Implement window refresh lock

changes/2438.feature.rst

@@ -0,0 +1 @@
+Windows now have a refresh lock to stop refreshing window layout happening after every add()

core/src/toga/widgets/base.py

@@ -242,6 +242,9 @@ def enabled(self, value: bool) -> None:
  self._impl.set_enabled(bool(value))
 
  def refresh(self) -> None:
+ if self.window is not None and self.window.locked:
+ return
+
  self._impl.refresh()
 
  # Refresh the layout

core/src/toga/window.py

@@ -28,6 +28,8 @@
  from toga.screens import Screen
  from toga.widgets.base import Widget
 
+from contextlib import contextmanager
+
 
 class FilteredWidgetRegistry:
  # A class that exposes a mapping lookup interface, filtered to widgets from a single
@@ -174,6 +176,7 @@ def __init__(
  self._content = None
  self._is_full_screen = False
  self._closed = False
+ self._locked = False
 
  self._resizable = resizable
  self._closable = closable
@@ -346,6 +349,29 @@ def size(self, size: tuple[int, int]) -> None:
  if self.content:
  self.content.refresh()
 
+ @property
+ def locked(self) -> bool:
+ """Is the window locked from refreshes?"""
+ return self._locked
+
+ @locked.setter
+ def locked(self, locked: bool) -> None:
+ """Lock or unlock window refresh.
+ When window is unlocked, refresh the content
+ """
+ self._locked = locked
+ if not locked:
+ self.content.refresh()
+
+ @contextmanager
+ def refresh_lock(self, *args, **kwargs):
+ """Obtain a refresh lock on the window. Unlocks
+ automatically when context manager leaves scope.
+ """
+ self.locked = True
+ yield
+ self.locked = False
+
  ######################################################################
  # Window position
  ######################################################################

core/tests/test_window.py

@@ -169,6 +169,42 @@ def test_change_content(window, app):
  assert content1.window is None
 
 
+def test_change_content_locked(window, app):
+ """The refresh of a window can be locked"""
+ with window.refresh_lock():
+ assert window.content is None
+ assert window.app == app
+
+ # Set the content of the window
+ content1 = toga.Box()
+ window.content = content1
+
+ # The content has been assigned and not (yet) refreshed
+ assert content1.app == app
+ assert content1.window == window
+ assert_action_performed_with(window, "set content", widget=content1._impl)
+ assert_action_not_performed(content1, "refresh")
+
+ # Set the content of the window to something new
+ content2 = toga.Box()
+ window.content = content2
+
+ # The content has been assigned and not (yet) refreshed
+ assert content2.app == app
+ assert content2.window == window
+ assert_action_performed_with(window, "set content", widget=content2._impl)
+ assert_action_not_performed(content2, "refresh")
+
+ # The original content has been removed
+ assert content1.window is None
+
+ # Action refresh must not have been performed on content1
+ assert_action_not_performed(content1, "refresh")
+
+ # Action refresh must have been performed on content2
+ assert_action_performed(content2, "refresh")
+
+
 def test_set_position(window):
  """The position of the window can be set."""
  window.position = (123, 456)