How to Disable Textbox in Gridview If the Texbox is not null

       gvDetails.EditIndex = e.NewEditIndex;
        BindEmployeeDetails();
        TextBox txt_FName = (TextBox)gvDetails.Rows[e.NewEditIndex].FindControl("txt_FName");
        txt_FName.Visible = false;

hi,
try like this. it may work.


  protected void GridView1_RowEditing(object sender, GridViewEditEventArgs e)
{
gvAssginingView.EditIndex = e.NewEditIndex;
gridbind();
TextBox TxtVal = (TextBox)gvAssginingView.Rows[e.NewEditIndex].FindControl("txtDriverCode");
if (TxtVal.Text != string.Empty)
{
    TxtVal.Enabled = false;
}
else
{
    TxtVal.Enabled = true;
}
}

please check below link-: 

http://onetidbit.wordpress.com/2009/05/04/disabling-some-of-the-textboxes-in-gridview-edit/

similiar to what you did..

hope this helps !!