private void btnAdd_Click(object sender, EventArgs e)
 {
     using (frmAddEditBook frm = new frmAddEditBook(null))
     {
         if (frm.ShowDialog() == DialogResult.OK)
         {
             bookBindingSource.DataSource = _controller.GetAll();
         }
     }
 }
        private void btnEdit_Click(object sender, EventArgs e)
        {
            if (bookBindingSource.Current == null)
            {
                return;
            }

            using (frmAddEditBook frm = new frmAddEditBook(bookBindingSource.Current as Book))
            {
                if (frm.ShowDialog() == DialogResult.OK)
                {
                    bookBindingSource.DataSource = _controller.GetAll();
                }
            }
        }