[WindowsDesktop] `OpenFileDialog.ShowDialog()` hangs with `return await rootCommand.InvokeAsync(args);`

[abdeldjalil-fellah]

OpenFileDialog.ShowDialog() hangs in MainForm with:

[STAThread]
static async Task<int> Main(string[] args)
{
            var rootCommand = new RootCommand();
            rootCommand.SetHandler((context) =>
            {
                Application.Run(new MainForm());
            });
            return await rootCommand.InvokeAsync(args);
}

but works well with:

[STAThread]
static int Main(string[] args)
{
            var rootCommand = new RootCommand();
            rootCommand.SetHandler((context) =>
            {
                Application.Run(new MainForm());
            });
            return rootCommand.Invoke(args);
}

[KalleOlaviNiemitalo]

Does it work if you install a WindowsFormsSynchronizationContext on the thread before you use System.CommandLine? I mean, if System.CommandLine calls your handler from an async task, then there's no guarantee that the task runs on your original STA thread, unless you set the synchronization context first.

It might be safest to make the handler create and start a new thread for the Windows Forms stuff, with Thread.SetApartmentState(ApartmentState.STA) in between.

[abdeldjalil-fellah]

yes, the problem is fixed by replacing Application.Run(new MainForm()); by:

var thread = new Thread(() => Application.Run(new MainForm()));
thread.SetApartmentState(ApartmentState.STA);
thread.Start();
thread.Join();