private void txtBarCode_Leave(object sender, EventArgs e)
{
if (this.txtBarCode.Text.Trim().Length > 0)
{
if (objBookManager.BarCodeExistsed(this.txtBarCode.Text.Trim()))
{
MessageBox.Show("this book exists in database");
this.txtBarCode.SelectAll();
this.txtBarCode.Focus();
}
}
}