Instantiate new object from Binding in xaml for Flyout - windows-runtime

Question

What I want to achieve may not be possible in XAML. If it is possible then its probably due to a XAML feature worth knowing. If not, then I've also learned something.
I have a button flyout which is data-bound to a view model. The view model provides a new instance of an object to the content of the flyout, via a get accessor.
Each time the button is pressed I want the flyout to present a new instance of the object.
The problem: The object is created only once, and re-presented each time the flyout is opened.
ViewModel.cs
class Item
{
public int Id { get; set; }
public string Name { get; set; }
}
class ViewModel
{
static int itemCount;
public Item GetNewItem {
get {
itemCount++;
Debug.WriteLine("Created item: " + itemCount);
return new Item() { Id = itemCount, Name = "Item_" + itemCount} ;
}
}
}
MainPage.xaml.cs
<Page.Resources>
<local:ViewModel x:Key="ViewModel"/>
</Page.Resources>
<Grid Background="{ThemeResource ApplicationPageBackgroundThemeBrush}"
DataContext="{StaticResource ViewModel}">
<Button Content="Create Item">
<Button.Flyout>
<Flyout>
<StackPanel DataContext="{Binding Path=GetNewItem}">
<TextBlock Text="{Binding Path=Id}"/>
<TextBlock Text="{Binding Path=Name}"/>
</StackPanel>
</Flyout>
</Button.Flyout>
</Button>
</Grid>
Output:
The trace statement "Created item: Item_1" appears, but not "Created Item_2", etc..
The same data ("1" and "Item_1") is presented each time the button is pressed.
Investigation
I can make it work in the code-behind of the main page. I name the grid, and add an Opening event handler to the flyout
private void Flyout_Opening(object sender, object e) {
var gridDataContext = (ViewModel)this.grid.DataContext;
this.stackPanel.DataContext = gridDataContext.GetNewItem;
}
Works fine now! (but I want to do it in XAML)
I have tried implementing INotifyPropertyChanged on the ViewModel, but this didn't work.
class ViewModel : INotifyPropertyChanged
{
static int itemCount;
public Item GetNewItem {
get {
itemCount++;
Debug.WriteLine("Created item: " + itemCount);
OnPropertyChanged("GetNewItem");
return new Item() { Id = itemCount, Name = "Item_" + itemCount} ;
}
}
public event PropertyChangedEventHandler PropertyChanged;
protected void OnPropertyChanged(string name) {
var handler = PropertyChanged;
if (handler != null) {
handler(this, new PropertyChangedEventArgs(name));
}
}