//this event fire when user don't focus on it
 private void txtname_Validated(object sender, EventArgs e)
 {
     BL.Product product = new BL.Product();
     if (product.Check_Product_Name(txtname.Text)) { MessageBox.Show("هذا المنتج موجود بالفعل", "تنبيه", MessageBoxButtons.OK, MessageBoxIcon.Warning);
     txtname.Focus();
     txtname.SelectionStart = 0;
     txtname.SelectionLength = txtname.TextLength;
     }
 }