Port 'Navigation View' demo to Python (#87)

demos/Navigation View/main.py

@@ -0,0 +1,33 @@
+import workbench
+
+nav_view = workbench.builder.get_object("nav_view")
+nav_pageone = workbench.builder.get_object("nav_pageone")
+next_button = workbench.builder.get_object("next_button")
+previous_button = workbench.builder.get_object("previous_button")
+nav_pagetwo = workbench.builder.get_object("nav_pagetwo")
+nav_pagethree = workbench.builder.get_object("nav_pagethree")
+nav_pagefour = workbench.builder.get_object("nav_pagefour")
+title = workbench.builder.get_object("title")
+
+
+def on_next_button_clicked(_button):
+    page = nav_view.get_visible_page()
+    if page == nav_pageone:
+        nav_view.push(nav_pagetwo)
+    elif page == nav_pagetwo:
+        nav_view.push(nav_pagethree)
+    elif page == nav_pagethree:
+        nav_view.push(nav_pagefour)
+
+
+def on_page_changed(_view, _visible_page):
+    previous_button.set_sensitive(nav_view.get_visible_page() != nav_pageone)
+    next_button.set_sensitive(nav_view.get_visible_page() != nav_pagefour)
+    title.set_label(nav_view.get_visible_page().get_title())
+
+
+next_button.connect("clicked", on_next_button_clicked)
+
+previous_button.connect("clicked", lambda _: nav_view.pop())
+
+nav_view.connect("notify::visible-page", on_page_changed)