How do I do a client callback using vbscript? 1

[FancyPrairie]

I'm using ASP.Net 2.0 and am trying to figure out how to perform client callbacks. I've seen complicated examples using javascript but none using vbscript. Does anyone know how to do it in vbscript?

For an example, I would like to call a server-side class function from a html page. All the server-side class function needs to do is to return the current system time and date as a string.

Any help?

 

[tgreer]

You cannot, strictly speaking.

You can use AJAX to generate a second, "hidden" request via the XMLHTTPRequest object. Sorry, I don't have a VBScript example.

The web doesn't support "client callbacks", only HTTP Get and Post, period.







Thomas D. Greer

http://www.tgreer.com

 

[FancyPrairie]

Are you saying it can't be done with vbscript or it can't be done period?

 

[checkai]

I'm doing callbacks with 2.0 but with Javascript...seems that you'd just need to format your script correctly...let me know if you want me to post my code...as I struggled with examples that I found on the web as well..

"...we both know I'm training to become a cagefighter...see what happens if you try 'n hit me..."

 

[jbenson001]

checkai.. I would like to see your code since the examples I have found are complicated.

Thanks,

Jim

 

[FancyPrairie]

checkai, I would appreciate a simple example of how it works (like the example I explained in my first post). I'm sure you're busy and understand if you can't get to it.

 

[checkai]

here's my javascript code

<script language="javascript" type="text/javascript">   
function ClientCallback(result, context){
 var DropDown = document.forms[0].elements['<%=listbox.UniqueID%>'];

 if (!DropDown){
  return;
 }

 DropDown.length = 0;
 if (!result){
  return;
 }
      
 var rows = result.split('|'); 
 for (var i = 0; i < rows.length; ++i){
  var shz = rows[i].split('^');
  var option = document.createElement("OPTION");
  option.value = shz[0];
  option.innerHTML = shz[1];
  DropDown.appendChild(option);
 }
 DropDown.selectedIndex=0;
}

function ClientCallbackError(result, context){
 alert(result);
}
</script>

<asp:TextBox ID="txtSearch" runat="server" onkeyup="Search(this.value + '%', 'ddl');" EnableViewState="False"> </asp:TextBox>

vb code

Partial Class wfrmHome
 Inherits System.Web.UI.Page
 Implements ICallbackEventHandler
 Private callbackresult As String

 Private Sub Page_Load(ByVal source As Object, ByVal e As System.EventArgs)
  Dim callBack As String = Page.ClientScript.GetCallbackEventReference(Me, "arg", "ClientCallback", "context", "ClientCallbackError", False)
  Dim clientFunction As String = "function Search(arg, context){ " & callBack & "; }"
  Page.ClientScript.RegisterClientScriptBlock(Me.GetType(), "Search", clientFunction, True)
 End Sub

 Public Function GetCallbackResult() As String Implements System.Web.UI.ICallbackEventHandler.GetCallbackResult
  Return callbackresult
 End Function

 Public Sub RaiseCallbackEvent(ByVal eventArgument As String) Implements System.Web.UI.ICallbackEventHandler.RaiseCallbackEvent
  Dim a As MyData = New MyData
  Dim dt As Data.DataTable = a.searchClient(eventArgument, "dc9974")

  If dt.Rows.Count > 50 Then
    callbackresult = "0^...searching..."
  ElseIf dt.Rows.Count = 0 Then
    callbackresult = "0^...no clients found..."
  Else
    Dim str As String = ""
    Dim i As Integer = 0
    Do While i < dt.Rows.Count
     str += dt.Rows(i)("clientID") & "^" & dt.Rows(i)("clientName") & "|"
     i += 1
    Loop
    callbackresult = str.Remove(str.LastIndexOf("|"), 1)
  End If

  dt.Dispose()
  dt = Nothing
  a.Dispose()
  a = Nothing
End Sub

  Protected Sub btnSelect_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnSelect.Click
    Dim cID As Integer = CInt(Request.Form("listbox"))
  End Sub
End Class

this code basically does a client search as you type in the text box...

"...we both know I'm training to become a cagefighter...see what happens if you try 'n hit me..."

 

[jbenson001]

great example.. thanks

 

[FancyPrairie]

Ok, I'm stupid. I can't get the example to run (note this is my first asp.net app...so what do I need to do to make it work?

 

[checkai]

you'll need to change a few things...for instance this code is calling a search class that i have...

Dim a As MyData = New MyData
Dim dt As Data.DataTable = a.searchClient(eventArgument, "dc9974")

"...we both know I'm training to become a cagefighter...see what happens if you try 'n hit me..."

 

[tgreer]

But you can see from that code that a true "callback" isn't being done. The textbox is coded to run on the server, and the server code runs each time a key is released. You can call it a "callback" if you wish, but it's really just an HTTP Post.

Nevermind, it's just semantics I suppose.

Thomas D. Greer

http://www.tgreer.com

 

[checkai]

Semantics that I don't understand!! but I believe Asp.Net 2 advertises it as "Client Callback" don't they?

"...we both know I'm training to become a cagefighter...see what happens if you try 'n hit me..."

 

[ca8msm]

There is a MSDN article on client callbacks with an example walkthrough if anyone is having problems understanding them:

http://msdn2.microsoft.com/en-us/library/ms178208.aspx

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[FancyPrairie]

checkai, I think the reason I couldn't get your example to work is because I have the beta version of 2.0. It's missing some things.

ca8msm, the link looks promising. I will check it out after the New Year.

 

[tgreer]

Hmm. I see the teriminology, yes, but the only way for a page to send a "request" to a server is via HTTP Get/Post or the XmlHttpRequest object. To keep the page "live in the client browser" while sending and a processing a separate request is known in the web development community as "AJAX".

It appears ASP.NET exploits this but is calling it "Client Callbacks" instead. All well and good, I suppose.



Thomas D. Greer

http://www.tgreer.com