DockableBase's closing design should support async

[stevemonaco]

The current signature of DockableBase.OnClose does not lend itself well to async operations:

public virtual bool OnClose()

This is problematic when prompting the user to save/discard/cancel a modified Document tab when the close button is clicked as Avalonia's ShowDialog API is async. I have worked around this by using a synchronous dialog extension after my own attempts ended in async-related deadlocks.

Is there an alternative, intended approach that I'm missing here?

[wieslawsoltes]

If you can propose design solution it can be added in next major release.

[stevemonaco]

Sorry for the non-response, but I don't know how to design an API that lends itself well to both sync and async scenarios. Not in a way that can be consumed by Dock internally anyways. I would want to override an API like:

public virtual async Task<bool> OnCloseAsync()

I ended up taking the approach from the SyncDialogExtensions before and integrating them into the VM itself at the cost of directly referencing an Avalonia bit (Dispatcher). The VM is fairly isolated and is already tied to Dock which is tied to Avalonia, so I don't mind the break in MVVM purity too much. With AvalonDock, you didn't need wrappers like this.

public partial class DockableEditorViewModel : Document
{
    [ObservableProperty] private ResourceEditorBaseViewModel _editor;
    private readonly EditorsViewModel _editors;

    public DockableEditorViewModel(ResourceEditorBaseViewModel editor, EditorsViewModel editors)
    {
        _editor = editor;
        _editors = editors;
    }

    public override bool OnClose()
    {
        using var cts = new CancellationTokenSource();
        bool result = default;

        _editors.RequestSaveUserChanges(_editor, true).ContinueWith(x =>
            {
                result = x.IsCompletedSuccessfully && x.Result != UserSaveAction.Cancel;
                cts.Cancel();
            },
            TaskScheduler.FromCurrentSynchronizationContext());

        Dispatcher.UIThread.MainLoop(cts.Token);
        return result;
    }
}