如何在ASP.net WebForms的服务器端使用async / await预渲染UserControl

Question

I have to deal with a WebForms (.Net 4.7) application, that loads server-side prerendered UserControls, by calling a HttpHandler by Javascript/Angular from client-side.

The HttpHandler prerenders the UserControls by this old "hack"

public class MyHandler : IHttpHandler
{
    public override void ProcessRequest(HttpContext context)
    {
        var page = new Page();
        var control = page.LoadControl("~/MyFancyUC.ascx");
        var form = new HtmlForm { ID = "Form1" };               
        form.Controls.Add(control);         
        page.Controls.Add(form);
        var stringBuilder = new StringBuilder();

        using (StringWriter output = new StringWriter(stringBuilder))
        {
            HttpContext.Current.Server.Execute(page, output, false);
        }

        context.Response.Write(stringBuilder.ToString());
    }
}

As this style worked several years very well, I can't use async/await style within the UserControls, because I'm getting an error, that the Page needs to have the Async=true attribute.

The UserControls look like this:

public partial class MyFancyUC: UserControl
{       

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

    private async Task HandleAsync()
    {
        var data = await GetDataAsync();
        BindData(data);
    }
}

I already tried to create a simple page class, that sets the Async mode programmatically, and use it in the "MyHandler" HttpHandler, but this doesn't work either.

public class AsyncPage : Page
{
    public AsyncPage()
    {
        this.AsyncMode = true;
    }       
}

}

When I debug the UserControl, the Page property always shows AsyncMode=false, IsAsync = false.

So I guess, this is caused by HttpServerUtility.Execute() call, that is not capable of running a WebForms page in Async mode.

Does anyone know how to deal with this ?

Answer 1

An asynchronous HTTP handler must implement IHttpAsyncHandler Interface .

An asynchronous Page must have its AsyncMode property set to true .

Answer 2

您必须使用IHttpAsyncHandler