ASP.NET WebForm中用async/await实现异步

1. 在.aspx中添加异步标记

<%@ Page Language="C#" Async="true"%>

2. 在.aspx.cs或者.ascx.cs（用户控件）中添加异步方法

private async Task GetMyPosts()
{
    var posts = await ServiceFactory.BlogPostSevice.GetBlogPostsPagedAsync();
    rpPosts.DataSource = posts;
    rpPosts.DataBind();
}

3. 在.aspx.cs或者.ascx.cs的Page_Load或者OnLoad注册异步方法

protected void Page_Load(object sender, EventArgs e)
{
    this.Page.RegisterAsyncTask(new PageAsyncTask(GetMyPosts));
}

搞定！ 

【参考资料】

How to create Asynchronous device Page in ASP.NET 4.5

from : http://www.cnblogs.com/dudu/p/aspnet-webform-async.html

不要在 ASP.NET 4.5 Beta 的 Page 类事件上直接使用 async 与 await

下面代码中的这种用法是错误的：

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protected async void Page_Load(object sender, EventArgs e) {     WebClient client = new WebClient();     var result1 = await client.DownloadStringTaskAsync("http://www.website.com");     WebClient client2 = new WebClient();     var result2 = await client.DownloadStringTaskAsync(result1);     //do more }

在事件上直接使用 async 引发的错误

目前正确的写法
首先，建议把 UseTaskFriendlySynchronizationContext 设置为 true。

另外，正确的写法如下：

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public partial class WebForm1 : System.Web.UI.Page
{
    protected string Msg { get; set; }
    protected void Page_Load(object sender, EventArgs e)
    {
        RegisterAsyncTask(new PageAsyncTask(Method1));
 
    }
    private async Task Method1()
    {
        using (WebService service = new WebService())
        {
            Msg = await service.HelloWorldTaskSync();
        }
    }
 
    protected void Button_Test_Click(object sender, EventArgs e)
    {
        RegisterAsyncTask(new PageAsyncTask(Method2));
    }
 
    private async Task Method2()
    {
        using (WebService service = new WebService())
        {
            Msg = await service.HelloWorldTaskSync();
        }
    }
}
如果需要写异步，一定要用 RegisterAsyncTask 方法，实测证明，支持多次调用，而且会按次序执行。

from:http://www.cnblogs.com/dozer/archive/2012/03/14/async-and-await-in-asp-net-beta.html

参考资料：

http://stackoverflow.com/questions/9562836/whats-the-meaning-of-usetaskfriendlysynchronizationcontext

http://social.msdn.microsoft.com/Forums/en-NZ/async/thread/b2e8c51e-2808-46d0-92e9-b825321d0af8