从AJAX和C＃加载UI控件

Question

I am trying to dynamically load a PlaceHolder with a *.ascx page from a AJAX call. But am running into an issue with the static aspect.

I cannot access the PlaceHolder as it's not a static member. My code is as follows:

HTML:

    <div id="DInfo">
        <asp:PlaceHolder ID="PlaceHolderDInfo" runat="server"></asp:PlaceHolder>  
        <div id="response"></div>  
    </div>

C#:

    [WebMethod]
    public static void SetD()
    {
       //SOME LOGIC TO FIND CORRECT ASCX PAGE
       ...

       //Load the control 
       PlaceHolderDInfo.Controls.Add(LoadControl([path to ascx]));
    }

AJAX:

    $.ajax({
      type: "POST",
      url: "LivePlayer.aspx/SetD",
      contentType: "application/json; charset=utf-8",
      dataType: "json",
      success: function (response) {
        $("#response").html(response.d);
      },
      failure: function (response) {
         $("#response").html("error");
    }

The problem happens in the C# section as "PlaceHolderDInfo" throws the error:

• " An object reference is required for the non-static field, method, or property ..."

How can I reach the PlaceHolder from the SetD() method?

Thanks for any advice!

Answer 1

Your code in the web method cannot use any object in your ASP.NET page. Reason being: it's operating separately from the ASP.NET page process, therefore it knows nothing about viewstate, etc. You should treat it like any other web service.

That said, what needs to return is a string; please note, ASP.NET web forms and dynamic controls this way is not as easy as a framework like ASP.NET MVC, so you will have to overcome technical hurdles to get it to work. First being: any controls added by returning HTML as string and adding it to the DOM will not be retained in the postback lifecycle, and there will be issues with viewstate.

It is possible to return a user control as a string; I've seen it setup as a handler, which streams back HTML as a string, but can't find the setup I've seen before.