Interface casting issues when an unknown type is returned

[cameronwhite]

I ran into an interesting scenario with the following code to try obtain a Gio.File from the Gio.ListModel returned by Gtk.FileChooser.GetFiles()

Gtk.FileChooserDialog file_chooser = ... // open some files with a file chooser

Gio.ListModel files = file_chooser.GetFiles ();
for (uint i = 0, n = files.GetNItems (); i < n; ++i) {
	// The runtime type is just a GObject.Object instance
	// The gtype is 'GLocalFile' which is a private type that inherits from GObject and implements the 'GFile' interface
	GObject.Object? obj = files.GetObject (i);
        var file = obj as Gio.File; // fails
}

The GObject returned is of type GLocalFile which isn't public, so there isn't a C# type to create an instance of. The ObjectWrapper then just creates an instance of the parent class, GObject.Object in this case.
This presents a problem with trying to cast to a Gio.File interface, since the C# object doesn't have a runtime type that implements that interface

Perhaps some sort of cast function that checks the gtype is needed?
My manual workaround was to do var file = new Gio.FileHelper (files.GetObject (i).Handle, ownedRef: true), although that doesn't do any safe type checking

[badcel]

For classes which implement interfaces inside list models this should already work For private classes which implement interfaces not.

Your suggestion using a method to cast the list items we could return an IEnumarable<T> which either casts a class to a more concrete class/interface or wraps the instance into an interface wrapper and checks the type if the gobject class is simply GObject but a more concrete type is required and confirmed by the list model.

Perhaps an additional method to get a casted single item would be helpful, too.

[cameronwhite]

Yeah, getting an IEnumerable<T> that does casting if necessary sounds like a good way to go. Even for cases that don't hit this interface casting issue, it would be a more C#-style API than having to use the GetNItems() to iterate over the list

[badcel]

#588 will help with integrating native types with some dotnet interfaces.

To return the correct type from a given pointer the type detection will be improved as part of #1118.