examples:Showcase fix higherchy navigation.

examples/demo/showcase/main.py

@@ -73,6 +73,16 @@ class ShowcaseApp(App):
         self.root.ids.sm.switch_to(self.load_screen(idx), direction='left')
         self.update_sourcecode()
 
+    def go_higherarchy_previous(self):
+        ahr = self.higherarchy
+        if len(ahr) == 1:
+            return
+        if ahr:
+            ahr.pop()
+        if ahr:\
+            idx = ahr.pop();\
+            self.go_screen(idx)
+
     def load_screen(self, index):
         if index in self.screens:
             return self.screens[index]

examples/demo/showcase/showcase.kv

@@ -52,11 +52,7 @@ BoxLayout:
             ActionPrevious:
                 with_previous: (False if sm.current_screen.name == 'button' else True) if sm.current_screen else False
                 title: 'Showcase' + ('' if not app.current_title else ' - {}'.format(app.current_title))
-                on_release:
-                    if app.higherarchy: app.higherarchy.pop()
-                    if app.higherarchy:\
-                    idx = app.higherarchy.pop();\
-                    app.go_screen(idx)
+                on_release: app.go_higherarchy_previous()
 
             ActionSpinner:
                 id: spnr