I would implement it this way.
Example
<%@ Page Language="C#" %>
<%@ Register Assembly="Ext.Net" Namespace="Ext.Net" TagPrefix="ext" %>
<script runat="server">
protected void Page_Load(object sender, EventArgs e)
{
if (!X.IsAjaxRequest)
{
this.Store1.DataSource = new object[]
{
new object[] { "test1", "test2", "test3" },
new object[] { "test4", "test5", "test6" },
new object[] { "test7", "test8", "test9" },
};
this.Store1.DataBind();
}
}
</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>Ext.Net Example</title>
<script type="text/javascript">
var showMask = function (grid, dataIndex) {
var colModel = grid.getColumnModel(),
colIndex = colModel.findColumnIndex(dataIndex);
colModel.setRenderer(colIndex, maskRenderer);
grid.getView().refresh();
};
var hideMask = function (grid, dataIndex) {
var colModel = grid.getColumnModel(),
colIndex = colModel.findColumnIndex(dataIndex);
colModel.setRenderer(colIndex, function (value) { return value; });
grid.getView().refresh();
};
var maskRenderer = function (value, metaData, record, rowIndex, colIndex, store) {
metaData.css = "mask-column";
return value;
};
</script>
<style type="text/css">
.mask-column {
back: gray;
}
</style>
</head>
<body>
<form runat="server">
<ext:ResourceManager runat="server" />
<ext:GridPanel ID="GridPanel1" runat="server" AutoHeight="true">
<Store>
<ext:Store ID="Store1" runat="server">
<Reader>
<ext:ArrayReader>
<Fields>
<ext:RecordField Name="test1" />
<ext:RecordField Name="test2" />
<ext:RecordField Name="test3" />
</Fields>
</ext:ArrayReader>
</Reader>
</ext:Store>
</Store>
<ColumnModel runat="server">
<Columns>
<ext:Column Header="Test1" DataIndex="test1" />
<ext:Column Header="Test2" DataIndex="test2" />
<ext:Column Header="Test3" DataIndex="test3" />
</Columns>
</ColumnModel>
</ext:GridPanel>
<ext:Button runat="server" Text="Show mask">
<Listeners>
<Click Handler="showMask(GridPanel1, 'test2')" />
</Listeners>
</ext:Button>
<ext:Button runat="server" Text="Hide mask">
<Listeners>
<Click Handler="hideMask(GridPanel1, 'test2')" />
</Listeners>
</ext:Button>
</form>
</body>
</html>