default.aspx
<asp:GridView ID="GridView1" runat="server" AutoGenerateColumns="False" OnSelectedIndexChanged="GridView1_SelectedIndexChanged">
<Columns>
<asp:BoundField HeaderText="col1">
<ItemStyle Width="200px" />
</asp:BoundField>
<asp:BoundField HeaderText="col2">
<ItemStyle Width="50px" />
</asp:BoundField>
<asp:CommandField SelectText="Reply" ShowSelectButton="True" />
</Columns>
</asp:GridView>
default.aspx.cs
protected void Page_Load(object sender, EventArgs e)
{
if (!IsPostBack)
{
panel1.visible = false;
}
}
protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
panel1.visible=true;
}