Since it is hard to determine that the RadGrid1 button column has triggered the AJAX request, you need to attach a click handler to all buttons from the column on the server and use an additional flag:
<%@ Page Language="C#" %>
<%@ Import Namespace="System.Data" %>
<%@ Register Assembly="Telerik.Web.UI" Namespace="Telerik.Web.UI" TagPrefix="telerik" %>
<script runat="server">
protected void RadGrid_NeedDataSource(object sender, GridNeedDataSourceEventArgs e)
{
DataTable dt = new DataTable();
DataRow dr;
int colsNum = 4;
int rowsNum = 15;
string colName = "Column";
for (int j = 1; j <= colsNum; j++)
{
dt.Columns.Add(String.Format("{0}{1}", colName, j));
}
for (int i = 1; i <= rowsNum; i++)
{
dr = dt.NewRow();
for (int k = 1; k <= colsNum; k++)
{
dr[String.Format("{0}{1}", colName, k)] = String.Format("{0}{1} Row{2}", colName, k, i);
}
dt.Rows.Add(dr);
}
(sender as RadGrid).DataSource = dt;
}
protected void RadGrid1_ItemCreated(object sender, GridItemEventArgs e)
{
if (e.Item is GridDataItem)
{
((e.Item as GridDataItem)["gbcAdd"].Controls[0] as Button).OnClientClick = "isRadGrid1ButtonPressed = true;";
}
}
</script>
<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN"
<head id="Head1" runat="server">
<meta http-equiv="content-type" content="text/html;charset=utf-8" />
<title>RadControls</title>
</head>
<body>
<form id="form1" runat="server">
<asp:ScriptManager ID="ScriptManager1" runat="server" />
<telerik:RadAjaxLoadingPanel ID="RadAjaxLoadingPanel1" runat="server" Skin="Vista" OnClientShowing="MyClientShowing" />
<telerik:RadAjaxManager ID="RadAjaxManager1" runat="server" DefaultLoadingPanelID="RadAjaxLoadingPanel1">
<ClientEvents OnRequestStart="MyRequestStart" />
<AjaxSettings>
<telerik:AjaxSetting AjaxControlID="RadGrid1">
<UpdatedControls>
<telerik:AjaxUpdatedControl ControlID="RadGrid1" />
<telerik:AjaxUpdatedControl ControlID="RadGrid2" />
</UpdatedControls>
</telerik:AjaxSetting>
<telerik:AjaxSetting AjaxControlID="RadGrid2">
<UpdatedControls>
<telerik:AjaxUpdatedControl ControlID="RadGrid2" />
</UpdatedControls>
</telerik:AjaxSetting>
</AjaxSettings>
</telerik:RadAjaxManager>
<script type="text/javascript">
var isRadGrid1Initiator = false;
var isRadGrid1ButtonPressed = false;
function MyRequestStart(sender, args)
{
if (!isRadGrid1ButtonPressed && args.get_eventArgument().indexOf("RowDropped") == -1 && args.get_eventTarget().indexOf("RadGrid1") != -1)
isRadGrid1Initiator = true;
}
function MyClientShowing(sender, args)
{
if (isRadGrid1Initiator && args.get_updatedElement().id.indexOf("RadGrid2") != -1)
{
args.set_cancelNativeDisplay(true);
isRadGrid1Initiator = false;
}
isRadGrid1ButtonPressed = false;
}
</script>
<telerik:RadGrid
ID="RadGrid1"
runat="server"
Skin="Vista"
AllowPaging="true"
OnNeedDataSource="RadGrid_NeedDataSource" OnItemCreated="RadGrid1_ItemCreated">
<ClientSettings AllowRowsDragDrop="true">
<Selecting AllowRowSelect="true" />
</ClientSettings>
<MasterTableView>
<Columns>
<telerik:GridButtonColumn UniqueName="gbcAdd" Text=" " HeaderText="Add"
ButtonType="PushButton" ButtonCssClass="rgAdd" Visible="true" CommandName="AddUser">
</telerik:GridButtonColumn>
</Columns>
</MasterTableView>
</telerik:RadGrid>
<br /><br />
<telerik:RadGrid
ID="RadGrid2"
runat="server"
Skin="Vista"
AllowPaging="true"
OnNeedDataSource="RadGrid_NeedDataSource">
</telerik:RadGrid>
</form>
</body>
</html>