FileOpenPicker, FolderPicker and FolderPicker not available in partial trust/AppContainer

[sungaila]

Describe the bug

In WinUI 3 it is needed to do the following call to initialize a picker dialog:

WinRT.Interop.InitializeWithWindow.Initialize(openPicker, hWnd);

It works just fine in full trust mode but fails when it is called in partial trust/inside an AppContainer (access denied exception).

This is terrible news because it means that WinUI 3 can either use the WinRT file dialogs OR run in partial trust. But NOT both at the same time.

Steps to reproduce the bug

1. Create a packaged WinUI 3 app with the default template
2. Change Package.appxmanifest such that the app runs in partial mode
3. Optional: add the broadFileSystemAccess capability
4. Test the FilePicker code snippet from the WinUI 3 Gallery: winui3gallery://item/FilePicker

Expected behavior

The file dialogs should open just as expected.

Screenshots

No response

NuGet package version

WinUI 3 - Windows App SDK 1.5.2: 1.5.240404000

Windows version

Windows 11 (22H2): Build 22621

Additional context

No response

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[Rybasum]

This issue is several years old and it looks like Microsoft simply does not want us to put non-UWP apps in AppContainer. Otherwise they would realize that most UI apps use file open/save pickers. AppContainer? yes, sure, but no file open/save. Very strange. Honestly, they should simply document this and not make developers waste their time.

[sungaila]

@Rybasum The documentation part is kinda confusing. There is in-depth documentation on how to put your WPF, WinForms or WinUI 3 app into an AppContainer using MSIX. Yet something fundamental like selecting files isn't possible with Win32 or WinRT APIs.

I have a simple WinUI 3 app here where the user selects a file and more information is put into a DataGrid. You'd think that it would be a perfect candidate for partial trust/AppContainer and just the filesystem capability.

[mominshaikhdevs]

@sungaila you want to see

https://github.com/microsoft/WindowsAppSDK/issues/8#issuecomment-2256000803

and https://github.com/microsoft/WindowsAppSDK/issues/219

and the win32-app-isolation repo.