protected void GridView1_RowDataBound(object sender, GridViewRowEventArgs e)
{

foreach(GridViewRow row in GridView1.rows)
{

TextBox tb = (TextBox) row.Cells[1].FindControl("TextBox1") ;
TextBox tb1 = (TextBox) row.FindControl("TextBox1") ;

if ( tb = null || tb1 != null)
{
     Response.write( TextBox tb = (TextBox) row.Cells[1].FindControl("TextBox1").Text );
}
}

and it's still null