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asp.net building controls : Controls not updated by callback event
We have developed a custom web control that implements ICallbackEventHandler and fires an event when the callback is invoked. We had hoped that subscribers to this event would be able to update the state of other web controls but have been unable to make this work. I have distilled the control down to the minimum required to illustrate the issue and have shown a minimal consumer web form (both are inline below). In the web form, both Button1_Click and Wrapper1_Save are called (verified through breakpoints) but the latter does not update the label properly. Is this a limitation of the modified callback lifecycle or is there some way to make it work? Thanks, Dave --- start of control --- using System; using System.Web.UI; using System.Web.UI.WebControls; namespace MyControls { [ToolboxData("<{0}:MyControl runat=\"server\"></{0}:MyControl>")] public class MyControl : WebControl, ICallbackEventHandler { public event EventHandler MyEvent; private string result; protected override void OnInit(EventArgs e) { base.OnInit(e); Page.ClientScript.RegisterClientScriptBlock(typeof(MyControl), "OnSuccess", "function OnSuccess(result, context) {}", true); string callback = Page.ClientScript.GetCallbackEventReference(this, "result", "OnSuccess", "context"); Page.ClientScript.RegisterClientScriptBlock(typeof(MyControl), ID, string.Concat("function ", ID, "Callback(result, context) { ", callback, "; }"), true); } public void RaiseCallbackEvent(string eventArgument) { result = eventArgument; if (MyEvent != null) { MyEvent(this, EventArgs.Empty); } } public string GetCallbackResult() { return result; } } } --- end of control --- --- start of web page --- <%@ Page Language="C#" %> <%@ Register TagPrefix="custom" Namespace="MyControls" %> <script runat="server"> protected void Button1_Click(object sender, EventArgs e) { Label1.Text = "PostBack button clicked"; } protected void Wrapper1_Save(object sender, EventArgs e) { Label1.Text = "CallBack button clicked"; } </script> <html> <head> <title>Test Page</title> </head> <body> <form id="form1" runat="server"> <div> <custom:MyControl ID="MyControl1" OnMyEvent="Wrapper1_Save" runat="server" /> <asp:Button ID="Button1" Text="PostBack" runat="server" OnClick="Button1_Click" /> <asp:Button ID="Button2" Text="CallBack" OnClientClick="MyControl1Callback('Testing123', null)" runat="server" /> <asp:Label ID="Label1" runat="server" /> </div> </form> </body> </html>
Hi Dave,
In a client callback, a client script function sends a request to the ASP.NET Web page, which then runs an abbreviated version of its normal life cycle to process the callback: the page is initiated and its controls and other members are created, and then a specially marked method is invoked. The method performs the processing that you have coded and then returns a value to the browser that can be read by another client script function. Besides implementing ICallbackEventHandler and its methods RaiseCallbackEvent, GetCallbackResult, the page must contain three client script functions that perform the following actions: * One function calls a helper method that performs the actual request to the server. In this function, you can perform custom logic to prepare the event arguments first, and then you can send a string as a parameter to the server-side callback event handler. * Another function receives (is called by) the result from the server code that processed the callback event, accepting a string that represents the results. This is called the client callback function. * A third function is the helper function that performs the actual request to the server, which is generated automatically by ASP.NET when you generate a reference to this function using the GetCallbackEventReference method in server code. The key point here is that it's not a postback, the page will not be rendered again; if you change the server-side controls' properties, the changes will not be rendered. Therefore, in your code, if we make following changes: (In MyControl) protected override void OnInit(EventArgs e) { base.OnInit(e); //Page.ClientScript.RegisterClientScriptBlock(typeof(MyControl), "OnSuccess", "function OnSuccess(result, context) { }", true); string callback = Page.ClientScript.GetCallbackEventReference(this, "result", string.Concat(ID, "OnSuccess"), "context"); Page.ClientScript.RegisterClientScriptBlock(typeof(MyControl), ID, string.Concat("function ", ID, "Callback(result, context) { ", callback, "; }"), true); } (In ASPX) <head> <title>Test Page</title> <script language="javascript" type="text/javascript"> function MyControl1OnSuccess(text) { alert(text); } </script> </head> References: #Implementing Client Callbacks Without Postbacks in ASP.NET Web Pages http://msdn2.microsoft.com/en-us/library/ms178208.aspx #Client-Callback Implementation (C#) Example http://msdn2.microsoft.com/en-us/library/ms178210.aspx Sincerely, Walter Wang (wawang@online.microsoft.com, remove 'online.') Microsoft Online Community Support ================================================== For MSDN subscribers whose posts are left unanswered, please check this document: http://blogs.msdn.com/msdnts/pages/postingAlias.aspx Get notification to my posts through email? Please refer to http://msdn.microsoft.com/subscriptions/managednewsgroups/default.aspx#notif ications. If you are using Outlook Express/Windows Mail, please make sure you clear the check box "Tools/Options/Read: Get 300 headers at a time" to see your reply promptly. Note: The MSDN Managed Newsgroup support offering is for non-urgent issues where an initial response from the community or a Microsoft Support Engineer within 1 business day is acceptable. Please note that each follow up response may take approximately 2 business days as the support professional working with you may need further investigation to reach the most efficient resolution. The offering is not appropriate for situations that require urgent, real-time or phone-based interactions or complex project analysis and dump analysis issues. Issues of this nature are best handled working with a dedicated Microsoft Support Engineer by contacting Microsoft Customer Support Services (CSS) at http://msdn.microsoft.com/subscriptions/support/default.aspx. ================================================== This posting is provided "AS IS" with no warranties, and confers no rights.
Hi Dave,
Some updates: <html> <head> <title>Test Page</title> <script language="javascript" type="text/javascript"> function MyControl1OnSuccess(text) { //alert(text); document.getElementById("Label1").innerHTML = text; } </script> </head> <body> <form id="form1" runat="server"> <div> <custom:MyControl ID="MyControl1" OnMyEvent="Wrapper1_Save" runat="server" /> <asp:Button ID="Button1" Text="PostBack" runat="server" OnClick="Button1_Click" /> <asp:Button ID="Button2" Text="CallBack" OnClientClick="MyControl1Callback('Testing123', null); return false;" runat="server" /> <asp:Label ID="Label1" runat="server" /> </div> </form> </body> </html> 1) To update the label's content on callback, use DHTML dom elements to change its content. 2) You need to add "return false" in button2's OnClientClick, otherwise there's an additional normal postback at the end (which will re-render the page content according to server-side controls' states -- which means the label1's content that we changed via script callback will be overwritten again). Hope this helps. Regards, Walter Wang (wawang@online.microsoft.com, remove 'online.') Microsoft Online Community Support ================================================== When responding to posts, please "Reply to Group" via your newsreader so that others may learn and benefit from your issue. ================================================== This posting is provided "AS IS" with no warranties, and confers no rights.
Hey Walter,
Thanks for that very good explanation. We are in fact trying to wrap some AJAX type behaviour in a control and wanted to insulate the consumer of the wrapper from having to code any javascript. Looks like that is not possible so we'll be using something similar to what you have suggested. Thanks again! Dave [quoted text, click to view] ""Walter Wang [MSFT]"" wrote:
> Hi Dave, > > Some updates: > > <html> > <head> > <title>Test Page</title> > > <script language="javascript" type="text/javascript"> > function MyControl1OnSuccess(text) { > //alert(text); > document.getElementById("Label1").innerHTML = text; > } > </script> > </head> > <body> > <form id="form1" runat="server"> > <div> > <custom:MyControl ID="MyControl1" OnMyEvent="Wrapper1_Save" > runat="server" /> > <asp:Button ID="Button1" Text="PostBack" runat="server" > OnClick="Button1_Click" /> > <asp:Button ID="Button2" Text="CallBack" > OnClientClick="MyControl1Callback('Testing123', null); return false;" > runat="server" /> > <asp:Label ID="Label1" runat="server" /> > </div> > </form> > </body> > </html> > > > 1) To update the label's content on callback, use DHTML dom elements to > change its content. > > 2) You need to add "return false" in button2's OnClientClick, otherwise > there's an additional normal postback at the end (which will re-render the > page content according to server-side controls' states -- which means the > label1's content that we changed via script callback will be overwritten > again). > > > Hope this helps. > > > Regards, > Walter Wang (wawang@online.microsoft.com, remove 'online.') > Microsoft Online Community Support > > ================================================== > When responding to posts, please "Reply to Group" via your newsreader so > that others may learn and benefit from your issue. > ================================================== > > This posting is provided "AS IS" with no warranties, and confers no rights. >
Hi Dave,
I'm glad that the reply helped. Thank you for using MSDN Managed Newsgroup support service! Regards, Walter Wang (wawang@online.microsoft.com, remove 'online.') Microsoft Online Community Support ================================================== When responding to posts, please "Reply to Group" via your newsreader so that others may learn and benefit from your issue. ================================================== This posting is provided "AS IS" with no warranties, and confers no rights.
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