Application
Creates a new GtkApplication instance.
When using GtkApplication, it is not necessary to call func@Gtk.init manually. It is called as soon as the application gets registered as the primary instance.
Concretely, func@Gtk.init is called in the default handler for the GApplication::startup signal. Therefore, GtkApplication subclasses should always chain up in their GApplication::startup handler before using any GTK API.
Note that commandline arguments are not passed to func@Gtk.init.
If application_id is not null, then it must be valid. See g_application_id_is_valid().
If no application ID is given then some features (most notably application uniqueness) will be disabled.
Return
a new GtkApplication instance
Parameters
applicationId
The application ID
flags
the application flags
constructor(pointer: <Error class: unknown class><<Error class: unknown class>>)