I am developing an application in C# using WinUI3 and I am having trouble setting the parent window for a modeless dialog. By setting the parent window, I expect the following effects:

• The dialog should be displayed in front of the parent window.
• The dialog should close when the parent window is closed.

Here is the code I have tried. I used SetParent, but the dialog gets embedded within the main window, and the AppWindow of the dialog becomes null.

public sealed partial class ModelessDialog : Window
{
    public ModelessDialog(SizeInt32 windowSize, Window _parent)
    {
        this.InitializeComponent();

        OverlappedPresenter presenter = (OverlappedPresenter)this.AppWindow.Presenter;
        presenter.IsResizable = true;
        this.AppWindow.SetPresenter(presenter);
        this.AppWindow.IsShownInSwitchers = false;
        this.AppWindow.Resize(windowSize);

        IntPtr windowHandle = App.GetWindowHandle(this);
        IntPtr parentHandle = App.GetWindowHandle(_parent);
        SetParent(windowHandle, parentHandle);
    }

    public IntPtr GetWindowHandle(in Window _window)
    {
        return WinRT.Interop.WindowNative.GetWindowHandle(_window);
    }

    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);
}

I am developing an application in C# using WinUI3 and I am having trouble setting the parent window for a modeless dialog. By setting the parent window, I expect the following effects:

• The dialog should be displayed in front of the parent window.
• The dialog should close when the parent window is closed.

Here is the code I have tried. I used SetParent, but the dialog gets embedded within the main window, and the AppWindow of the dialog becomes null.

public sealed partial class ModelessDialog : Window
{
    public ModelessDialog(SizeInt32 windowSize, Window _parent)
    {
        this.InitializeComponent();

        OverlappedPresenter presenter = (OverlappedPresenter)this.AppWindow.Presenter;
        presenter.IsResizable = true;
        this.AppWindow.SetPresenter(presenter);
        this.AppWindow.IsShownInSwitchers = false;
        this.AppWindow.Resize(windowSize);

        IntPtr windowHandle = App.GetWindowHandle(this);
        IntPtr parentHandle = App.GetWindowHandle(_parent);
        SetParent(windowHandle, parentHandle);
    }

    public IntPtr GetWindowHandle(in Window _window)
    {
        return WinRT.Interop.WindowNative.GetWindowHandle(_window);
    }

    [DllImport("user32.dll", SetLastError = true)]
    public static extern IntPtr SetParent(IntPtr hWndChild, IntPtr hWndNewParent);
}

• c#
• winui-3
• winui
• windows-app-sdk

1 Answer 1

You can use the parent's Closed event to close the modeless window.

public partial class ModelessWindow : Window
{
    public ModelessWindow(SizeInt32 size, Window parent) : base()
    {
        parent.Closed += (s, e) => this.Close();

        this.AppWindow.MoveAndResize(
            new RectInt32(
                parent.AppWindow.Position.X,
                parent.AppWindow.Position.Y,
                size.Width,
                size.Height));
    }
}