InvalidCastException when trying to get string array from ApplicationData

[tipa]

Describe the bug

When building the app with PublishAot=true, getting a string array from ApplicationData.Current.LocalSettings and casting it to the string[] type I get:
System.InvalidCastException: 'Unable to cast object of type 'WinRT.IInspectable' to type 'System.String[]'.'

Steps to reproduce the bug

Set in csproj:
<PublishAot>true</PublishAot>

ApplicationData.Current.LocalSettings.Values["test"] = new string[] { "a", "b", "c" };
var array = (string[])ApplicationData.Current.LocalSettings.Values["test"];

Expected behavior

No crash

Screenshots

NuGet package version

Windows App SDK 1.6.0: 1.6.240829007

Packaging type

Packaged (MSIX)

Windows version

Windows 11 version 22H2 (22621, 2022 Update)

IDE

Visual Studio 2022

Additional context

Example project: Test.zip

[fabianoriccardi]

I think I met the same/related issue on another example (WASDK v1.6, AOT enabled):

SelectionChangedEventArgs args = new([], []);

Throws invalidcastexception: "specified cast is not valid".

[Scottj1s]

Manodasan Wignarajah (@manodasanW) Does this look related to the collection expression marshaling issue?

[tipa]

I'm also seeing crashes when setting an IEnumerable as ItemSource, like this:
comboBox.ItemsSource = Enumerable.Range(0, 10).Select(x => new TestItem(x));
No crash when using .ToList()
comboBox.ItemsSource = Enumerable.Range(0, 10).Select(x => new TestItem(x)).ToList();

If this is a separate issue and you want me to open a new issue, please let me know

[tipa]

Any hope this will be resolved with the next release? It's the only thing blocking me from using NativeAot.

[tipa]

The problem still happens with 1.7.250109001-experimental2

[Sergio0694]

"I'm also seeing crashes when setting an IEnumerable as ItemSource, like this:
comboBox.ItemsSource = Enumerable.Range(0, 10).Select(x => new TestItem(x));"

That's expected and not supported. You need either ToList() or ToString().

[Sergio0694]

Can repro with CsWinRT 2.2.0, only if PublishAot is set. Otherwise the cast works (both to string[] and interfaces).

[dongle-the-gadget]

If this helps, we should look into ComWrappersSupport. GetRuntimeClassForTypeCreation and TypeNameSupport. They determine which type the return value is, and it's woefully incomplete for AOT scenarios.

[GuildOfCalamity]

Just ran into something similar using a FlipView with an ObservableCollection<string> as the ItemsSource. The only way to get around it was to set the AllowUnsafeBlocks to true in the csproj - weird.

System.InvalidCastException: 'Unable to cast object of type 'WinRT.IInspectable' to type 'System.String[]'.'

[Sergio0694]

That's expected and by design. If you use CsWinRT 2.2.0 you'll get a proper warning telling you to enable that.

[tipa]

I've reported this issue six months ago. Is there any hope this will get fixed any time soon? It's the only blocker that prevents me using Native AOT for this particular app. Should I just JSON-serialize my string array and write the resulting string to my local app settings? It will be a pain migrating my users, but I don't see any progress here...

[GuildOfCalamity]

Timo Partl (@tipa) I had to do the json serialize/deserialize workaround as well, not sure how this was overlooked in the first place?
Setting a collection as a source is a VERY common routine. People claiming it's "by design" - I don't buy that excuse.
I guess the other question becomes How to properly cast a 'System.String[]' to 'WinRT.IInspectable' if the BCL is unable to perform this step natively? Furthermore, dynamic binding would appear to be the root cause due to the performance AOT is claiming?