.NET MVC Futures 異步 Action 官方實現使用指南

準備工作

1. 引用 Microsoft.Web.Mvc.dll (Futures 程序集)
2. 路由註冊改用 MapAsyncRoute
3. Controller 繼承 AsyncController

// Global.asax
routes.MapAsyncRoute(
    "Default", 
    "{controller}/{action}/{id}", 
    new { controller = "Home", action = "Index", id = "" }
);

// Controller
public class HomeController : AsyncController { }

模式一：Action / ActionCompleted 配對

// 請求 /Home/Async1
public void Async1() {
    AsyncManager.OutstandingOperations.Increment();
    Task.Run(() => {
        // 異步邏輯
        var data = _repo.GetData();
        AsyncManager.Parameters["data"] = data;
        AsyncManager.OutstandingOperations.Decrement();
    });
}

public ActionResult Async1Completed() {
    var data = AsyncManager.Parameters["data"] as MyData;
    return View(data); // 或 Json(data), Content(...)
}

模式二：Action / ActionCompleted 帶參數

public void Async2(int id) {
    AsyncManager.OutstandingOperations.Increment();
    _service.BeginGetDetail(id, ar => {
        var result = _service.EndGetDetail(ar);
        AsyncManager.Parameters["detail"] = result;
        AsyncManager.OutstandingOperations.Decrement();
    }, null);
}

public ActionResult Async2Completed(DetailModel detail) {
    // 參數自動從 AsyncManager.Parameters 綁定
    return View(detail);
}

模式三：委托模式

[AsyncTimeout(5000)] // 超時屬性
[NoAsyncTimeout] // 禁用超時
public ActionResult Async3() {
    return AsyncManager.Async(() => {
        return _service.GetReport(); // 返回 ActionResult
    });
}

關鍵類型速查

避坑指南

• 必須成對實現 Action + ActionCompleted，否則 404
• AsyncManager.Parameters 僅在單次請求內有效，勿跨請求存儲
• 異常處理：在 Completed 中 try-catch，或重寫 OnException
• Session 訪問：異步線程中無 HttpContext，需主線程預取