Launch an application to open the file.
This may present an app chooser dialog to the user.
The callback will be called when the operation is completed. It should call gtk.file_launcher.FileLauncher.launchFinish to obtain the result.
the parent gtk.window.Window
a gio.cancellable.Cancellable to cancel the operation
a callback to call when the operation is complete
Launch an application to open the file.
This may present an app chooser dialog to the user.
The callback will be called when the operation is completed. It should call gtk.file_launcher.FileLauncher.launchFinish to obtain the result.