private void addToolStripMenuItem_Click(object sender, EventArgs e)
 {
     addForm = new BookAddForm(null);
     if (addForm.ShowDialog() == DialogResult.OK)
     {
         Book book = new Book(addForm.BookTitle(), addForm.BookAuthor(), addForm.BookDate(), addForm.BookCategory());
         items.Add(book);
         ListViewItem item = new ListViewItem();
         item.Tag = book;
         UpdateItem(item);
         mainForm.addBookInAllViews(book);
     }
 }
        private void editToolStripMenuItem_Click(object sender, EventArgs e)
        {
            if (listView1.SelectedItems.Count == 1)
            {
                Book book = (Book)listView1.SelectedItems[0].Tag;
                addForm = new BookAddForm(book);

                if (addForm.ShowDialog() == DialogResult.OK)
                {
                    book.title    = addForm.BookTitle();
                    book.author   = addForm.BookAuthor();
                    book.date     = addForm.BookDate();
                    book.category = addForm.BookCategory();

                    UpdateItem(listView1.SelectedItems[0]);
                    mainForm.updateBookInAllViews(book);
                }
            }
        }