WinForms: ListBox item updates case insensitive?

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:

Answer 2

I just hope this concept will be helpfull to solve your problem

I have a TextBox, the user input is compared to string "Name". My button click event is:

private void btn_Click(object sender, EventArgs e)
{
  if(txt.Text == "Name")
     MessageBox.Show("Value is Same");
}

If you write "name" in textbox, condition will be false. If you type type "Name" in textbox, condition will be true. Now try changing the btn click:

using System.Globalization;
private void btn_Click(object sender, EventArgs e)
{
        TextInfo ChangeCase = new CultureInfo("en-US", false).TextInfo;
        string newText = ChangeCase.ToTitleCase(txt.Text);

        if (newText == "Name")
            MessageBox.Show("Value is Same");
}

now you type "name" or "Name" condition is true. Remember it will just capaitalize the first letter of the string suplied. "my name" will outputted as "My Name".

And if your condition says:

if(txt.Text == "name")
   MessageBox.Show(Value is Same);

Then you can try something like

string newText = (txt.Text).ToLower();
if(newText == "name")
   MessageBox.Show(Value is Same);

Here the supplied string will outputted in the lower case always. Hope it helps.

Answer 3

This really is the same problem as when renaming files or directories while only case is different. I suggest the same work-around that I found earlier:

if (oldValue.ToUpper() == newValue.ToUpper()){
ListBox1.Items[i] = newValue + "_tmp";  // only adding stuff to force an update
ListBox1.Items[i] = newValue;     // now the new value is displayed, even only case has changed
}

Now for your question, I suggest you try to check if the setter is changing a value only in lower/upper case (a.ToUpper() == b.ToUpper()). If true, then first give a extra change, before the intended change, something like:

name = value + "_tmp";
OnPropertyChanged("Name");
name = value;
OnPropertyChanged("Name");

Hope this helps.