Databinding an ArrayList to a ListBox in VB.NET? - vb.net

Question

I'm working in VB.NET
I have an ArrayList named Invoices populated with objects of the class Invoice.
I'd like to data bind this to a ListBox so that as the contents of the ArrayList are updated and changed the ListBox updates. I've implemented a .ToString function on the Invoice class, I just don't know how I'd go about binding the ArrayList to the ListBox.
Any suggestions?

Answer 1

I'm going to make the assumption that this is winforms.
If you want two-way data-binding, you need a few things:
to detect addition/removal etc, you need a data-source that implements IBindingList; for classes, BindingList<T> is the obvious choice (ArrayList simply won't do...)
to detect changes to properties of the objects, you need to implement INotifyPropertyChanged (normally you can use the "*Changed" pattern, but this isn't respected by BindingList<T>)
Fortunately, ListBox handles both of these. A full example follows; I've used C#, but the concepts are identical...
using System;
using System.ComponentModel;
using System.Windows.Forms;
class Data : INotifyPropertyChanged{
private string name;
public string Name
{
get { return name; }
set { name = value; OnPropertyChanged("Name"); }
}
public event PropertyChangedEventHandler PropertyChanged;
protected virtual void OnPropertyChanged(string propertyName)
{
PropertyChangedEventHandler handler = PropertyChanged;
if (handler != null) handler(this,
new PropertyChangedEventArgs(propertyName));
}
}
static class Program
{
[STAThread]
static void Main()
{
Application.EnableVisualStyles();
Button btn1, btn2;
BindingList<Data> list = new BindingList<Data> {
new Data { Name = "Fred"},
new Data { Name = "Barney"},
};
using (Form frm = new Form
{
Controls =
{
new ListBox { DataSource = list, DisplayMember = "Name",
Dock = DockStyle.Fill},
(btn1 = new Button { Text = "add", Dock = DockStyle.Bottom}),
(btn2 = new Button { Text = "edit", Dock = DockStyle.Bottom}),
}
})
{
btn1.Click += delegate { list.Add(new Data { Name = "Betty" }); };
btn2.Click += delegate { list[0].Name = "Wilma"; };
Application.Run(frm);
}
}
}