Question

I have a Windows Forms ListBox data-bound to a BindingList of business objects. The ListBox’s displayed property is a string representing the name of the business object. I have a TextBox that is not data-bound to the name property but instead is populated when the ListBox’s selected index changes, and the TextBox, upon validation, sets the business object’s name property and then uses BindingList.ResetItem to notify the BindingList‘s bound control (the ListBox) to update itself when the TextBox’s text value is changed by the user.

This works great unless the name change is only a change in case (i.e. “name” to “Name”), in which case the ListBox doesn’t get updated (it still says “name”, even though the value of the underlying business object’s name property is “Name”).

Can anyone explain why this is happening and what I should do instead? My current workaround is to use BindingList.ResetBindings, which could work for me but may not be acceptable for larger datasets.

Update 9/27/2011: Added a simple code example that reproduces the issue for me. This is using INotifyPropertyChanged and binding the textbox to the binding list. Based on How do I make a ListBox refresh its item text?

using System;
using System.ComponentModel;
using System.Windows.Forms;

namespace WinformsDataBindingListBoxTextBoxTest
{
    public partial class Form1 : Form
    {
        private BindingList<Employee> _employees;

        private ListBox lstEmployees;
        private TextBox txtId;
        private TextBox txtName;
        private Button btnRemove;

        public Form1()
        {
            InitializeComponent();

            FlowLayoutPanel layout = new FlowLayoutPanel();
            layout.Dock = DockStyle.Fill;
            Controls.Add(layout);

            lstEmployees = new ListBox();
            layout.Controls.Add(lstEmployees);

            txtId = new TextBox();
            layout.Controls.Add(txtId);

            txtName = new TextBox();
            layout.Controls.Add(txtName);

            btnRemove = new Button();
            btnRemove.Click += btnRemove_Click;
            btnRemove.Text = "Remove";
            layout.Controls.Add(btnRemove);

            Load += new EventHandler(Form1_Load);
        }

        private void Form1_Load(object sender, EventArgs e)
        {
            _employees = new BindingList<Employee>();
            for (int i = 0; i < 10; i++)
            {
                _employees.Add(new Employee() { Id = i, Name = "Employee " + i.ToString() });
            }

            lstEmployees.DisplayMember = "Name";
            lstEmployees.DataSource = _employees;

            txtId.DataBindings.Add("Text", _employees, "Id");
            txtName.DataBindings.Add("Text", _employees, "Name");
        }

        private void btnRemove_Click(object sender, EventArgs e)
        {
            Employee selectedEmployee = (Employee)lstEmployees.SelectedItem;
            if (selectedEmployee != null)
            {
                _employees.Remove(selectedEmployee);
            }
        }
    }

    public class Employee : INotifyPropertyChanged
    {
        private string name;
        private int id;

        public string Name
        {
            get { return name; }
            set
            {
                name = value;
                OnPropertyChanged("Name");
            }
        }
        public int Id
        {
            get { return id; }
            set
            {
                id = value;
                OnPropertyChanged("Id");
            }
        }

        #region INotifyPropertyChanged Members

        public event PropertyChangedEventHandler PropertyChanged;

        protected void OnPropertyChanged(string name)
        {
            PropertyChangedEventHandler handler = PropertyChanged;
            if (handler != null)
            {
                handler(this, new PropertyChangedEventArgs(name));
            }
        }

        #endregion
    }
}

Update 9/28/2011: The problem seems to be internal to the ListBox control, specifically the way it decides (not) to update an item if its string representation is equivalent to the new value, ignoring case differences. As far as I can tell this is hard coded into the control with no way to override it.

Answer 1

Think I found the problem: