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

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 2

lstBox.Items[lstBox.SelectedIndex] = lstBox.SelectedItem;