[gdk.global.parseArgs], [gdk.global.init_], or [gdk.global.initCheck] must have been called first.
DisplayManager.get
Gets the singleton #GdkDisplayManager object.
When called for the first time, this function consults the GDK_BACKEND environment variable to find out which of the supported GDK backends to use (in case GDK has been compiled with multiple backends). Applications can use [gdk.global.setAllowedBackends] to limit what backends can be used.
Returns
The global #GdkDisplayManager singleton;