WPF UI AddIn not updating its size

Question

I've been trying to pass a UserControl through AppDomain boundaries and noticed a weird behavior with FrameworkElementAdapters.ViewToContractAdapter() and ContractToViewAdapter(). After the INativeHandleContract has been converted back to a FrameworkElement using FrameworkElementAdapters.ContractToViewAdapters(), the wrapped UserControl doesn't change its size anymore if one of its children grows.

This behavior can be easily demonstrated using a simple, empty, WPF window:

public partial class MainWindow : Window
{
    private ListBox listBox;
    private Button myButton;

    public MainWindow()
    {
        InitializeComponent();

        listBox = new ListBox();
        Content = listBox;

        myButton = new Button { Content = "Click me" };
        myButton.Click += (sender, args) => myButton.Content = "Lorem ipsum dolor sit amet.";
        myButton.SizeChanged += (sender, args) => Debug.WriteLine($"{myButton.DesiredSize}");
        //listBox.Items.Add(myButton);

        var frameworkElement = FrameworkElementAdapters.ContractToViewAdapter(FrameworkElementAdapters.ViewToContractAdapter(myButton));
        listBox.Items.Add(frameworkElement);
    }
}

If you click the button, the text changes as expected. the button doesn't resize itself, though, which leaves you with a truncated text. If you comment out the last two lines and just add the button, it will work as expected.

I think its basically the same problem as in this case, but there doesn't seem to be a solution. Does anyone have an idea how to get rid of this?

Thanks in advance!

Answer 1

As mentioned in my comment, additionally wrapping everything in a Grid seems to do the trick or, at least, allows you to receive a SizeChanged event which you can then use to resize the resulting FrameworkElement.

public partial class MainWindow : Window
{
    private ListBox listBox;
    private Button myButton;
    private Grid dummyGrid;

    public MainWindow()
    {
        InitializeComponent();

        listBox = new ListBox();
        Content = listBox;

        myButton = new Button { Content = "Click me" };
        myButton.Click += (sender, args) =>
        {
            myButton.Content = "Lorem ipsum dolor sit amet.";
            myButton.FontSize = 24;
        };

        dummyGrid = new Grid();
        dummyGrid.ColumnDefinitions.Add(new ColumnDefinition() { Width = GridLength.Auto });
        dummyGrid.RowDefinitions.Add(new RowDefinition() { Height = GridLength.Auto });
        dummyGrid.Children.Add(myButton);

        var frameworkElement =
            FrameworkElementAdapters.ContractToViewAdapter(
                FrameworkElementAdapters.ViewToContractAdapter(dummyGrid));
        listBox.Items.Add(frameworkElement);

        // Automatically adjust HwndHost's size when the grid changes
        dummyGrid.SizeChanged += (sender, args) =>
        {
            frameworkElement.Width = args.NewSize.Width;
            frameworkElement.Height = args.NewSize.Height;
        };            
    }
}

In my case i had to do some magic to get the event to pass through the AppDomain boundaries (e.g. SizeChangedEventArgs not beeing serializable etc.).