ASP.NET -> Synchronous call to a javascript function

Question

I'm in need of a synchronous call from code-behind ASP.NET (C#) to a Javascript function.

I've tried the ScriptManager.Registerclient, but as this is asynchronous this is no good. I'm in need of some testing in javascript before returning a value (updating an UpdatePanel) to check whether or not the operation is valid.

For a short code example:

myButton_click(object sender, EventArgs args)
{
  <callJavascriptSynchronous>
  if (MyHiddenField.Value == "true")
     //Do
else
   //Don't
}

MyHiddenField is within an UpdatePanel. For the javascript function:

function javascriptFoo(myInteger)
{
  var returnValue = window.external.TestInteger(myInteger);
  document.getElementById('<%=MyHiddenField.ClientID%>').value = returnValue;
}

The UpdatePanel looks like this:

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
    <asp:HiddenField ID="MyHiddenField" runat="server" ClientIDMode="Static" Value="" Visible="false"/>
</ContentTemplate>

Any suggestions on the synchronous call?

Thanks!

Edit: Added full code:

MyPage.aspx:

function javascriptFoo(myInteger)
{
  var returnValue = window.external.TestInteger(myInteger);
  document.getElementById('<%=MyHiddenField.ClientID%>').value = returnValue;
}

<asp:UpdatePanel ID="UpdatePanel1" runat="server">
<ContentTemplate>
    <asp:HiddenField ID="MyHiddenField" runat="server" ClientIDMode="Static" Value="" Visible="false"/>
</ContentTemplate>

<asp:GridView ID="GridView1" runat="server" OnRowCommand="GridView1_RowCommand">

MyPage.aspx.cs:

protected void GridView1_RowCommand(object sender, GridViewCommandEventArgs e)
{
   ScriptManager.RegisterStartupScript(UpdatePanelContext, UpdatePanelContext.GetType(), "AlertTest", "AlertTest()", true);

   string sVal = HiddenFieldContext.Value;

   if (sVal == "true") //do
   else //don't
}

Alexander · Accepted Answer · 2014-09-04 08:33:53Z

1

When you're in your button's click-event, you've already left the frontend and cannot jump back for a function call. Execute the function first, clientside, upon the button-click (read about the OnClientClick event), then return your result with the postback.

This link addresses the same issue.

edited Sep 4, 2014 at 8:33

answered Sep 4, 2014 at 7:58

Alexander

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11 Comments

user1782815 Over a year ago

Postback will do me no good, as this is happening within an operation. I'm actually doing this within a GridView.RowCommand event.

Alexander Over a year ago

Where is myButton_click?

user1782815 Over a year ago

Where it is? <asp:GridView ID="GridView1" OnRowCommand="GridView1_RowCommand"> I'm in need of testing the data within the Gridview_rowCommand event. I am able to do this, and it works, but the call is not synchronous.

Alexander Over a year ago

Is myButton_click in your frontend JavaScript or in your backend C#?

Alexander Over a year ago

It does not call a JavaScript function asynchronous. It puts the JavaScript into the page, which is then executed after the postback. You think you are executing JavaScript and you are exepcting results from it before it even reaches the client. That won't work at all. You cannot call frontend JavaScript while you are in the backend.

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