Hi Tbaseflug,
Here's a sample which I think demonstrates the scenario.
Example (Parent)
<%@ Page Language="C#" %>
<%@ Register Assembly="Coolite.Ext.Web" Namespace="Coolite.Ext.Web" TagPrefix="ext" %>
<!DOCTYPE html PUBLIC "-W3CDTD XHTML 1.0 TransitionalEN"
"http:www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html>
<head id="Head1" runat="server">
<title></title>
</head>
<body>
<form id="form1" runat="server">
<ext:ScriptManager ID="ScriptManager1" runat="server" />
<ext:Window
ID="Window1"
runat="server"
Title="Parent"
Width="300"
Height="185">
<Body>
<ext:FitLayout runat="server">
<ext:TabPanel
ID="TabPanel1"
runat="server"
ActiveTabIndex="0"
Height="300"
Border="false">
<Defaults>
<ext:Parameter Name="bodyStyle" Value="padding:6px;" />
</Defaults>
<Tabs>
<ext:Tab ID="Tab1" runat="server" Title="Tab 1">
<Body>
<ext:FormLayout runat="server">
<Anchors>
<ext:Anchor Horizontal="100%">
<ext:ComboBox
ID="ComboBox1"
runat="server"
FieldLabel="Options"
Editable="false">
<SelectedItem Value="1" />
<Items>
<ext:ListItem Text="Item 1" Value="1" />
<ext:ListItem Text="Item 2" Value="2" />
<ext:ListItem Text="Item 3" Value="3" />
<ext:ListItem Text="Item 4" Value="4" />
</Items>
</ext:ComboBox>
</ext:Anchor>
</Anchors>
</ext:FormLayout>
</Body>
</ext:Tab>
<ext:Tab ID="Tab2" runat="server" Title="Tab 2">
<AutoLoad Url="Child.aspx" Mode="IFrame" ShowMask="true" />
<Listeners>
<Activate Handler="el.autoLoad.params = { item: ComboBox1.getValue() }; el.reload();" />
<Deactivate Handler="el.clearContent();" />
</Listeners>
</ext:Tab>
</Tabs>
</ext:TabPanel>
</ext:FitLayout>
</Body>
</ext:Window>
</form>
</body>
</html>
Example (Child)
<%@ Page Language="C#" %>
<%@ Register Assembly="Coolite.Ext.Web" Namespace="Coolite.Ext.Web" TagPrefix="ext" %>
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
System.Threading.Thread.Sleep(500);
this.Label1.Text = string.Concat("You choose Item #", Request.QueryString["item"]);
}
</script>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
"http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">
<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
<title>Child Window</title>
</head>
<body>
<ext:ScriptManager runat="server" />
<ext:Label ID="Label1" runat="server" />
</body>
</html>
The only tricky part was figuring out how to pass the ComboBox1 selected value to the params object. Typically this would be handled by configuring the inner <Params> property, but there was a problem. Adding the following bit to the <Active> Handler was the solution.
Example
el.autoLoad.params = { item: ComboBox1.getValue() };
Hope this helps.