#GtkFileChooser is an interface that can be implemented by file selection widgets. In GTK+, the main objects that implement this interface are #GtkFileChooserWidget, #GtkFileChooserDialog, and #GtkFileChooserButton. You do not need to write an object that implements the #GtkFileChooser interface unless you are trying to adapt an existing file selector to expose a standard programming interface.
Fluent builder implementation template for gtk.file_chooser.FileChooser
Module for FileChooser interface