Windows.Storage.Pickers.FileSavePicker.FileTypeChoices.Add throw System.InvalidCastException: 'Specified cast is not valid.' with PublishAOT=true

[optsing]

Describe the bug

Windows.Storage.Pickers.FileSavePicker.FileTypeChoices.Add throw System.InvalidCastException: 'Specified cast is not valid.' with PublishAOT=true
With PublishAOT=false everything works fine.

Steps to reproduce the bug

1. Create new WinAppSDK project
2. Add <WindowsSdkPackageVersion>10.0.22621.45</WindowsSdkPackageVersion> and <PublishAot>true</PublishAot> to csproj
3. Add to myButton_Click

var picker = new Windows.Storage.Pickers.FileSavePicker();
WinRT.Interop.InitializeWithWindow.Initialize(picker, WinRT.Interop.WindowNative.GetWindowHandle(this));
picker.FileTypeChoices.Add("Text file", [".txt"]);
picker.SuggestedStartLocation = Windows.Storage.Pickers.PickerLocationId.DocumentsLibrary;
var file = await picker.PickSaveFileAsync();

Expected behavior

After clicking on the button, the Save File dialog box should be displayed

Screenshots

No response

NuGet package version

Windows App SDK 1.6.0: 1.6.240829007

Packaging type

Packaged (MSIX)

Windows version

Insider Build (xxxxx)

IDE

Visual Studio 2022-preview

Additional context

No response

[mryderie]

Can anybody suggest a workaround for this? Our project needs both the file save picker and AOT, so this bug is a showstopper for us.

[optsing]

Can anybody suggest a workaround for this? Our project needs both the file save picker and AOT, so this bug is a showstopper for us.

You can call the file save picker via win32 api as described at the end of this article: https://learn.microsoft.com/en-us/uwp/api/windows.storage.pickers.filesavepicker?view=winrt-26100

To make the CsWin32 package work with AOT you need to specify “allowMarshaling”: false in NativeMethods.json and correct the original example a bit.

[mryderie]

@optsing Awesome! Works great, thank you.

[michalleptuch]

I had the same problem and modified this line:

fileSavePicker.FileTypeChoices.Add("Test file", new List<string> { ".test" });

to this:

fileSavePicker.FileTypeChoices.Add("Test file", new[] { ".test" });

and it works.

More info:
<WindowsSdkPackageVersion>10.0.26100.45</WindowsSdkPackageVersion>
<PublishAot>true</PublishAot>
<PackageReference Include="Microsoft.Windows.CsWinRT" Version="2.1.6" />
<PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.26100.1742" />
<PackageReference Include="Microsoft.WindowsAppSDK" Version="1.6.240923002" />

[optsing]

I had the same problem and modified this line:

fileSavePicker.FileTypeChoices.Add("Test file", new List<string> { ".test" });

to this:

fileSavePicker.FileTypeChoices.Add("Test file", new[] { ".test" });

and it works.

More info: <WindowsSdkPackageVersion>10.0.26100.45</WindowsSdkPackageVersion> <PublishAot>true</PublishAot> <PackageReference Include="Microsoft.Windows.CsWinRT" Version="2.1.6" /> <PackageReference Include="Microsoft.Windows.SDK.BuildTools" Version="10.0.26100.1742" /> <PackageReference Include="Microsoft.WindowsAppSDK" Version="1.6.240923002" />

Does it work in a new blank project? I have it working in a large project, even with collection expression, but it doesn't work in a smaller or empty one, even with string array or List<string>

[michalleptuch]

@optsing

Does it work in a new blank project? I have it working in a large project, even with collection expression, but it doesn't work in a smaller or empty one, even with string array or List

Unfortunately no, it doesn't. I started migrating one of my apps from .NET Native to .NET 9 (UWP) and my workaround doesn't work at all.

I haven’t checked it in an empty Windows App SDK project yet.

[optsing]

@optsing

Does it work in a new blank project? I have it working in a large project, even with collection expression, but it doesn't work in a smaller or empty one, even with string array or List

Unfortunately no, it doesn't. I started migrating one of my apps from .NET Native to .NET 9 (UWP) and my workaround doesn't work at all.

I haven’t checked it in an empty Windows App SDK project yet.

This is a common bug for UWP NET and WindowsAppSDK and was solved in CSWinRT 2.2. So the actual solution is to add a reference to the CSWinRT package version >= 2.2 for both types of projects.

I think this issue should be open as long as this bug is present in a blank project.

[DinahK-2SO]

Dear developers, thank you all for your investigation.

Combining solutions and our local test results, here is a two-step workaround for this issue:

1. Upgrade CsWinrt to version >= 2.2.
2. Add a type casting, for instance, changing picker.FileTypeChoices.Add("Test file", [ ".txt" ]); to
   picker.FileTypeChoices.Add("Test file", new List<string> { ".txt" });

This workaround works both for Windows.Storage.Pickers and Microsoft.Windows.Storage.Pickers