data not shown in GridView1

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C#

ASP.NET

I have written this html code in aspx page--

<td align="center">
<asp:LinkButton ID="viewdata" runat="server" onclick="viewdata_Click">
    viewdata</asp:LinkButton>
    <br />
    <asp:GridView ID="GridView1" runat="server">
    </asp:GridView>
</td>

And i have written this code in my cs page::--

protected void viewdata_Click(object sender, EventArgs e)//Code to View 

        //// the data from the SQL Server
    {
        SqlConnection conn = new SqlConnection("user id=sa;" +
                                       "password=prodip@km;server=PRODIP;" +
                                       "Trusted_Connection=yes;" +
                                       "database=Member;");
        try
        {
            SqlDataAdapter sda = new SqlDataAdapter("select * from emp", conn);
            DataSet ds = new DataSet();
            sda.Fill(ds);
            GridView1.DataSource = ds;
            GridView1.DataBind();

        }
}

But the problem is ==the following two line shown as red underline & show the mess that
GridView1 dose not exit in current context..
the line are--

GridView1.DataSource = ds;
GridView1.DataBind();


please help me where is my mistake..