macOS file picker not working properly

[Ruben2776]

Describe the bug

The file picker on macOS in a bundled .app package is not responding properly.

When using the file picking functionality, it does not work for the first few clicks. I had to focus on another app and then back again for it to register the file picking.

It works as it should when debugging it in Rider, but the problem occurs on a bundled app version.

I have tested this with PicView with Avalonia version 12.1.x on macOS 15.7.3 and 15.6.1. It has also been reported in Ruben2776/PicView#386

I believe this is in relation to #21799. I experienced no trouble in the Avalonia 11.x versions.

The changelog for 12.1.1 mentions

macOS – Fix app activation by @JakobScholer in #21799

but it still occurs in 12.1.1.

To Reproduce

Use IStorageProvider with FolderPickerOpenOptions, FilePickerSaveOptions or FilePickerOpenOptions in a bundled app. Active either one of them, notice nothing happens. Switch to another window, and then back again and notice it works,

Expected behavior

It should be immediately responsive without having to switch to another window.

Avalonia version

12.1.1

OS

macOS

Additional context

No response

[JakobScholer]

@Ruben2776
I will give it a look later this week.
Just a couple questions to ease the hunt for me.
Does the issue occur on every launch or only sometimes? Does it occur if you click the filePicker within the first second of launching or later?
And if you can link me a simple example repo where you can reproduce the issue that would be very nice :)

[Ruben2776]

@JakobScholer Thank you for the assistance.

Clicking the file picking does consistently not respond on every single launch. Waiting changes nothing, only switching to another app/window makes the FilePicker responsive.

I don't have a simple reproduction example. It's reproducible in my open source picture viewer, PicView. You can see the App.axaml.cs where I have the startup procedure for my macOS version. For the file picker pretty much all I do is calling it via Dispatcher.UIThread.InvokeAsync(action).ConfigureAwait(false) as you can see in my FilePickerService.cs.
All this worked perfectly in the Avalonia 11.x versions, but it broke somewhere between 12.0 or 12.1 I think (I didn't have a release build for the 12.0 version on macOS).

I believe you want a minimal sample, but the problem is that is timing dependent, as you surmised in #21799. But opening a file at startup from the ProtocolActivatedEventArgs is also timing dependent. I spent a whole day testing and rebuilding my macOS version countless hours for the ProtocolActivatedEventArgs to actually firing correctly so that you could open files at startup. Which I reported in a comment here #20738 (comment).
I'm saying this (do correct me if I am wrong) because I'm afraid changing the startup procedure could fix the FilePicker, but cause the FileActivation to misfire. Being able to open files at startup is paramount to me.

[JakobScholer]

I don't think it is an Avalonia issue but an issue with your project.
I have made a PR to your project here Ruben2776/PicView#392.

[Ruben2776]

So the fix is to use

if (Application.Current.ApplicationLifetime is IClassicDesktopStyleApplicationLifetime desktop)
{
    desktop.MainWindow = mainWindow;
}

Where mainWindow is your primary window. But this is not referenced in the documentation at all. I believe it would be a good idea to to update the docs.

I, personally, think it's a mistake that setting the MainWindow in IClassicDesktopStyleApplicationLifetime forces the window to be shown. I don't know whether this is intended or not, but it is a bit confusing and makes it a bit harder if you want to, e.g., set the window size to match the size of an opened picture/document before it is shown, to avoid excessive resizing.