Gridview Filter

[Parthiv]

hello
i am face one problem regarding gridview filter
in my gridview columns are dynamically added from code behind 

<grid:RadGridView x:Name="FormsGrid"
    Margin="5,0,10,0"
    CanUserFreezeColumns="False"
    AutoGenerateColumns="False"
    ScrollMode="RealTime"
    MinHeight="300"
    BorderThickness="1,6,1,1"
    telerik:StyleManager.Theme="Office_Blue"
    ScrollViewer.HorizontalScrollBarVisibility="Visible"
    ItemsSource="{Binding PagedSource, ElementName=radDataPager1}"
    ScrollViewer.VerticalScrollBarVisibility="Auto"
    SelectionChanged="FormsGrid_SelectionChanged"
    DataLoaded="FormsGrid_DataLoaded"
    LayoutUpdated="FormsGrid_LayoutUpdated"
    CanUserDeleteRows="False"
    CanUserInsertRows="False"
    IsFilteringAllowed="True">
</grid:RadGridView>

  Code Behind file

FormsGrid.Columns.Clear();
FormsGrid.AutoGenerateColumns = false;
for (int i = 0; i < columnCount; i++)
{
    XElement element = myDoc.Element("NewDataSet").Element("Table").Elements().ElementAt(i);

    dgtc = new GridViewDataColumn();
    dgtc.MinWidth = 100;
    dgtc.IsReadOnly = true;
    dgtc.Width = GridViewLength.SizeToHeader;

    dgtc.Header = element.Name.ToString().Replace("_x0020_", " ").Replace("_x0028_", " (").Replace("_x0029_", ") ");

    dgtc.DataMemberBinding = new Binding(element.Name.ToString().Replace("-", " "));
    dgtc.DataMemberBinding.Source = element.Name;

    indexingConverter convert = new indexingConverter();
    Binding bind = new Binding { Converter = convert, ConverterParameter = element.Name };

    dgtc.DataMemberBinding = bind;
    dgtc.IsFilterable = true;
    FormsGrid.Columns.Add(dgtc);
}

in code i am set a column's IsFilterable = true
but filter icon not shown in gridview