improve handling of showing/hiding for more elements

pygame_gui/elements/ui_drop_down_menu.py

@@ -666,7 +666,10 @@ def __init__(self,
                  *,
                  expand_on_option_click: bool = True
                  ):
-
+        # Need to move some declarations early as they are indirectly referenced via the ui element
+        # constructor
+        self.menu_states = None
+        self.current_state = None
         super().__init__(relative_rect, manager, container=container,
                          starting_height=0,
                          anchors=anchors,
@@ -971,8 +974,8 @@ def show(self):
         showing it's buttons.
         """
         super().show()
-
-        self.menu_states['closed'].show()
+        if self.current_state is not None and self.menu_states is not None:
+            self.menu_states['closed'].show()
 
     def hide(self):
         """
@@ -981,7 +984,7 @@ def hide(self):
         call the hide() method of the 'closed' state which hides all it's children widgets.
         """
         super().hide()
-
-        if self.current_state == self.menu_states['expanded']:
-            self.menu_states['expanded'].hide()
-        self.menu_states['closed'].hide()
+        if self.current_state is not None and self.menu_states is not None:
+            if self.current_state == self.menu_states['expanded']:
+                self.menu_states['expanded'].hide()
+            self.menu_states['closed'].hide()

pygame_gui/elements/ui_horizontal_scroll_bar.py

@@ -578,8 +578,8 @@ def show(self):
         will propagate and show all the buttons.
         """
         super().show()
-
-        self.button_container.show()
+        if self.button_container is not None:
+            self.button_container.show()
 
     def hide(self):
         """

pygame_gui/elements/ui_horizontal_slider.py

@@ -44,7 +44,8 @@ def __init__(self,
                  visible: int = 1,
                  click_increment: Union[float, int] = 1
                  ):
-
+        # Need to move some declarations early as they are indirectly referenced via the ui element
+        # constructor
         self.sliding_button = None
         self.button_container = None
         super().__init__(relative_rect, manager, container,
@@ -560,8 +561,8 @@ def show(self):
         the button_container which will propagate and show the left and right buttons.
         """
         super().show()
-
-        self.sliding_button.show()
+        if self.sliding_button is not None:
+            self.sliding_button.show()
         if self.button_container is not None:
             self.button_container.show()
 

pygame_gui/elements/ui_panel.py

@@ -53,7 +53,9 @@ def __init__(self,
                  anchors: Optional[Dict[str, Union[str, UIElement]]] = None,
                  visible: int = 1
                  ):
-
+        # Need to move some declarations early as they are indirectly referenced via the ui element
+        # constructor
+        self.panel_container = None
         super().__init__(relative_rect,
                          manager,
                          container,
@@ -300,12 +302,13 @@ def show(self):
         In addition to the base UIElement.show() - call show() of owned container - panel_container.
         """
         super().show()
-
-        self.panel_container.show()
+        if self.panel_container is not None:
+            self.panel_container.show()
 
     def hide(self):
         """
         In addition to the base UIElement.hide() - call hide() of owned container - panel_container.
         """
-        self.panel_container.hide()
+        if self.panel_container is not None:
+            self.panel_container.hide()
         super().hide()

pygame_gui/elements/ui_scrolling_container.py

@@ -41,7 +41,9 @@ def __init__(self,
                  object_id: Optional[Union[ObjectID, str]] = None,
                  anchors: Optional[Dict[str, Union[str, UIElement]]] = None,
                  visible: int = 1):
-
+        # Need to move some declarations early as they are indirectly referenced via the ui element
+        # constructor
+        self._root_container = None
         super().__init__(relative_rect,
                          manager,
                          container,
@@ -439,7 +441,8 @@ def show(self):
         separately.
         """
         super().show()
-        self._root_container.show()
+        if self._root_container is not None:
+            self._root_container.show()
 
     def hide(self):
         """
@@ -448,5 +451,6 @@ def hide(self):
         it's visibility will propagate to them - there is no need to call their hide() methods
         separately.
         """
-        self._root_container.hide()
+        if self._root_container is not None:
+            self._root_container.hide()
         super().hide()

pygame_gui/elements/ui_selection_list.py

@@ -710,8 +710,8 @@ def show(self):
         there is no need to call their show() methods separately.
         """
         super().show()
-
-        self.list_and_scroll_bar_container.show()
+        if self.list_and_scroll_bar_container is not None:
+            self.list_and_scroll_bar_container.show()
 
     def hide(self):
         """

pygame_gui/elements/ui_vertical_scroll_bar.py

@@ -567,8 +567,8 @@ def show(self):
         propagate and show all the buttons.
         """
         super().show()
-
-        self.button_container.show()
+        if self.button_container is not None:
+            self.button_container.show()
 
     def hide(self):
         """