Binding List to ItemsControl: How to refresh

Question

I am binding a List to an ItemsControl. I shows up fine. But when I add a string to the list the control is not updated. I tried to raise the PropertyChanged event to force the update but that does not help. What am I doing wrong?

Here is the XAML:

<Window x:Class="tt.MainWindow"
    xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
    xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
    Title="MainWindow" Height="350" Width="525">
<StackPanel>
    <ItemsControl ItemsSource="{Binding Strings}"/>
    <Button Click="Button_Click">Add</Button>
</StackPanel>
</Window>

Here is the code behind:

 public partial class MainWindow : Window, INotifyPropertyChanged
{
    public event PropertyChangedEventHandler PropertyChanged;
    public MainWindow()
    {
        InitializeComponent();
        DataContext = this;
        Strings.Add("One");
        Strings.Add("Two");
    }

    public List<string> _strings = new List<string>();
    public List<string> Strings
    {
        get { return _strings; }
        set
        {
            if (_strings == value) return;
            _strings = value;
            if (this.PropertyChanged != null)
                PropertyChanged(this, new PropertyChangedEventArgs("Strings"));
        }
    }

    private void Button_Click(object sender, RoutedEventArgs e)
    {
        Strings.Add("More");
        if (this.PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs("Strings"));
    }
}

Answer 1

Change List<string> to ObservableCollection<string> (msdn).

public ObservableCollection<string> _strings = new ObservableCollection<string>();
public ObservableCollection<string> Strings
{
    get { return _strings; }
    set
    {
        if (_strings == value) return;
        _strings = value;
        if (this.PropertyChanged != null)
            PropertyChanged(this, new PropertyChangedEventArgs("Strings"));
    }
}