Restructured widget initialization order

changes/2942.misc.rst

@@ -0,0 +1 @@
+The initialization process for widgets has been internally restructured to avoid unnecessary style reapplications.

cocoa/src/toga_cocoa/widgets/base.py

@@ -9,12 +9,10 @@ class Widget:
     def __init__(self, interface):
         super().__init__()
         self.interface = interface
-        self.interface._impl = self
         self._container = None
         self.constraints = None
         self.native = None
         self.create()
-        self.interface.style.reapply()
 
     @abstractmethod
     def create(self): ...

cocoa/src/toga_cocoa/widgets/button.py

@@ -32,7 +32,7 @@ def create(self):
         self._icon = None
 
         self.native.buttonType = NSMomentaryPushInButton
-        self._set_button_style()
+        # self._set_button_style()
 
         self.native.target = self.native
         self.native.action = SEL("onPress:")

core/src/toga/style/applicator.py

@@ -1,16 +1,38 @@
 from __future__ import annotations
 
+import warnings
 from typing import TYPE_CHECKING
 
 if TYPE_CHECKING:
     from toga.widgets.base import Widget
 
+# Make sure deprecation warnings are shown by default
+warnings.filterwarnings("default", category=DeprecationWarning)
+
 
 class TogaApplicator:
     """Apply styles to a Toga widget."""
 
-    def __init__(self, widget: Widget):
-        self.widget = widget
+    def __init__(self, widget: None = None):
+        if widget is not None:
+            warnings.warn(
+                "Widget parameter is deprecated. Applicator will be given a reference "
+                "to its widget when it is assigned as that widget's applicator.",
+                DeprecationWarning,
+                stacklevel=2,
+            )
+
+    @property
+    def widget(self) -> Widget:
+        """The widget to which this applicator is assigned.
+
+        Syntactic sugar over the node attribute set by Travertino.
+        """
+        return self.node
+
+    @widget.setter
+    def widget(self, widget: Widget):
+        self.node = widget
 
     def refresh(self) -> None:
         # print("RE-EVALUATE LAYOUT", self.widget)

core/src/toga/widgets/activityindicator.py

@@ -2,6 +2,8 @@
 
 from typing import Literal
 
+from toga.platform import get_platform_factory
+
 from .base import StyleT, Widget
 
 
@@ -20,10 +22,11 @@ def __init__(
         :param running: Describes whether the indicator is running at the
             time it is created.
         """
-        super().__init__(id=id, style=style)
-
+        self.factory = get_platform_factory()
         self._impl = self.factory.ActivityIndicator(interface=self)
 
+        super().__init__(id=id, style=style)
+
         if running:
             self.start()
 

core/src/toga/widgets/base.py

@@ -1,12 +1,11 @@
 from __future__ import annotations
 
 from builtins import id as identifier
-from typing import TYPE_CHECKING, Any, TypeVar
+from typing import TYPE_CHECKING, TypeVar
 
 from travertino.declaration import BaseStyle
 from travertino.node import Node
 
-from toga.platform import get_platform_factory
 from toga.style import Pack, TogaApplicator
 
 if TYPE_CHECKING:
@@ -17,6 +16,8 @@
 
 
 class Widget(Node):
+    _IMPL_NAME = "Widget"
+
     _MIN_WIDTH = 100
     _MIN_HEIGHT = 100
 
@@ -34,16 +35,36 @@ def __init__(
             will be applied to the widget.
         """
         super().__init__(
-            style=style if style else Pack(),
-            applicator=TogaApplicator(self),
+            style=style if style is not None else Pack(),
+            applicator=None,
         )
 
         self._id = str(id if id else identifier(self))
         self._window: Window | None = None
         self._app: App | None = None
-        self._impl: Any = None
 
-        self.factory = get_platform_factory()
+        self.applicator = TogaApplicator()
+
+        ##############################################
+        # Backwards compatibility for Travertino 0.3.0
+        ##############################################
+
+        # The below if block will execute when using Travertino 0.3.0. For future
+        # versions of Travertino, these assignments (and the reapply) will already have
+        # been handled "automatically" by assigning the applicator above; in that case,
+        # we want to avoid doing a second, redundant style reapplication.
+
+        # This whole section can be removed as soon as there's a newer version of
+        # Travertino to set as Toga's minimum requirement.
+
+        if not hasattr(self.applicator, "node"):  # pragma: no cover
+            self.applicator.node = self
+            self.style._applicator = self.applicator
+            self.style.reapply()
+
+        #############################
+        # End backwards compatibility
+        #############################
 
     def __repr__(self) -> str:
         return f"<{self.__class__.__name__}:0x{identifier(self):x}>"

core/src/toga/widgets/box.py

@@ -2,6 +2,8 @@
 
 from collections.abc import Iterable
 
+from toga.platform import get_platform_factory
+
 from .base import StyleT, Widget
 
 
@@ -22,11 +24,11 @@ def __init__(
             will be applied to the widget.
         :param children: An optional list of children for to add to the Box.
         """
-        super().__init__(id=id, style=style)
-
-        # Create a platform specific implementation of a Box
+        self.factory = get_platform_factory()
         self._impl = self.factory.Box(interface=self)
 
+        super().__init__(id=id, style=style)
+
         # Children need to be added *after* the impl has been created.
         self._children: list[Widget] = []
         if children is not None:

core/src/toga/widgets/button.py

@@ -4,6 +4,7 @@
 
 import toga
 from toga.handlers import wrapped_handler
+from toga.platform import get_platform_factory
 
 from .base import StyleT, Widget
 
@@ -42,11 +43,11 @@ def __init__(
         :param enabled: Is the button enabled (i.e., can it be pressed?). Optional; by
             default, buttons are created in an enabled state.
         """
-        super().__init__(id=id, style=style)
-
-        # Create a platform specific implementation of a Button
+        self.factory = get_platform_factory()
         self._impl = self.factory.Button(interface=self)
 
+        super().__init__(id=id, style=style)
+
         # Set a dummy handler before installing the actual on_press, because we do not want
         # on_press triggered by the initial value being set
         self.on_press = None

core/src/toga/widgets/canvas.py

@@ -25,6 +25,7 @@
     Font,
 )
 from toga.handlers import wrapped_handler
+from toga.platform import get_platform_factory
 
 from .base import StyleT, Widget
 
@@ -1236,14 +1237,13 @@ def __init__(
         :param on_alt_release: Initial :any:`on_alt_release` handler.
         :param on_alt_drag: Initial :any:`on_alt_drag` handler.
         """
+        self.factory = get_platform_factory()
+        self._impl = self.factory.Canvas(interface=self)
 
         super().__init__(id=id, style=style)
 
         self._context = Context(canvas=self)
 
-        # Create a platform specific implementation of Canvas
-        self._impl = self.factory.Canvas(interface=self)
-
         # Set all the properties
         self.on_resize = on_resize
         self.on_press = on_press

core/src/toga/widgets/dateinput.py

@@ -6,6 +6,7 @@
 
 import toga
 from toga.handlers import wrapped_handler
+from toga.platform import get_platform_factory
 
 from .base import StyleT, Widget
 
@@ -27,6 +28,8 @@ def __call__(self, widget: DateInput, /, **kwargs: Any) -> object:
 
 
 class DateInput(Widget):
+    _IMPL_NAME = "DateInput"
+
     _MIN_WIDTH = 200
 
     def __init__(
@@ -49,11 +52,11 @@ def __init__(
         :param max: The latest date (inclusive) that can be selected.
         :param on_change: A handler that will be invoked when the value changes.
         """
-        super().__init__(id=id, style=style)
-
-        # Create a platform specific implementation of a DateInput
+        self.factory = get_platform_factory()
         self._impl = self.factory.DateInput(interface=self)
 
+        super().__init__(id=id, style=style)
+
         self.on_change = None
         self.min = min
         self.max = max

core/src/toga/widgets/detailedlist.py

@@ -6,6 +6,7 @@
 
 import toga
 from toga.handlers import wrapped_handler
+from toga.platform import get_platform_factory
 from toga.sources import ListSource, Row, Source
 
 from .base import StyleT, Widget
@@ -85,6 +86,18 @@ def __init__(
         :param on_refresh: Initial :any:`on_refresh` handler.
         :param on_delete: **DEPRECATED**; use ``on_primary_action``.
         """
+        # Prime the attributes and handlers that need to exist when the widget is created.
+        self._accessors = accessors
+        self._missing_value = missing_value
+        self._primary_action = primary_action
+        self._secondary_action = secondary_action
+        self.on_select = None
+
+        self._data: SourceT | ListSource = None
+
+        self.factory = get_platform_factory()
+        self._impl = self.factory.DetailedList(interface=self)
+
         super().__init__(id=id, style=style)
 
         ######################################################################
@@ -103,17 +116,6 @@ def __init__(
         # End backwards compatibility.
         ######################################################################
 
-        # Prime the attributes and handlers that need to exist when the widget is created.
-        self._accessors = accessors
-        self._missing_value = missing_value
-        self._primary_action = primary_action
-        self._secondary_action = secondary_action
-        self.on_select = None
-
-        self._data: SourceT | ListSource = None
-
-        self._impl = self.factory.DetailedList(interface=self)
-
         self.data = data
         self.on_primary_action = on_primary_action
         self.on_secondary_action = on_secondary_action

core/src/toga/widgets/divider.py

@@ -3,6 +3,7 @@
 from typing import Literal
 
 from toga.constants import Direction
+from toga.platform import get_platform_factory
 
 from .base import StyleT, Widget
 
@@ -27,10 +28,11 @@ def __init__(
             :attr:`~toga.constants.Direction.VERTICAL`; defaults to
             :attr:`~toga.constants.Direction.HORIZONTAL`
         """
+        self.factory = get_platform_factory()
+        self._impl = self.factory.Divider(interface=self)
+
         super().__init__(id=id, style=style)
 
-        # Create a platform specific implementation of a Divider
-        self._impl = self.factory.Divider(interface=self)
         self.direction = direction
 
     @property

core/src/toga/widgets/imageview.py

@@ -5,6 +5,7 @@
 from travertino.size import at_least
 
 import toga
+from toga.platform import get_platform_factory
 from toga.style.pack import NONE
 from toga.widgets.base import StyleT, Widget
 
@@ -83,10 +84,14 @@ def __init__(
         :param style: A style object. If no style is provided, a default style will be
             applied to the widget.
         """
-        super().__init__(id=id, style=style)
         # Prime the image attribute
         self._image = None
+
+        self.factory = get_platform_factory()
         self._impl = self.factory.ImageView(interface=self)
+
+        super().__init__(id=id, style=style)
+
         self.image = image
 
     @property

core/src/toga/widgets/label.py

@@ -1,5 +1,7 @@
 from __future__ import annotations
 
+from toga.platform import get_platform_factory
+
 from .base import StyleT, Widget
 
 
@@ -17,11 +19,11 @@ def __init__(
         :param style: A style object. If no style is provided, a default style
             will be applied to the widget.
         """
-        super().__init__(id=id, style=style)
-
-        # Create a platform specific implementation of a Label
+        self.factory = get_platform_factory()
         self._impl = self.factory.Label(interface=self)
 
+        super().__init__(id=id, style=style)
+
         self.text = text
 
     def focus(self) -> None:

core/src/toga/widgets/mapview.py

@@ -5,11 +5,14 @@
 
 import toga
 from toga.handlers import wrapped_handler
+from toga.platform import get_platform_factory
 
 from .base import StyleT, Widget
 
 
 class MapPin:
+    _IMPL_NAME = "MapPin"
+
     def __init__(
         self,
         location: toga.LatLng | tuple[float, float],
@@ -153,9 +156,10 @@ def __init__(
         :param on_select: A handler that will be invoked when the user selects a map
             pin.
         """
-        super().__init__(id=id, style=style)
+        self.factory = get_platform_factory()
+        self._impl = self.factory.MapView(interface=self)
 
-        self._impl: Any = self.factory.MapView(interface=self)
+        super().__init__(id=id, style=style)
 
         self._pins = MapPinSet(self, pins)