WindowsAppSDK: Preview 4 - FolderPicker and FilePicker not working / App crashes

I have just tested the small code below, and it works for me.

private async void MyButton_Click(object sender, RoutedEventArgs e)
{
  var filePicker = new FileOpenPicker();

  // Pass in the current WinUI window and get its handle
  var hwnd = WinRT.Interop.WindowNative.GetWindowHandle(this);     
  WinRT.Interop.InitializeWithWindow.Initialize(filePicker, hwnd);

  filePicker.FileTypeFilter.Add("*");

   // Now you can call methods on filePicker
  var file = await filePicker.PickSingleFileAsync();
}

Without writing Guid("3E68D4BD-7135-4D10-8018-9FB6D9F33FA1")

Wiki Call WinRT COM interop interfaces from .NET 5+ apps

I’m facing something similar and none of the solutions seem to be working for me. I’m building a WinUI 3 Desktop app on Windows 11 and in VS2019.

Code:

// Open a text file.
FileOpenPicker open = new();
open.SuggestedStartLocation = PickerLocationId.DocumentsLibrary;
open.FileTypeFilter.Add("*");

// When running on win32, FileOpenPicker needs to know the top-level hwnd via IInitializeWithWindow::Initialize.
if (Window.Current == null)
{
    IntPtr hwnd = GetActiveWindow();
    IInitializeWithWindow initializeWithWindowWrapper = FileOpenPicker.As<IInitializeWithWindow>();
    initializeWithWindowWrapper.Initialize(hwnd);
}

var files = await open.PickMultipleFilesAsync();

Exception: Specified cast is not valid.

Screenshot:

@Aloento can you explain what’s not working? Can you share your full code sample? What exception is being thrown and at what line? Make sure you’re calling this.As<IWindowNative>().WindowHandle; from a foreground UI thread from directly within a Window class (or pass your window instead of the this parameter`, you need to obtain the window handle from a Window class

There is an unhandled exception at 0x76556AB1 (combase.dll) (in Reunion.exe): 0xC000027B: An internal application exception has occurred. (Parameter: 0x1D07C6E0, 0x00000001).

using System;
using System.Runtime.InteropServices;
using Microsoft.UI.Xaml;
using Windows.Storage.Pickers;

// To learn more about WinUI, the WinUI project structure,
// and more about our project templates, see: http://aka.ms/winui-project-info.
namespace Reunion
{
    public sealed partial class MainWindow : Window
    {
        public MainWindow()
        {
            InitializeComponent();
        }

        private async void MyButton_Click(object sender, RoutedEventArgs e)
        {
            var filePicker = new FileOpenPicker();

            //Get the Window's HWND
            var hwnd = As<IWindowNative>().WindowHandle;

            //Make folder Picker work in Win32

            var initializeWithWindow = FileOpenPicker.As<IInitializeWithWindow>();
            initializeWithWindow.Initialize(hwnd);
            filePicker.FileTypeFilter.Add("*");

            var folder = await filePicker.PickSingleFileAsync();
        }

        [ComImport]
        [Guid("3E68D4BD-7135-4D10-8018-9FB6D9F33FA1")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        public interface IInitializeWithWindow
        {
            void Initialize(IntPtr hwnd);
        }
        [ComImport]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        [Guid("EECDBF0E-BAE9-4CB6-A68E-9598E1CB57BB")]
        internal interface IWindowNative
        {
            IntPtr WindowHandle { get; }
        }
    }
}

I know where is the problem. I should use using WinRT; It works fine.

Thanks for linking this issue @eleanorleffler. It seems that PickMultipleFilesAsync fails for other reasons. Let’s take care of this in the microsoft/microsoft-ui-xaml#4198 issue. Is that ok with you?

@AndyMahub The need of initializeWithWindow is a common pattern in WinRT APIs that require to specify a window that hosts the UI. It was designed in this way. The Project Reunion team is working on improving the Pickers story, but I don’t know yet whether they will simplify this. Meanwhile, we will need to live with it. Adding @ptorr-msft and for awareness,

@orapps44

I’ve tried all your proposal, unfortunnately none of them works on my side (WUINUI3 + .net 6.0).

I’m pretty disapointed to see even basics aren’t fully supported yet…

private async void LoadFromFile(object sender, RoutedEventArgs e)
{
    var fPicker = new FileOpenPicker();

    var handle = WinRT.Interop.WindowNative.GetWindowHandle(ABootstrap.Resolve<MainWindow>());
    WinRT.Interop.InitializeWithWindow.Initialize(fPicker, handle);

    fPicker.FileTypeFilter.Add("*");

    var selected = await fPicker.PickSingleFileAsync();
}

Replace ABootstrap.Resolve<MainWindow>() with a reference to your MainWindow, in my case I use dependency injection to aquire it from everywhere… you can just make a static reference if you like

I have just tested the small code below, and it works for me.

private async void MyButton_Click(object sender, RoutedEventArgs e)
{
  var filePicker = new FileOpenPicker();

  // Pass in the current WinUI window and get its handle
  var hwnd = WinRT.Interop.WindowNative.GetWindowHandle(this);     
  WinRT.Interop.InitializeWithWindow.Initialize(filePicker, hwnd);

  filePicker.FileTypeFilter.Add("*");

   // Now you can call methods on filePicker
  var file = await filePicker.PickSingleFileAsync();
}

Without writing Guid("3E68D4BD-7135-4D10-8018-9FB6D9F33FA1")

Wiki Call WinRT COM interop interfaces from .NET 5+ apps

Using WinUI3, you’d better do like this: WinRT.Interop.WindowNative.GetWindowHandle(App.MainWindow);

It appears the same work around is now required for MessageDialog. I’m still not sure I understand why this is “by-design” and if it is, I’m not sure I agree with the design. @andrewleader is there any way we can track an on-going issue to tidy this up in the long term? Surely there must be a more intuitive way so that we don’t end up with code being littered with As<IInitializeWithWindow>() calls.

@Aloento can you explain what’s not working? Can you share your full code sample? What exception is being thrown and at what line?

Make sure you’re calling this.As<IWindowNative>().WindowHandle; from a foreground UI thread from directly within a Window class (or pass your window instead of the this parameter`, you need to obtain the window handle from a Window class

@AndyMahub,

I have just tested the code below with Preview 4 bits, and it works for me.

 public sealed partial class MainWindow : Window
 {
      ...

        private async void myButton_Click(object sender, RoutedEventArgs e)
        {
            var filePicker = new FileOpenPicker();

            //Get the Window's HWND
            var hwnd = this.As<IWindowNative>().WindowHandle;

            //Make folder Picker work in Win32

            var initializeWithWindow = filePicker.As<IInitializeWithWindow>();
            initializeWithWindow.Initialize(hwnd);
            filePicker.FileTypeFilter.Add("*");

            var folder = await filePicker.PickSingleFileAsync();
            myText.Text = folder != null ? folder.Path : string.Empty;
        }

        [ComImport]
        [Guid("3E68D4BD-7135-4D10-8018-9FB6D9F33FA1")]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        public interface IInitializeWithWindow
        {
            void Initialize(IntPtr hwnd);
        }
        [ComImport]
        [InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
        [Guid("EECDBF0E-BAE9-4CB6-A68E-9598E1CB57BB")]
        internal interface IWindowNative
        {
            IntPtr WindowHandle { get; }
        }
...
}