Added on_resize handler on toga.Window

android/src/toga_android/window.py

@@ -26,6 +26,7 @@ def onGlobalLayout(self):
  """
  native_parent = self.window.native_content.getParent()
  self.window.resize_content(native_parent.getWidth(), native_parent.getHeight())
+ self.window.interface.on_resize()
 
 
 class Window(Container):

changes/2304.feature.rst

@@ -0,0 +1 @@
+Toga Windows now supports calling user functions on resize events.

cocoa/src/toga_cocoa/window.py

@@ -40,6 +40,7 @@ def windowDidResize_(self, notification) -> None:
  if self.interface.content:
  # Set the window to the new size
  self.interface.content.refresh()
+ self.impl.interface.on_resize()
 
  ######################################################################
  # Toolbar delegate methods

core/src/toga/window.py

@@ -90,6 +90,17 @@ def __call__(self, window: Window, **kwargs: Any) -> bool:
  ...
 
 
+class OnResizeHandler(Protocol):
+ def __call__(self, window: Window, **kwargs: Any) -> None:
+ """A handler to invoke when a window resizes.
+
+ :param window: The window instance that resizes.
+ :param kwargs: Ensures compatibility with additional arguments introduced in
+ future ver
+ """
+ ...
+
+
 T = TypeVar("T")
 
 
@@ -126,6 +137,7 @@ def __init__(
  resizable: bool = True,
  closable: bool = True,
  minimizable: bool = True,
+ on_resize: OnResizeHandler | None = None,
  on_close: OnCloseHandler | None = None,
  resizeable=None, # DEPRECATED
  closeable=None, # DEPRECATED
@@ -197,6 +209,7 @@ def __init__(
  self._toolbar = CommandSet(on_change=self._impl.create_toolbar, app=self._app)
 
  self.on_close = on_close
+ self.on_resize = on_resize
 
  def __lt__(self, other) -> bool:
  return self.id < other.id
@@ -468,6 +481,15 @@ def as_image(self, format: type[ImageT] = Image) -> ImageT:
  # Window events
  ######################################################################
 
+ @property
+ def on_resize(self) -> OnResizeHandler:
+ """The handler to invoke when the window resizes."""
+ return self._on_resize
+
+ @on_resize.setter
+ def on_resize(self, handler):
+ self._on_resize = wrapped_handler(self, handler)
+
  @property
  def on_close(self) -> OnCloseHandler:
  """The handler to invoke if the user attempts to close the window."""

core/tests/test_window.py

@@ -354,6 +354,19 @@ def test_as_image(window):
  assert image.size == (318, 346)
 
 
+def test_on_resize(window):
+ assert window.on_resize._raw is None
+
+ on_resize_handler = Mock()
+ window.on_resize = on_resize_handler
+
+ assert window.on_resize._raw == on_resize_handler
+
+ window._impl.simulate_on_resize()
+
+ on_resize_handler.assert_called_once_with(window)
+
+
 def test_screen(window, app):
  """A window can be moved to a different screen."""
  # Cannot actually change window.screen, so just check

dummy/src/toga_dummy/window.py

@@ -110,3 +110,6 @@ def simulate_close(self):
  def get_current_screen(self):
  # `window.screen` will return `Secondary Screen`
  return ScreenImpl(native=("Secondary Screen", (-1366, -768), (1366, 768)))
+
+ def simulate_on_resize(self):
+ self.interface.on_resize()

gtk/src/toga_gtk/window.py

@@ -17,6 +17,7 @@ def __init__(self, interface, title, position, size):
  self.create()
  self.native._impl = self
 
+ self.native.connect("configure-event", self.gtk_configure_event)
  self.native.connect("delete-event", self.gtk_delete_event)
 
  self.native.set_default_size(size[0], size[1])
@@ -57,6 +58,9 @@ def create(self):
  # Native event handlers
  ######################################################################
 
+ def gtk_configure_event(self, widget, data):
+ self.interface.on_resize()
+
  def gtk_delete_event(self, widget, data):
  if self._is_closing:
  should_close = True

iOS/src/toga_iOS/app.py

@@ -50,6 +50,8 @@ def application_didChangeStatusBarOrientation_(
  """This callback is invoked when rotating the device from landscape to portrait
  and vice versa."""
  App.app.interface.main_window.content.refresh()
+ for window in App.app.interface.windows:
+ window.on_resize()
 
 
 class App:

testbed/tests/test_window.py

@@ -520,6 +520,28 @@ async def test_screen(second_window, second_window_probe):
  )
 
 
+async def test_on_resize(main_window, main_window_probe):
+ if toga.platform.current_platform in {"android", "iOS", "web"}:
+ pytest.xfail("Window.on_resize is non functional on current platform.")
+ main_window_on_resize_handler = Mock()
+ main_window.on_resize = main_window_on_resize_handler
+
+ main_window.show()
+ await main_window_probe.wait_for_window("Main window has been shown")
+
+ initial_size = main_window.size
+
+ main_window.size = (200, 150)
+ await main_window_probe.wait_for_window("Main window has been resized")
+ assert main_window.size == (200, 150)
+
+ main_window_on_resize_handler.assert_called_with(main_window)
+
+ main_window.size = initial_size
+ await main_window_probe.wait_for_window("Main window has been resized")
+ assert main_window.size == initial_size
+
+
 async def test_as_image(main_window, main_window_probe):
  """The window can be captured as a screenshot"""
 

textual/src/toga_textual/window.py

@@ -112,6 +112,7 @@ def on_mount(self) -> None:
 
  def on_resize(self, event) -> None:
  self.interface.content.refresh()
+ self.interface.on_resize()
 
 
 class Window:

winforms/src/toga_winforms/window.py

@@ -47,6 +47,7 @@ def __init__(self, interface, title, position, size):
 
  def winforms_Resize(self, sender, event):
  self.resize_content()
+ self.interface.on_resize()
 
  def winforms_FormClosing(self, sender, event):
  # If the app is exiting, or a manual close has been requested, don't get