GridView Filter using DropDownlist

protected void DropDownList14324235_TextChanged(object sender, EventArgs e)
   {

       DropDownList t = (DropDownList)sender;
       var sbFilter = new System.Text.StringBuilder();


       if (t.SelectedValue.Length > 0)
       {

           sbFilter.Append("Group_Id ='" + t.SelectedValue + "'");

           ObjectDataSource1.FilterExpression = sbFilter.ToString();
       }
       else
       {
           ObjectDataSource1.FilterExpression = string.Empty;
           ObjectDataSource1.FilterParameters.Clear();

       }
   }