Gui/fixes (#2795)

* Fix UIManager to correctly handle size hint of (0, 0)
* Refactor UIScrollArea to allow multiple children and detect UIScrollArea in UIDropdown
* Update CHANGELOG.md to reflect UIScrollArea enhancements and UIDropdown positioning fix

Author: eruvanos

CHANGELOG.md

@@ -8,6 +8,10 @@ Arcade [PyPi Release History](https://pypi.org/project/arcade/#history) page.
 - Upgraded Pillow to 12.0.0 for Python 3.14 support.
 - Adds a new `arcade.NoAracdeWindowError` exception type. This is raised when certain window operations are performed and there is no valid Arcade window found. Previously where this error would be raised, we raised a standard `RuntimeError`, this made it harder to properly catch and act accordingly. This new exception subclasses `RuntimeError`, so you can still catch this error the same way as before. The `arcade.get_window()` function will now raise this if there is no window.
 - Along with the new exception type, is a new `arcade.windows_exists()` function which will return True or False based on if there is currently an active window.
+- GUI
+  - `UIManager` did not apply size hint of (0,0). Mainly an issue with `UIBoxLayout`.
+  - Allow multiple children in `UIScrollArea`.
+  - Fix `UIDropdown Overlay` positioning within a `UIScrollArea`.
 
 ## 3.3.3
 

arcade/gui/experimental/scroll_area.py

@@ -239,9 +239,6 @@ def __init__(
 
     def add(self, child: W, **kwargs) -> W:
         """Add a child to the widget."""
-        if self._children:
-            raise ValueError("UIScrollArea can only have one child")
-
         super().add(child, **kwargs)
         self.trigger_full_render()
 

arcade/gui/ui_manager.py

@@ -246,8 +246,8 @@ def _do_layout(self):
                 # actual layout
                 if child.size_hint:
                     sh_x, sh_y = child.size_hint
-                    nw = surface_width * sh_x if sh_x else None
-                    nh = surface_height * sh_y if sh_y else None
+                    nw = surface_width * sh_x if sh_x is not None else None
+                    nh = surface_height * sh_y if sh_y is not None else None
                     child.rect = child.rect.resize(nw, nh, anchor=AnchorPoint.BOTTOM_LEFT)
 
                 if child.size_hint_min:

arcade/gui/widgets/dropdown.py

@@ -6,6 +6,7 @@
 from arcade import uicolor
 from arcade.gui import UIEvent, UIMousePressEvent
 from arcade.gui.events import UIControllerButtonPressEvent, UIOnChangeEvent, UIOnClickEvent
+from arcade.gui.experimental import UIScrollArea
 from arcade.gui.experimental.focus import UIFocusMixin
 from arcade.gui.ui_manager import UIManager
 from arcade.gui.widgets import UILayout, UIWidget
@@ -21,7 +22,7 @@ class _UIDropdownOverlay(UIFocusMixin, UIBoxLayout):
 
     # TODO move also options logic to this class
 
-    def show(self, manager: UIManager):
+    def show(self, manager: UIManager | UIScrollArea):
         manager.add(self, layer=UIManager.OVERLAY_LAYER)
 
     def hide(self):
@@ -197,11 +198,19 @@ def _update_options(self):
         self._overlay.detect_focusable_widgets()
 
     def _show_overlay(self):
-        manager = self.get_ui_manager()
-        if manager is None:
-            raise Exception("UIDropdown could not find UIManager in its parents.")
-
-        self._overlay.show(manager)
+        # traverse parents until UIManager or UIScrollArea is found
+        parent = self.parent
+        while parent is not None:
+            if isinstance(parent, UIManager):
+                break
+            if isinstance(parent, UIScrollArea):
+                break
+            parent = parent.parent
+
+        if parent is None:
+            raise Exception("UIDropdown could not find a valid parent for the overlay.")
+
+        self._overlay.show(parent)
 
     def _on_button_click(self, _: UIOnClickEvent):
         self._show_overlay()

tests/unit/gui/test_uimanager_layouting.py

@@ -25,16 +25,21 @@ def test_supports_size_hint(window):
     widget3 = UIDummy()
     widget3.size_hint = (1, None)
 
+    widget4 = UIDummy()
+    widget4.size_hint = (0, 0)
+
     manager.add(widget1)
     manager.add(widget2)
     manager.add(widget3)
+    manager.add(widget4)
 
     with sized(window, 200, 300):
         manager.draw()
 
     assert widget1.size == Vec2(200, 300)
     assert widget2.size == Vec2(100, 75)
     assert widget3.size == Vec2(200, 100)
+    assert widget4.size == Vec2(0, 0)
 
 
 def test_supports_size_hint_min(window):