How do I make a ListBox refresh its item text?

Question

I'm making an example for someone who hasn't yet realized that controls like ListBox don't have to contain strings; he had been storing formatted strings and jumping through complicated parsing hoops to get the data back out of the ListBox and I'd like to show him there's a better way.

I noticed that if I have an object stored in the ListBox then update a value that affects ToString, the ListBox does not update itself. I've tried calling Refresh and Update on the control, but neither works. Here's the code of the example I'm using, it requires you to drag a listbox and a button onto the form:

Public Class Form1

    Protected Overrides Sub OnLoad(ByVal e As System.EventArgs)
        MyBase.OnLoad(e)

        For i As Integer = 1 To 3
            Dim tempInfo As New NumberInfo()
            tempInfo.Count = i
            tempInfo.Number = i * 100
            ListBox1.Items.Add(tempInfo)
        Next
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        For Each objItem As Object In ListBox1.Items
            Dim info As NumberInfo = DirectCast(objItem, NumberInfo)
            info.Count += 1
        Next
    End Sub
End Class

Public Class NumberInfo

    Public Count As Integer
    Public Number As Integer

    Public Overrides Function ToString() As String
        Return String.Format("{0}, {1}", Count, Number)
    End Function
End Class

I thought that perhaps the problem was using fields and tried implementing INotifyPropertyChanged, but this had no effect. (The reason I'm using fields is because it's an example and I don't feel like adding a few dozen lines that have nothing to do with the topic I'm demonstrating.)

Honestly I've never tried updating items in place like this before; in the past I've always been adding/removing items, not editing them. So I've never noticed that I don't know how to make this work.

So what am I missing?

Answer 1

Use the datasource property and a BindingSource object in between the datasource and the datasource property of the listbox. Then refresh that.

update added example.

Like so:

Public Class Form1

    Private datasource As New List(Of NumberInfo)
    Private bindingSource As New BindingSource

    Protected Overrides Sub OnLoad(ByVal e As System.EventArgs)
        MyBase.OnLoad(e)

        For i As Integer = 1 To 3
            Dim tempInfo As New NumberInfo()
            tempInfo.Count = i
            tempInfo.Number = i * 100
            datasource.Add(tempInfo)
        Next
        bindingSource.DataSource = datasource
        ListBox1.DataSource = bindingSource
    End Sub

    Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
        For Each objItem As Object In datasource
            Dim info As NumberInfo = DirectCast(objItem, NumberInfo)
            info.Count += 1
        Next
        bindingSource.ResetBindings(False)
    End Sub
End Class

Public Class NumberInfo

    Public Count As Integer
    Public Number As Integer

    Public Overrides Function ToString() As String
        Return String.Format("{0}, {1}", Count, Number)
    End Function
End Class

Answer 2

I dont know much about vb.net but in C# you should use datasource and then bind it by calling listbox.bind() would do the trick

Answer 3

If you derive from ListBox there is the RefreshItem protected method you can call. Just re-expose this method in your own type.

public class ListBox2 : ListBox {
 public void RefreshItem2(int index) {
  RefreshItem(index);
 }
}

Then change your designer file to use your own type (in this case, ListBox2).

Answer 4

I use this class when I need to have a list box that updates.

Update the object in the list and then call either of the included methods, depending on if you have the index available or not. If you are updating an object that is contained in the list, but you don't have the index, you will have to call RefreshItems and update all of the items.

public class RefreshingListBox : ListBox
{
    public new void RefreshItem(int index)
    {
        base.RefreshItem(index);
    }

    public new void RefreshItems()
    {
        base.RefreshItems();
    }
}

Answer 5

It's little bit unprofessional, but it works. I just removed and added the item (also selected it again). The list was sorted according to "displayed and changed" property so, again, was fine for me. The side effect is that additional event (index changed) is raised.

if (objLstTypes.SelectedItem != null)
{
 PublisherTypeDescriptor objType = (PublisherTypeDescriptor)objLstTypes.SelectedItem;
 objLstTypes.Items.Remove(objType);
 objLstTypes.Items.Add(objType);
 objLstTypes.SelectedItem = objType;
}

Answer 6

If objLstTypes is your ListBox name Use objLstTypes.Items.Refresh(); Hope this works...

Answer 7

BindingList handles updating the bindings by itself.

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

namespace TestBindingList
{
    public class Employee
    {
        public string Name { get; set; }
        public int Id { get; set; }
    }

    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);
            }
        }
    }
}