UWP to WinUI Desktop - FileOpenPicker

UWP-To-WinUI-Desktop-FileOpenPicker.cs

FileOpenPicker open = new();
open.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
open.FileTypeFilter.Add("*");

WinUIConversionUtil.InitFileOpenPicker(open);

var file = await open.PickSingleFileAsync();

if (file != null)
{
    var text = await FileIO.ReadTextAsync(file);
    MessageDialog dlg = new(text);
    await dlg.ShowAsync();
}

WinUIConversionUtil.cs

public static class WinUIConversionUtil
{
    public static void InitFileOpenPicker(FileOpenPicker picker)
    {
        if (Window.Current == null)
        {
            var initializeWithWindowWrapper = picker.As<IInitializeWithWindow>();
            var hwnd = GetActiveWindow();
            initializeWithWindowWrapper.Initialize(hwnd);
        }
    }


    [ComImport, Guid("3E68D4BD-7135-4D10-8018-9FB6D9F33FA1"), InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
    public interface IInitializeWithWindow
    {
        void Initialize([In] IntPtr hwnd);
    }

    [DllImport("user32.dll", ExactSpelling = true, CharSet = CharSet.Auto, PreserveSig = true, SetLastError = false)]
    public static extern IntPtr GetActiveWindow();
}

This work ;
FileOpenPicker picker = new FileOpenPicker() { CommitButtonText = "Valider", SuggestedStartLocation = PickerLocationId.ComputerFolder, FileTypeFilter = { ".jpg", ".jpeg" } }; WinUIConversionUtil.InitFileOpenPicker(picker); StorageFile fichier = await picker.PickSingleFileAsync();

But this do not work (MultipleFile)

FileOpenPicker picker = new FileOpenPicker() { CommitButtonText = "Valider", SuggestedStartLocation = PickerLocationId.ComputerFolder, FileTypeFilter = { ".jpg", ".jpeg" } }; WinUIConversionUtil.InitFileOpenPicker(picker); IReadOnlyList<StorageFile> fichiers = await picker.PickMultipleFilesAsync();
Crash System.Reflection.TargetInvocationException: 'Exception has been thrown by the target of an invocation.'
COMException: L’application a appelé une interface qui était maintenue en ordre pour un thread différent. (0x8001010E (RPC_E_WRONG_THREAD))

Thanks, @Fernand-Delavy. I never tested with PickMultipleFilesAsync. Hopefully this will be fixed in a future WinUI version.

Sometime, will have trouble with Member 'FileOpenPicker.As<WinUIConversionUtil.IInitializeWithWindow>()' cannot be accessed with an instance reference; qualify it with a type name instead.

Import using WinRT to resolve it.