Add Async FontDialog methods and sample

[kashifsoofi]

Added manual binding for FontDialog Async methods.

• ChooseFaceAsync
• ChooseFamilyAsync
• ChooseFontAsync

Added a sample application to use ChooseFontAsync function.

• I agree that my contribution may be licensed either under MIT or any version of LGPL license.

[badcel]

Thanks for your contribution. At a first glance the code looks good 👍

Some minor remarks:

• Is there a reason you use a regular Button over a FontDialogButton in your sample?
• Please don't add a new solution to the project, but add your sample project into the existing solution. The path inside the solution would be Samples/Gtk-4.0/
• Please add your sample to https://github.com/gircore/gir.core/blob/main/src/GirCore.Libs.slnf, too.

If you change your code please Ammend your code, to avoid creating additional commits.

[kashifsoofi]

Thanks for the quick review.
Sorry I missed the new sln file, was added by VSCode :(
No specific reason for using regular Button, I could already use the FontDialogButton, Not a real world scenario, I just wanted to show an alternate way of choosing font in a tutorial.
Commit updated

[badcel]

Can you add your sample to the solution file inside the Samples/Gtk-4.0 virtual folder?

[kashifsoofi]

Can you add your sample to the solution file inside the Samples/Gtk-4.0 virtual folder?

Done

[badcel]

I took a detailed look into your PR and found an issue with ChooseFontAsync: According to the docs the finish method can return Null: https://docs.gtk.org/gtk4/method.FontDialog.choose_font_finish.html

Therefore I think the code must look like:

public Task<Pango.FontDescription?> ChooseFontAsync(Window parent, Pango.FontDescription? fontDescription)
{
    var tcs = new TaskCompletionSource<Pango.FontDescription?>();

    var callbackHandler = new Gio.Internal.AsyncReadyCallbackAsyncHandler((sourceObject, res, data) =>
    {
        if (sourceObject is null)
        {
            tcs.SetException(new Exception("Missing source object"));
            return;
        }

        var fontDescriptionOwnedHandle = Internal.FontDialog.ChooseFontFinish(sourceObject.Handle, res.Handle, out var error);

        if (!error.IsInvalid)
            tcs.SetException(new GLib.GException(error));
        else
        {
            if (fontDescriptionOwnedHandle.IsInvalid)
                tcs.SetResult(null);
            else
            {
                var result = new Pango.FontDescription(fontDescriptionOwnedHandle);
                tcs.SetResult(result);   
            }
        }
    });

    var initialValue = (Pango.Internal.FontDescriptionHandle?) fontDescription?.Handle ?? Pango.Internal.FontDescriptionUnownedHandle.NullHandle;
    Internal.FontDialog.ChooseFont(
        Handle,
        parent.Handle,
        initialValue,
        IntPtr.Zero,
        callbackHandler.NativeCallback,
        IntPtr.Zero
    );

    return tcs.Task;
}

I'm not sure if your sample can be considered complete. If a user presses cancel, it means that a "recoverable error" occurred. Which in C# is an exception. I already asked the gnome devs regarding this behaviour. They argument that "if the user is expected to select a font, not doing so is an error".

So if you press cancel in the font chooser the sample app crashes. I'm not sure if or how you want to attribute to this behaviour or just add some comment?

One possible way to fix this would be:

buttonSelectFont.OnClicked += async (_, _) =>
{
    try
    {
        var fontDialog = Gtk.FontDialog.New();
        var selectedFont = await fontDialog.ChooseFontAsync(window, null);
        labelSelectedFont.SetLabel(selectedFont?.ToString() ?? string.Empty);
    }
    catch (Exception ex)
    {
        //Prints "Dismissed by user" if dialog is cancelled
        Console.WriteLine(ex.Message);
    }
};

Do you have another proposal how to attribute to the possible exception?

If those points are fixed, it is good to go 👍

[kashifsoofi]

Thanks for the detailed review, I have updated as suggested.

[badcel]

I think you missed the nullable annotations for the return type and the task completion source in ChooseFontAsync.

There should be a warning in your ide in the line tcs.SetResult(null).

[badcel]

Sorry to bother you even more. In the sample the nullable handling is missing, too: labelSelectedFont.SetLabel(selectedFont?.ToString() ?? string.Empty);

[kashifsoofi]

No bother at all, done, Thanks