The event is not being called in ASP.NET gridview

protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
       {
           if (GridView1.SelectedRow != null)
           {
               // Retrieve the data from the selected row
               int id =
               Convert.ToInt32(GridView1.SelectedRow.Cells[0].Text);
               string selectedData = GridView1.SelectedRow.Cells[1].Text;

               // Store the id in the hidden field
               SelectedIdHiddenField.Value = id.ToString();

               // Display the selected data in the TextBox
               TextBox1.Text = selectedData;
           }
       }

 <asp:GridView ID="GridView1" 
runat="server" AutoGenerateColumns="false" 
CssClass="custom-grid fixed-header" 
OnSelectedIndexChanged="GridView1_SelectedIndexChanged" AutoPostBack="true">
                <Columns>
                     <asp:BoundField DataField="Id" 
                     HeaderText="Id"  SortExpression="Id" />
                    <%--<asp:BoundField DataField="Sr_No" 
                    HeaderText="Sr_No" ItemStyle-Width="100px" ItemStyle- 
                    HorizontalAlign="Center" 
                    HeaderStyle-HorizontalAlign="Center" />--%>
                    <asp:BoundField DataField="hobbies" 
                    HeaderText="Hobbies"  ItemStyle-Width="1100px" 
                    ItemStyle-HorizontalAlign="Left" 
                    HeaderStyle-HorizontalAlign="Left" 
                    SortExpression="hobbies" />
                </Columns>
            </asp:GridView>