How to call text changed event of textbox in gridview.

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C#

ASP.NET

Hello, I am lakshmana rao.
my web page having an gridview just as below

<pre lang="c#"> <asp:GridView ID="GridView2" runat="server" ShowFooter="True" CssClass="grid"
                AutoGenerateColumns="False" 
                 onrowcreated="GridView2_RowCreated" CellPadding="4" ForeColor="#333333" 
                 GridLines="None" Width="100%">
                  <AlternatingRowStyle BackColor="White" />
            <Columns>
                <asp:BoundField HeaderText="S.NO" DataField="s.NO" />                     
                <asp:TemplateField HeaderText="Task">
               <ItemTemplate>
                   <asp:TextBox ID="TextBox2" runat="server" OnTextChanged=TextBox2_textchanged" CssClass="gridtextbox">
</asp:TextBox>
</Columns>   
 </asp:GridView>

and i want to write event of "text_changed".
and write code behind code as follows...

<pre lang="c#">
protected void TextBox4_leave(object sender, EventArgs e)
{

}

but this event is not fired when the text changed.
so please find me the solution...