Question

I’ve got this code that uses winforms to get data passed between two forms (LibraryBookDialog.cs and MainForm.cs).

Here is the code for LibraryBookDialog.cs:

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;

namespace COMP2614HomeLab08
{
    public partial class LibraryBookDialog : Form
    {
        private LibraryBook book;

        public LibraryBook Book
        {
            get
            {
                if (book == null)
                {
                    book = new LibraryBook();
                }
                return book;
            }
            set { book = value; }
        }

        public LibraryBookDialog()
        {
            InitializeComponent();
        }

        private bool validateData()
        {
            // code that validates user input data
        }

        private void buttonOk_Click(object sender, EventArgs e)
        {
            if (validateData())
            {
                try
                {
                    LibraryBook book = new LibraryBook();
                    book.Title = textBoxTitle.Text; 
                    book.Author = textBoxAuthor.Text;
                    book.CopyrightYear = Convert.ToInt32(textBoxCopyrightYear.Text);
                    this.DialogResult = DialogResult.OK;
                }
                catch (Exception ex)
                {
                    MessageBox.Show(ex.Message, "There was an error", MessageBoxButtons.OK, MessageBoxIcon.Error);
                }
            }
        }
    }
}

Here is the code for MainForm.cs:

namespace COMP2614HomeLab08
{
    public partial class MainForm : Form
    {
        public MainForm()
        {
            InitializeComponent();
        }

        private void buttonNew_Click(object sender, EventArgs e)
        {
            LibraryBookDialog dlg = new LibraryBookDialog();
            dlg.ShowDialog();

            if (dlg.DialogResult == DialogResult.OK)
            {
                listBoxLibraryBooks.Items.Add(dlg.Book);
            }
            dlg.Dispose();
        }

        private void MainForm_Load(object sender, EventArgs e)
        {
            listBoxLibraryBooks.DisplayMember = "Title";
        }
    }
}

The QUESTION: Why is it that when I add the LibraryBook book object to the listBox, I get a blank element. I mean, it is there, the element in the listBox exists, but I am not sure if the data has been passed from form to form. Why is this so?

Answer 1

You are using Book property of dialog but you’re not setting it with in the book dialog and your property getter returns a new instance if it is null. That is why you’re getting a blank entry.

    private void buttonOk_Click(object sender, EventArgs e)
    {
        if (validateData())
        {
            try
            {
                ----> LibraryBook book = new LibraryBook(); <----- this a private book of this method. 
                book.Title = textBoxTitle.Text; 
                book.Author = textBoxAuthor.Text;
                book.CopyrightYear = Convert.ToInt32(textBoxCopyrightYear.Text);
                this.DialogResult = DialogResult.OK;
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.Message, "There was an error", MessageBoxButtons.OK, MessageBoxIcon.Error);
            }
        }
    }

Either change the book declaration to

this.book = new LibraryBook();

Or at the end of creating the book set your class member book to this like so

this.book = book;