Question

I am relatively new to binding in win forms. In order to learn the subject I setup the following test application. A basic winform with a ListBox and a Button.

public partial class Form1 : Form
{
    public List<String> stringList = new List<String>();

    public Form1()
    {
        InitializeComponent();
        stringList.Add("First");
        listBox1.DataSource = stringList;
    }

    private void button1_Click(object sender, EventArgs e)
    {
        stringList.Add("Second");
    }
}

The string “First” shows in listBox1 on application launch. However, when I push the button which adds a new string to the stringList the new item is not shown in listBox1. Could anyone help me understand the basics of collection data binding?

Answer 1

Replace List<String> with BindingList<String>.

The BindingList class can be used as a base class to create a two-way data-binding mechanism. BindingList provides a concrete, generic implementation of the IBindingList interface.

List<T> class does not provide any notification about collection changes. So there is no way ListBox would know that a new element is added. However, if you use a collection that implements IBindingList Interface, ListBox subscribes to ListChanged event. This is how it know when to refresh itself.