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): ...

core/src/toga/style/applicator.py

@@ -1,38 +1,42 @@
-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,
+            )
 
     def refresh(self) -> None:
-        # print("RE-EVALUATE LAYOUT", self.widget)
-        self.widget.refresh()
+        # print("RE-EVALUATE LAYOUT", self.node)
+        self.node.refresh()
 
     def set_bounds(self) -> None:
-        # print("  APPLY LAYOUT", self.widget, self.widget.layout)
-        self.widget._impl.set_bounds(
-            self.widget.layout.absolute_content_left,
-            self.widget.layout.absolute_content_top,
-            self.widget.layout.content_width,
-            self.widget.layout.content_height,
+        # print("  APPLY LAYOUT", self.node, self.node.layout)
+        self.node._impl.set_bounds(
+            self.node.layout.absolute_content_left,
+            self.node.layout.absolute_content_top,
+            self.node.layout.content_width,
+            self.node.layout.content_height,
         )
-        for child in self.widget.children:
+        for child in self.node.children:
             child.applicator.set_bounds()
 
     def set_text_alignment(self, alignment: str) -> None:
-        self.widget._impl.set_alignment(alignment)
+        self.node._impl.set_alignment(alignment)
 
     def set_hidden(self, hidden: bool) -> None:
-        self.widget._impl.set_hidden(hidden)
-        for child in self.widget.children:
+        self.node._impl.set_hidden(hidden)
+        for child in self.node.children:
             # If the parent is hidden, then so are all children. However, if the
             # parent is visible, then the child's explicit visibility style is
             # taken into account. This visibility cascades into any
@@ -49,11 +53,11 @@ def set_hidden(self, hidden: bool) -> None:
     def set_font(self, font: object) -> None:
         # Changing the font of a widget can make the widget change size,
         # which in turn means we need to do a re-layout
-        self.widget._impl.set_font(font)
-        self.widget.refresh()
+        self.node._impl.set_font(font)
+        self.node.refresh()
 
     def set_color(self, color: object) -> None:
-        self.widget._impl.set_color(color)
+        self.node._impl.set_color(color)
 
     def set_background_color(self, color: object) -> None:
-        self.widget._impl.set_background_color(color)
+        self.node._impl.set_background_color(color)

core/src/toga/widgets/activityindicator.py

@@ -6,6 +6,8 @@
 
 
 class ActivityIndicator(Widget):
+    _IMPL_NAME = "ActivityIndicator"
+
     def __init__(
         self,
         id: str | None = None,
@@ -22,8 +24,6 @@ def __init__(
         """
         super().__init__(id=id, style=style)
 
-        self._impl = self.factory.ActivityIndicator(interface=self)
-
         if running:
             self.start()
 

core/src/toga/widgets/base.py

@@ -1,7 +1,7 @@
 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
@@ -17,6 +17,8 @@
 
 
 class Widget(Node):
+    _IMPL_NAME = "Widget"
+
     _MIN_WIDTH = 100
     _MIN_HEIGHT = 100
 
@@ -34,16 +36,33 @@ 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._impl = getattr(self.factory, self._IMPL_NAME)(interface=self)
+
+        self.applicator = TogaApplicator()
+
+        ##############################################
+        # Backwards compatibility for Travertino 0.3.0
+        ##############################################
+
+        if not hasattr(self.applicator, "node"):
+            self.applicator.node = self
+            self.style._applicator = self.applicator
+            self.style.reapply()
+        else:  # pragma: no cover
+            pass
+
+        #############################
+        # End backwards compatibility
+        #############################
 
     def __repr__(self) -> str:
         return f"<{self.__class__.__name__}:0x{identifier(self):x}>"

core/src/toga/widgets/box.py

@@ -6,6 +6,8 @@
 
 
 class Box(Widget):
+    _IMPL_NAME = "Box"
+
     _MIN_WIDTH = 0
     _MIN_HEIGHT = 0
 
@@ -24,9 +26,6 @@ def __init__(
         """
         super().__init__(id=id, style=style)
 
-        # Create a platform specific implementation of a Box
-        self._impl = self.factory.Box(interface=self)
-
         # 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

@@ -21,6 +21,8 @@ def __call__(self, widget: Button, /, **kwargs: Any) -> object:
 
 
 class Button(Widget):
+    _IMPL_NAME = "Button"
+
     def __init__(
         self,
         text: str | None = None,
@@ -44,9 +46,6 @@ def __init__(
         """
         super().__init__(id=id, style=style)
 
-        # Create a platform specific implementation of a Button
-        self._impl = self.factory.Button(interface=self)
-
         # 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

@@ -1204,6 +1204,8 @@ def __call__(
 
 
 class Canvas(Widget):
+    _IMPL_NAME = "Canvas"
+
     _MIN_WIDTH = 0
     _MIN_HEIGHT = 0
 
@@ -1241,9 +1243,6 @@ def __init__(
 
         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

@@ -27,6 +27,8 @@ def __call__(self, widget: DateInput, /, **kwargs: Any) -> object:
 
 
 class DateInput(Widget):
+    _IMPL_NAME = "DateInput"
+
     _MIN_WIDTH = 200
 
     def __init__(
@@ -51,9 +53,6 @@ def __init__(
         """
         super().__init__(id=id, style=style)
 
-        # Create a platform specific implementation of a DateInput
-        self._impl = self.factory.DateInput(interface=self)
-
         self.on_change = None
         self.min = min
         self.max = max

core/src/toga/widgets/detailedlist.py

@@ -52,6 +52,8 @@ def __call__(self, widget: DetailedList, /, **kwargs: Any) -> object:
 
 
 class DetailedList(Widget):
+    _IMPL_NAME = "DetailedList"
+
     def __init__(
         self,
         id: str | None = None,
@@ -85,6 +87,15 @@ 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
+
         super().__init__(id=id, style=style)
 
         ######################################################################
@@ -103,17 +114,6 @@ 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

@@ -8,6 +8,8 @@
 
 
 class Divider(Widget):
+    _IMPL_NAME = "Divider"
+
     HORIZONTAL = Direction.HORIZONTAL
     VERTICAL = Direction.VERTICAL
 
@@ -29,8 +31,6 @@ def __init__(
         """
         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

@@ -68,6 +68,8 @@ def rehint_imageview(
 
 
 class ImageView(Widget):
+    _IMPL_NAME = "ImageView"
+
     def __init__(
         self,
         image: ImageContentT | None = None,
@@ -83,10 +85,11 @@ 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)
         # Prime the image attribute
         self._image = None
-        self._impl = self.factory.ImageView(interface=self)
+
+        super().__init__(id=id, style=style)
+
         self.image = image
 
     @property

core/src/toga/widgets/label.py

@@ -4,6 +4,8 @@
 
 
 class Label(Widget):
+    _IMPL_NAME = "Label"
+
     def __init__(
         self,
         text: str,
@@ -19,9 +21,6 @@ def __init__(
         """
         super().__init__(id=id, style=style)
 
-        # Create a platform specific implementation of a Label
-        self._impl = self.factory.Label(interface=self)
-
         self.text = text
 
     def focus(self) -> None:

core/src/toga/widgets/mapview.py

@@ -10,6 +10,8 @@
 
 
 class MapPin:
+    _IMPL_NAME = "MapPin"
+
     def __init__(
         self,
         location: toga.LatLng | tuple[float, float],
@@ -131,6 +133,8 @@ def __call__(self, widget: MapView, /, *, pin: MapPin, **kwargs: Any) -> object:
 
 
 class MapView(Widget):
+    _IMPL_NAME = "MapView"
+
     def __init__(
         self,
         id: str | None = None,
@@ -155,8 +159,6 @@ def __init__(
         """
         super().__init__(id=id, style=style)
 
-        self._impl: Any = self.factory.MapView(interface=self)
-
         self._pins = MapPinSet(self, pins)
 
         if location:

core/src/toga/widgets/multilinetextinput.py

@@ -18,6 +18,8 @@ def __call__(self, widget: MultilineTextInput, /, **kwargs: Any) -> object:
 
 
 class MultilineTextInput(Widget):
+    _IMPL_NAME = "MultilineTextInput"
+
     def __init__(
         self,
         id: str | None = None,
@@ -42,9 +44,6 @@ def __init__(
 
         super().__init__(id=id, style=style)
 
-        # Create a platform specific implementation of a MultilineTextInput
-        self._impl = self.factory.MultilineTextInput(interface=self)
-
         # Set a dummy handler before installing the actual on_change, because we do not want
         # on_change triggered by the initial value being set
         self.on_change = None