Binding List to ItemsControl: How to refresh - wpf

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"));
}
}