diff --git a/changes/3069.feature.rst b/changes/3069.feature.rst
new file mode 100644
index 0000000000..fdb5b8bde9
--- /dev/null
+++ b/changes/3069.feature.rst
@@ -0,0 +1 @@
+The GTK backend now provides an ActivityIndicator widget when ran on GTK4.
diff --git a/core/src/toga/handlers.py b/core/src/toga/handlers.py
index 20b829a1d8..f203159d40 100644
--- a/core/src/toga/handlers.py
+++ b/core/src/toga/handlers.py
@@ -5,6 +5,7 @@
 import sys
 import traceback
 import warnings
+import weakref
 from abc import ABC
 from collections.abc import Awaitable, Callable, Generator
 from typing import TYPE_CHECKING, Any, NoReturn, Protocol, TypeVar, Union
@@ -259,3 +260,25 @@ def __bool__(self, other: object) -> NoReturn:
 
 class PermissionResult(AsyncResult):
     RESULT_TYPE = "permission"
+
+
+class WeakrefCallable:
+    """
+    A wrapper for callable that holds a weak reference to it.
+
+    This can be useful in particular when setting winforms event handlers, to avoid
+    cyclical reference cycles between Python and the .NET CLR that are detected neither
+    by the Python garbage collector nor the C# garbage collector. It is also used
+    for some of the GTK4 event controllers.
+    """
+
+    def __init__(self, function):
+        try:
+            self.ref = weakref.WeakMethod(function)
+        except TypeError:  # pragma: no cover
+            self.ref = weakref.ref(function)
+
+    def __call__(self, *args, **kwargs):
+        function = self.ref()
+        if function:  # pragma: no branch
+            return function(*args, **kwargs)
diff --git a/core/tests/test_handlers.py b/core/tests/test_handlers.py
index f06dd42396..4fecfbbf7b 100644
--- a/core/tests/test_handlers.py
+++ b/core/tests/test_handlers.py
@@ -1,9 +1,16 @@
 import asyncio
+import gc
 from unittest.mock import Mock
 
 import pytest
 
-from toga.handlers import AsyncResult, NativeHandler, simple_handler, wrapped_handler
+from toga.handlers import (
+    AsyncResult,
+    NativeHandler,
+    WeakrefCallable,
+    simple_handler,
+    wrapped_handler,
+)
 
 
 class ExampleAsyncResult(AsyncResult):
@@ -742,3 +749,123 @@ def test_async_exception_cancelled_sync(event_loop):
 
     # The callback wasn't called
     on_result.assert_not_called()
+
+
+def test_weakref_function_call():
+    """Test that WeakrefCallable correctly calls the wrapped function."""
+
+    def test_func(x, y=2):
+        return x + y
+
+    wrc = WeakrefCallable(test_func)
+
+    # Test with positional arguments
+    assert wrc(3) == 5
+
+    # Test with keyword arguments
+    assert wrc(3, y=3) == 6
+
+    # Test with mixed arguments
+    assert wrc(3, 4) == 7
+
+
+def test_weakref_method_call():
+    """Test that WeakrefCallable correctly calls a method."""
+
+    class TestClass:
+        def __init__(self, value):
+            self.value = value
+
+        def method(self, x):
+            return self.value + x
+
+    obj = TestClass(5)
+    wrc = WeakrefCallable(obj.method)
+
+    # Test method call
+    assert wrc(3) == 8
+
+
+def test_weakref_lambda_call():
+    """Test that WeakrefCallable works with lambda functions."""
+    # Store the lambda in a variable to prevent it from being garbage collected
+    lambda_func = lambda x: x * 2  # noqa: E731
+    wrc = WeakrefCallable(lambda_func)
+    assert wrc(5) == 10
+
+
+def test_weakref_gc_function():
+    """Test that function is garbage collected properly."""
+
+    def create_function_wrapper():
+        def temp_func(x):
+            return x * 3
+
+        return WeakrefCallable(temp_func)
+
+    wrc = create_function_wrapper()
+
+    # Force garbage collection
+    gc.collect()
+
+    # The function should be gone
+    assert wrc.ref() is None
+
+
+def test_weakref_gc_method():
+    """Test that method and its object are garbage collected properly."""
+
+    class TempClass:
+        def method(self, x):
+            return x * 4
+
+    def create_method_wrapper():
+        obj = TempClass()
+        return WeakrefCallable(obj.method), obj
+
+    wrc, obj_ref = create_method_wrapper()
+
+    # Object still exists, method should work
+    assert wrc(2) == 8
+
+    # Delete the reference to the object
+    del obj_ref
+
+    # Force garbage collection
+    gc.collect()
+
+    # The method reference should be gone
+    assert wrc.ref() is None
+
+
+def test_weakref_callable_object():
+    """Test that WeakrefCallable works with callable objects."""
+
+    class CallableObject:
+        def __call__(self, x):
+            return x * 5
+
+    obj = CallableObject()
+    wrc = WeakrefCallable(obj)
+
+    # Test call
+    assert wrc(2) == 10
+
+
+def test_weakref_none_result_when_function_gone():
+    """Test that calling the wrapper after the target is collected doesn't error."""
+
+    def create_function_wrapper():
+        def temp_func(x):
+            return x * 3
+
+        return WeakrefCallable(temp_func)
+
+    wrc = create_function_wrapper()
+
+    # Force garbage collection
+    gc.collect()
+
+    # Calling the wrapper should not raise an error
+    result = wrc(10)
+    assert result is None
diff --git a/gtk/src/toga_gtk/container.py b/gtk/src/toga_gtk/container.py
index 8a40077e74..839b4c78ef 100644
--- a/gtk/src/toga_gtk/container.py
+++ b/gtk/src/toga_gtk/container.py
@@ -43,6 +43,7 @@ def do_measure(self, container, orientation, for_size):
                 return container.min_width, container.min_width, -1, -1
             elif orientation == Gtk.Orientation.VERTICAL:
                 return container.min_height, container.min_height, -1, -1
+            return None
 
         def do_allocate(self, container, width, height, baseline):
             """Perform the actual layout for the all widget's children.
@@ -55,18 +56,24 @@ def do_allocate(self, container, width, height, baseline):
             # print(widget._content, f"Container layout {width}x{height} @ 0x0")
 
             if container._content:
-                # Re-evaluate the layout using the  size as the basis for geometry
-                # print("REFRESH LAYOUT", width, height)
-                container._content.interface.style.layout(container)
-
-                # Ensure the minimum content size from the layout is retained
-                container.min_width = container._content.interface.layout.min_width
-                container.min_height = container._content.interface.layout.min_height
+                current_width = container.width
+                current_height = container.height
+                resized = (width, height) != (current_width, current_height)
+
+                if resized or container.needs_redraw:
+                    # print("REFRESH LAYOUT", width, height)
+                    container._content.interface.style.layout(container)
+                    container.min_width = container._content.interface.layout.min_width
+                    container.min_height = (
+                        container._content.interface.layout.min_height
+                    )
 
                 # WARNING! This is the list of children of the *container*, not
                 # the Toga widget. Toga maintains a tree of children; all nodes
                 # in that tree are direct children of the container.
-                child_widget = container.get_last_child()
+
+                # Process each child widget
+                child_widget = container.get_first_child()
                 while child_widget is not None:
                     if child_widget.get_visible():
                         # Set the allocation of the child widget to the computed
@@ -89,7 +96,7 @@ def do_allocate(self, container, width, height, baseline):
                             child_widget.interface.layout.content_height
                         )
                         child_widget.size_allocate(child_widget_allocation, -1)
-                    child_widget = child_widget.get_prev_sibling()
+                    child_widget = child_widget.get_next_sibling()
 
             # The layout has been redrawn
             container.needs_redraw = False
@@ -103,7 +110,7 @@ class TogaContainer(Gtk.Box):
         def __init__(self):
             super().__init__()
 
-            # Because we don’t have access to the existing layout manager, we must
+            # Because we don't have access to the existing layout manager, we must
             # create our custom layout manager class.
             layout_manager = TogaContainerLayoutManager()
             self.set_layout_manager(layout_manager)
@@ -143,7 +150,11 @@ def width(self):
             """
             if self._content is None:
                 return 0
-            return self.compute_bounds(self)[1].get_width()
+
+            if self._dirty_widgets and self.needs_redraw:
+                self.recompute()
+            width = self.get_width()
+            return width
 
         @property
         def height(self):
@@ -153,7 +164,11 @@ def height(self):
             """
             if self._content is None:
                 return 0
-            return self.compute_bounds(self)[1].get_height()
+
+            if self._dirty_widgets and self.needs_redraw:
+                self.recompute()
+            height = self.get_height()
+            return height
 
         @property
         def content(self):
@@ -200,38 +215,6 @@ def recompute(self):
                 self.min_width = self._content.interface.layout.min_width
                 self.min_height = self._content.interface.layout.min_height
 
-        def do_get_preferred_width(self):
-            """Return (recomputing if necessary) the preferred width for the container.
-
-            The preferred size of the container is its minimum size. This
-            preference will be overridden with the layout size when the layout is
-            applied.
-
-            If the container does not yet have content, the minimum width is set to
-            0.
-            """
-            pass
-
-        def do_get_preferred_height(self):
-            """Return (recomputing if necessary) the preferred height for the container.
-
-            The preferred size of the container is its minimum size. This preference
-            will be overridden with the layout size when the layout is applied.
-
-            If the container does not yet have content, the minimum height is set to 0.
-            """
-            pass
-
-        def do_size_allocate(self, allocation):
-            """Perform the actual layout for the widget, and all it's children.
-
-            The container will assume whatever size it has been given by GTK - usually
-            the full space of the window that holds the container. The layout will then
-            be recomputed based on this new available size, and that new geometry will
-            be applied to all child widgets of the container.
-            """
-            pass
-
 else:  # pragma: no-cover-if-gtk4
 
     class TogaContainer(Gtk.Fixed):
diff --git a/gtk/src/toga_gtk/keys.py b/gtk/src/toga_gtk/keys.py
index 6a05c5283e..7f9347bbab 100644
--- a/gtk/src/toga_gtk/keys.py
+++ b/gtk/src/toga_gtk/keys.py
@@ -187,10 +187,10 @@
 }
 
 
-def toga_key(event):
+def toga_key(keyval: int, state: Gdk.ModifierType):
     """Convert a GDK Key Event into a Toga key."""
     try:
-        key = GDK_KEYS[event.keyval]
+        key = GDK_KEYS[keyval]
     except KeyError:  # pragma: no cover
         # Ignore any key event code we can't map. This can happen for weird key
         # combination (ctrl-alt-tux), and if the X server has weird key
@@ -198,15 +198,15 @@ def toga_key(event):
         # need to no-cover this branch.
         return None
 
-    modifiers = set()
+    modifiers: set[Key] = set()
 
-    if event.state & Gdk.ModifierType.SHIFT_MASK:
+    if state & Gdk.ModifierType.SHIFT_MASK:
         modifiers.add(Key.SHIFT)
-    if event.state & Gdk.ModifierType.CONTROL_MASK:
+    if state & Gdk.ModifierType.CONTROL_MASK:
         modifiers.add(Key.MOD_1)
-    if event.state & Gdk.ModifierType.META_MASK:
+    if state & Gdk.ModifierType.META_MASK:
         modifiers.add(Key.MOD_2)
-    if event.state & Gdk.ModifierType.HYPER_MASK:
+    if state & Gdk.ModifierType.HYPER_MASK:
         modifiers.add(Key.MOD_3)
 
     return {"key": key, "modifiers": modifiers}
diff --git a/gtk/src/toga_gtk/widgets/activityindicator.py b/gtk/src/toga_gtk/widgets/activityindicator.py
index 5020a5caae..b3cbb46b6b 100644
--- a/gtk/src/toga_gtk/widgets/activityindicator.py
+++ b/gtk/src/toga_gtk/widgets/activityindicator.py
@@ -7,7 +7,10 @@ def create(self):
         self.native = Gtk.Spinner()
 
     def is_running(self):
-        return self.native.get_property("active")
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            return self.native.get_property("active")
+        else:  # pragma: no-cover-if-gtk3
+            return self.native.get_property("spinning")
 
     def start(self):
         self.native.start()
@@ -23,10 +26,10 @@ def rehint(self):
             #     self.native.get_preferred_width(),
             #     self.native.get_preferred_height(),
             # )
-            width = self.native.get_preferred_width()
-            height = self.native.get_preferred_height()
-
-            self.interface.intrinsic.width = width[0]
-            self.interface.intrinsic.height = height[0]
+            width = self.native.get_preferred_width()[0]
+            height = self.native.get_preferred_height()[0]
         else:  # pragma: no-cover-if-gtk3
-            pass
+            size = self.native.get_preferred_size()[0]
+            width, height = size.width, size.height
+        self.interface.intrinsic.width = width
+        self.interface.intrinsic.height = height
diff --git a/gtk/src/toga_gtk/widgets/textinput.py b/gtk/src/toga_gtk/widgets/textinput.py
index cb87cb97c9..d1f7f60e30 100644
--- a/gtk/src/toga_gtk/widgets/textinput.py
+++ b/gtk/src/toga_gtk/widgets/textinput.py
@@ -20,24 +20,25 @@ def create(self):
             pass
 
     def gtk_on_change(self, *_args):
-        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
-            self.interface._value_changed()
-        else:  # pragma: no-cover-if-gtk3
-            self.interface._value_changed(self.interface)
+        self.interface._value_changed()
 
     def gtk_focus_in_event(self, *_args):
-        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
-            self.interface.on_gain_focus()
-        else:  # pragma: no-cover-if-gtk3
-            self.interface.on_gain_focus(self.interface)
+        self.interface.on_gain_focus()
 
     def gtk_focus_out_event(self, *_args):
         self.interface.on_lose_focus()
 
-    def gtk_key_press_event(self, _, key_val, *_args):
-        key_pressed = toga_key(key_val)
-        if key_pressed and key_pressed["key"] in {Key.ENTER, Key.NUMPAD_ENTER}:
-            self.interface.on_confirm()
+    if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+
+        def gtk_key_press_event(self, _entry, event):
+            key_pressed = toga_key(event.keyval, event.state)
+            if key_pressed and key_pressed["key"] in {Key.ENTER, Key.NUMPAD_ENTER}:
+                self.interface.on_confirm()
+
+    else:  # pragma: no-cover-if-gtk3
+
+        def gtk_key_pressed(self, _controller, keyval, _keycode, state):
+            pass
 
     def get_readonly(self):
         return not self.native.get_property("editable")
diff --git a/gtk/tests_backend/app.py b/gtk/tests_backend/app.py
index f4743b2429..4040caa069 100644
--- a/gtk/tests_backend/app.py
+++ b/gtk/tests_backend/app.py
@@ -237,7 +237,7 @@ def keystroke(self, combination):
         event.is_modifier = state != 0
         event.state = state
 
-        return toga_key(event)
+        return toga_key(event.keyval, event.state)
 
     async def restore_standard_app(self):
         # No special handling needed to restore standard app.
diff --git a/gtk/tests_backend/fonts.py b/gtk/tests_backend/fonts.py
index d09da437f6..f1574cc04d 100644
--- a/gtk/tests_backend/fonts.py
+++ b/gtk/tests_backend/fonts.py
@@ -6,7 +6,7 @@
     SMALL_CAPS,
     SYSTEM_DEFAULT_FONT_SIZE,
 )
-from toga_gtk.libs import Pango
+from toga_gtk.libs import GTK_VERSION, Pango
 
 
 class FontMixin:
@@ -14,34 +14,45 @@ class FontMixin:
     supports_custom_variable_fonts = True
 
     def assert_font_family(self, expected):
-        assert self.font.get_family().split(",")[0] == expected
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            assert self.font.get_family().split(",")[0] == expected
+        else:  # pragma: no-cover-if-gtk3
+            assert self.font.family == expected
 
     def assert_font_size(self, expected):
-        # GTK fonts aren't realized until they appear on a widget.
-        # The actual system default size is determined by the widget theme.
-        # So - if the font size reports as 0, it must be a default system
-        # font size that hasn't been realized yet. Once a font has been realized,
-        # we can't reliably determine what the system font size is, other than
-        # knowing that it must be non-zero. Pick some reasonable bounds instead.
-        #
-        # See also SYSTEM_DEFAULT_FONT_SIZE in toga_gtk/widgets/canvas.py.
-        if self.font.get_size() == 0:
-            assert expected == SYSTEM_DEFAULT_FONT_SIZE
-        elif expected == SYSTEM_DEFAULT_FONT_SIZE:
-            assert 8 < int(self.font.get_size() / Pango.SCALE) < 18
-        else:
-            assert int(self.font.get_size() / Pango.SCALE) == expected
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            # GTK fonts aren't realized until they appear on a widget.
+            # The actual system default size is determined by the widget theme.
+            # So - if the font size reports as 0, it must be a default system
+            # font size that hasn't been realized yet. Once a font has been realized,
+            # we can't reliably determine what the system font size is, other than
+            # knowing that it must be non-zero. Pick some reasonable bounds instead.
+            #
+            # See also SYSTEM_DEFAULT_FONT_SIZE in toga_gtk/widgets/canvas.py.
+            if self.font.get_size() == 0:
+                assert expected == SYSTEM_DEFAULT_FONT_SIZE
+            elif expected == SYSTEM_DEFAULT_FONT_SIZE:
+                assert 8 < int(self.font.get_size() / Pango.SCALE) < 18
+            else:
+                assert int(self.font.get_size() / Pango.SCALE) == expected
+        else:  # pragma: no-cover-if-gtk3
+            assert int(self.font.size) == expected
 
     def assert_font_options(self, weight=NORMAL, style=NORMAL, variant=NORMAL):
-        assert {
-            Pango.Weight.BOLD: BOLD,
-        }.get(self.font.get_weight(), NORMAL) == weight
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            assert {
+                Pango.Weight.BOLD: BOLD,
+            }.get(self.font.get_weight(), NORMAL) == weight
 
-        assert {
-            Pango.Style.ITALIC: ITALIC,
-            Pango.Style.OBLIQUE: OBLIQUE,
-        }.get(self.font.get_style(), NORMAL) == style
+            assert {
+                Pango.Style.ITALIC: ITALIC,
+                Pango.Style.OBLIQUE: OBLIQUE,
+            }.get(self.font.get_style(), NORMAL) == style
 
-        assert {
-            Pango.Variant.SMALL_CAPS: SMALL_CAPS,
-        }.get(self.font.get_variant(), NORMAL) == variant
+            assert {
+                Pango.Variant.SMALL_CAPS: SMALL_CAPS,
+            }.get(self.font.get_variant(), NORMAL) == variant
+        else:  # pragma: no-cover-if-gtk3
+            assert self.font.weight == weight
+            assert self.font.style == style
+            assert self.font.variant == variant
diff --git a/gtk/tests_backend/probe.py b/gtk/tests_backend/probe.py
index ef5b0c49a5..33e932c7e4 100644
--- a/gtk/tests_backend/probe.py
+++ b/gtk/tests_backend/probe.py
@@ -1,4 +1,5 @@
 import asyncio
+import contextlib
 
 import toga
 from toga_gtk.libs import GTK_VERSION, GLib, Gtk
@@ -6,25 +7,51 @@
 
 class BaseProbe:
 
-    def repaint_needed(self):
-        if GTK_VERSION < (4, 0, 0):
-            return Gtk.events_pending()
-        else:
-            return GLib.main_context_default().pending()
-
     async def redraw(self, message=None, delay=0):
         """Request a redraw of the app, waiting until that redraw has completed."""
-        # Force a repaint
-        while self.repaint_needed():
+        if (
+            hasattr(self, "native")
+            and self.native
+            and hasattr(self.native, "queue_draw")
+        ):
+            self.native.queue_draw()
+
+            if frame_clock := self.native.get_frame_clock():
+                handler_id = None
+                with contextlib.suppress(asyncio.TimeoutError):
+                    redraw_complete = asyncio.Future()
+
+                    def on_after_paint(*args):
+                        if not redraw_complete.done():
+                            redraw_complete.set_result(True)
+                        return False
+
+                    handler_id = frame_clock.connect("after-paint", on_after_paint)
+
+                    await asyncio.wait_for(redraw_complete, 0.05)
+                if handler_id is not None:
+                    with contextlib.suppress(SystemError):
+                        frame_clock.disconnect(handler_id)
+
+        # Process events to ensure the UI is fully updated
+        for _ in range(15):
             if GTK_VERSION < (4, 0, 0):
-                Gtk.main_iteration_do(blocking=False)
+                if Gtk.events_pending():
+                    Gtk.main_iteration_do(blocking=False)
+                else:
+                    break
             else:
-                GLib.main_context_default().iteration(may_block=False)
+                context = GLib.main_context_default()
+                if context.pending():
+                    context.iteration(may_block=False)
+                else:
+                    break
+
+        # Always yield to let GTK catch up
+        await asyncio.sleep(0)
 
-        # If we're running slow, wait for a second
         if toga.App.app.run_slow:
             delay = max(1, delay)
-
         if delay:
             print("Waiting for redraw" if message is None else message)
             await asyncio.sleep(delay)
diff --git a/gtk/tests_backend/widgets/base.py b/gtk/tests_backend/widgets/base.py
index 0988c75c84..f170d18e04 100644
--- a/gtk/tests_backend/widgets/base.py
+++ b/gtk/tests_backend/widgets/base.py
@@ -7,7 +7,7 @@
 
 from ..fonts import FontMixin
 from ..probe import BaseProbe
-from .properties import toga_color
+from .properties import toga_color, toga_font
 
 
 class SimpleProbe(BaseProbe, FontMixin):
@@ -22,20 +22,29 @@ def __init__(self, widget):
         # Set the target for keypress events
         self._keypress_target = self.native
 
-        if GTK_VERSION >= (4, 0, 0):
-            pytest.skip("GTK4 only has minimal container support")
-
         # Ensure that the theme isn't using animations for the widget.
-        settings = Gtk.Settings.get_for_screen(self.native.get_screen())
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            settings = Gtk.Settings.get_for_screen(self.native.get_screen())
+        else:  # pragma: no-cover-if-gtk3
+            settings = Gtk.Settings.get_for_display(self.native.get_display())
         settings.set_property("gtk-enable-animations", False)
 
     def assert_container(self, container):
         container_native = container._impl.container
-        for control in container_native.get_children():
-            if control == self.native:
-                break
-        else:
-            raise ValueError(f"cannot find {self.native} in {container_native}")
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            for control in container_native.get_children():
+                if control == self.native:
+                    break
+            else:
+                raise ValueError(f"cannot find {self.native} in {container_native}")
+        else:  # pragma: no-cover-if-gtk3
+            control = container_native.get_last_child()
+            while control is not None:
+                if control == self.native:
+                    break
+                control = control.get_prev_sibling()
+            else:
+                raise ValueError(f"cannot find {self.native} in {container_native}")
 
     def assert_not_contained(self):
         assert self.widget._impl.container is None
@@ -53,13 +62,21 @@ def enabled(self):
 
     @property
     def width(self):
-        return self.native.get_allocation().width
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            return self.native.get_allocation().width
+        else:  # pragma: no-cover-if-gtk3
+            return self.native.get_width()
 
     @property
     def height(self):
-        return self.native.get_allocation().height
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            return self.native.get_allocation().height
+        else:  # pragma: no-cover-if-gtk3
+            return self.native.get_height()
 
     def assert_layout(self, size, position):
+        if GTK_VERSION >= (4, 0, 0):
+            pytest.skip("Accurate layout is not yet supported in GTK4")
         # Widget is contained and in a window.
         assert self.widget._impl.container is not None
         assert self.native.get_parent() is not None
@@ -93,18 +110,43 @@ def shrink_on_resize(self):
 
     @property
     def color(self):
-        sc = self.native.get_style_context()
-        return toga_color(sc.get_property("color", sc.get_state()))
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            sc = self.native.get_style_context()
+            return toga_color(sc.get_property("color", sc.get_state()))
+        else:  # pragma: no-cover-if-gtk3
+            style_provider = self.impl.style_providers.get(("color", id(self.native)))
+            style_value = (
+                style_provider.to_string().split(": ")[1].split(";")[0]
+                if style_provider
+                else None
+            )
+            return toga_color(style_value) if style_value else None
 
     @property
     def background_color(self):
-        sc = self.native.get_style_context()
-        return toga_color(sc.get_property("background-color", sc.get_state()))
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            sc = self.native.get_style_context()
+            return toga_color(sc.get_property("background-color", sc.get_state()))
+        else:  # pragma: no-cover-if-gtk3
+            style_provider = self.impl.style_providers.get(
+                ("background_color", id(self.native))
+            )
+            style_value = (
+                style_provider.to_string().split(": ")[1].split(";")[0]
+                if style_provider
+                else None
+            )
+            return toga_color(style_value) if style_value else None
 
     @property
     def font(self):
-        sc = self.native.get_style_context()
-        return sc.get_property("font", sc.get_state())
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            sc = self.native.get_style_context()
+            return sc.get_property("font", sc.get_state())
+        else:  # pragma: no-cover-if-gtk3
+            style_provider = self.impl.style_providers.get(("font", id(self.native)))
+            font_value = style_provider.to_string() if style_provider else None
+            return toga_font(font_value) if font_value else None
 
     @property
     def is_hidden(self):
@@ -112,9 +154,22 @@ def is_hidden(self):
 
     @property
     def has_focus(self):
-        return self.native.has_focus()
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            return self.native.has_focus()
+        else:  # pragma: no-cover-if-gtk3
+            root = self.native.get_root()
+            focus_widget = root.get_focus()
+            if focus_widget:
+                if focus_widget == self.native:
+                    return self.native.has_focus()
+                else:
+                    return focus_widget.is_ancestor(self.native)
+            else:
+                return False
 
     async def type_character(self, char):
+        if GTK_VERSION >= (4, 0, 0):
+            pytest.skip("GDK KeyPress is not implemented in GTK4")
         # Construct a GDK KeyPress event.
         keyval = getattr(
             Gdk,
diff --git a/gtk/tests_backend/widgets/box.py b/gtk/tests_backend/widgets/box.py
index ccb6fc8f33..47f2bafb8a 100644
--- a/gtk/tests_backend/widgets/box.py
+++ b/gtk/tests_backend/widgets/box.py
@@ -1,7 +1,11 @@
-from toga_gtk.libs import Gtk
+import pytest
+
+from toga_gtk.libs import GTK_VERSION, Gtk
 
 from .base import SimpleProbe
 
 
 class BoxProbe(SimpleProbe):
+    if GTK_VERSION >= (4, 0, 0):
+        pytest.skip("Box is not yet supported with GTK4")
     native_class = Gtk.Box
diff --git a/gtk/tests_backend/widgets/button.py b/gtk/tests_backend/widgets/button.py
index 4d6caa1308..e6a0e42941 100644
--- a/gtk/tests_backend/widgets/button.py
+++ b/gtk/tests_backend/widgets/button.py
@@ -1,13 +1,15 @@
 import pytest
 
 from toga.colors import TRANSPARENT
-from toga_gtk.libs import Gtk
+from toga_gtk.libs import GTK_VERSION, Gtk
 
 from .base import SimpleProbe
 
 
 class ButtonProbe(SimpleProbe):
     native_class = Gtk.Button
+    if GTK_VERSION >= (4, 0, 0):
+        pytest.skip("Button is not yet fully supported in GTK4")
 
     @property
     def text(self):
diff --git a/gtk/tests_backend/widgets/passwordinput.py b/gtk/tests_backend/widgets/passwordinput.py
index 4cf71c1d31..fd34f8c3f7 100644
--- a/gtk/tests_backend/widgets/passwordinput.py
+++ b/gtk/tests_backend/widgets/passwordinput.py
@@ -1,5 +1,11 @@
+import pytest
+
+from toga_gtk.libs import GTK_VERSION
+
 from .textinput import TextInputProbe
 
 
 class PasswordInputProbe(TextInputProbe):
+    if GTK_VERSION >= (4, 0, 0):
+        pytest.skip("Password Input is not yet supported with GTK4")
     pass
diff --git a/gtk/tests_backend/widgets/properties.py b/gtk/tests_backend/widgets/properties.py
index 18470f02be..34fc683e15 100644
--- a/gtk/tests_backend/widgets/properties.py
+++ b/gtk/tests_backend/widgets/properties.py
@@ -1,18 +1,28 @@
 import pytest
 
-from toga.colors import TRANSPARENT, rgba
+from toga.colors import TRANSPARENT, color as parse_color, rgba
+from toga.fonts import Font
 from toga.style.pack import BOTTOM, CENTER, JUSTIFY, LEFT, RIGHT, TOP
-from toga_gtk.libs import Gtk
+from toga_gtk.libs import GTK_VERSION, Gtk
 
 
 def toga_color(color):
     if color:
-        c = rgba(
-            int(color.red * 255),
-            int(color.green * 255),
-            int(color.blue * 255),
-            color.alpha,
-        )
+        if GTK_VERSION < (4, 0, 0):  # pragma: no-cover-if-gtk4
+            c = rgba(
+                int(color.red * 255),
+                int(color.green * 255),
+                int(color.blue * 255),
+                color.alpha,
+            )
+        else:  # pragma: no-cover-if-gtk3
+            color = parse_color(color)
+            c = rgba(
+                int(color.r),
+                int(color.g),
+                int(color.b),
+                color.a,
+            )
 
         # Background color of rgba(0,0,0,0.0) is TRANSPARENT.
         if c.r == 0 and c.g == 0 and c.b == 0 and c.a == 0.0:
@@ -54,3 +64,52 @@ def toga_text_align_from_justification(justify):
         Gtk.Justification.CENTER: CENTER,
         Gtk.Justification.FILL: JUSTIFY,
     }[justify]
+
+
+def toga_font(font: str) -> Font:
+    """
+    Convert CSS font definition to a Toga Font object.
+
+    Args:
+        font (str): CSS font definition string, for example:
+            {
+              font-family: "Helvetica Neue";
+              font-size: 14px;
+              font-style: normal;
+              font-variant: normal;
+              font-weight: 400;
+            }
+
+    Returns:
+        Font: A Toga Font object with the parsed properties
+    """
+    css_dict = {}
+    for line in font.split("\n"):
+        line = line.strip()
+        if ":" in line:
+            property_name, value = line.split(":", 1)
+            property_name = property_name.strip()
+            value = value.strip().rstrip(";")
+            css_dict[property_name] = value
+
+    family_font_value = css_dict.get("font-family", "")
+    size_font_value = css_dict.get("font-size", -1)
+    style_font_value = css_dict.get("font-style", "normal")
+    variant_font_value = css_dict.get("font-variant", "normal")
+    weight_font_value = css_dict.get("font-weight", "normal")
+
+    if variant_font_value == "initial":
+        variant_font_value = "normal"
+
+    if weight_font_value == "400":
+        weight_font_value = "normal"
+    elif weight_font_value == "700":
+        weight_font_value = "bold"
+
+    return Font(
+        family=family_font_value,
+        size=size_font_value,
+        style=style_font_value,
+        variant=variant_font_value,
+        weight=weight_font_value,
+    )
diff --git a/testbed/tests/widgets/conftest.py b/testbed/tests/widgets/conftest.py
index 1c4a37626a..7900f94a92 100644
--- a/testbed/tests/widgets/conftest.py
+++ b/testbed/tests/widgets/conftest.py
@@ -122,27 +122,18 @@ def build_cleanup_test(
     xfail_platforms=(),
 ):
     async def test_cleanup():
-        nonlocal args, kwargs
-
         skip_on_platforms(*skip_platforms)
         xfail_on_platforms(*xfail_platforms, reason="Leaks memory")
 
-        if args is None:
-            args = ()
-
-        if kwargs is None:
-            kwargs = {}
+        local_args = () if args is None else args
+        local_kwargs = {} if kwargs is None else kwargs
 
         with safe_create():
-            widget = widget_constructor(*args, **kwargs)
-
+            widget = widget_constructor(*local_args, **local_kwargs)
         ref = weakref.ref(widget)
-
-        # Args or kwargs may hold a backref to the widget itself, for example if they
-        # are widget content. Ensure that they are deleted before garbage collection.
-        del widget, args, kwargs
+        # Break potential reference cycles
+        del widget, local_args, local_kwargs
         gc.collect()
-
         assert ref() is None
 
     return test_cleanup
diff --git a/testbed/tests/widgets/properties.py b/testbed/tests/widgets/properties.py
index 0615df2dbb..e702e6ced1 100644
--- a/testbed/tests/widgets/properties.py
+++ b/testbed/tests/widgets/properties.py
@@ -87,6 +87,9 @@ async def test_focus(widget, probe, other, other_probe, verify_focus_handlers):
     if verify_focus_handlers:
         on_gain_handler.assert_not_called()
 
+        # Reset the mock so it can be tested again
+        on_lose_handler.reset_mock()
+
     other.focus()
     await probe.redraw("Focus has been lost")
     assert not probe.has_focus
diff --git a/winforms/src/toga_winforms/app.py b/winforms/src/toga_winforms/app.py
index 6967e9f3c4..842040c749 100644
--- a/winforms/src/toga_winforms/app.py
+++ b/winforms/src/toga_winforms/app.py
@@ -11,9 +11,9 @@
 from System.Windows.Threading import Dispatcher
 
 from toga.dialogs import InfoDialog
+from toga.handlers import WeakrefCallable
 
 from .libs.proactor import WinformsProactorEventLoop
-from .libs.wrapper import WeakrefCallable
 from .screens import Screen as ScreenImpl
 
 
diff --git a/winforms/src/toga_winforms/command.py b/winforms/src/toga_winforms/command.py
index 8b888bd521..36d6b8f630 100644
--- a/winforms/src/toga_winforms/command.py
+++ b/winforms/src/toga_winforms/command.py
@@ -3,8 +3,8 @@
 from System.ComponentModel import InvalidEnumArgumentException
 
 from toga import Command as StandardCommand, Group, Key
+from toga.handlers import WeakrefCallable
 from toga_winforms.keys import toga_to_winforms_key, toga_to_winforms_shortcut
-from toga_winforms.libs.wrapper import WeakrefCallable
 
 
 class Command:
diff --git a/winforms/src/toga_winforms/dialogs.py b/winforms/src/toga_winforms/dialogs.py
index 6f090a0268..11ca1fd690 100644
--- a/winforms/src/toga_winforms/dialogs.py
+++ b/winforms/src/toga_winforms/dialogs.py
@@ -9,8 +9,9 @@
 )
 from System.Windows.Forms import DialogResult, MessageBoxButtons, MessageBoxIcon
 
+from toga.handlers import WeakrefCallable
+
 from .libs.user32 import DPI_AWARENESS_CONTEXT_UNAWARE, SetThreadDpiAwarenessContext
-from .libs.wrapper import WeakrefCallable
 
 
 class BaseDialog:
diff --git a/winforms/src/toga_winforms/libs/proactor.py b/winforms/src/toga_winforms/libs/proactor.py
index 276a5f1c4b..dd2fbab44a 100644
--- a/winforms/src/toga_winforms/libs/proactor.py
+++ b/winforms/src/toga_winforms/libs/proactor.py
@@ -8,7 +8,7 @@
 from System import Action
 from System.Threading.Tasks import Task
 
-from .wrapper import WeakrefCallable
+from toga.handlers import WeakrefCallable
 
 
 class WinformsProactorEventLoop(asyncio.ProactorEventLoop):
diff --git a/winforms/src/toga_winforms/libs/wrapper.py b/winforms/src/toga_winforms/libs/wrapper.py
deleted file mode 100644
index 4ad877d3a4..0000000000
--- a/winforms/src/toga_winforms/libs/wrapper.py
+++ /dev/null
@@ -1,22 +0,0 @@
-import weakref
-
-
-class WeakrefCallable:
-    """
-    A wrapper for callable that holds a weak reference to it.
-
-    This can be useful in particular when setting winforms event handlers, to avoid
-    cyclical reference cycles between Python and the .NET CLR that are detected neither
-    by the Python garbage collector nor the C# garbage collector.
-    """
-
-    def __init__(self, function):
-        try:
-            self.ref = weakref.WeakMethod(function)
-        except TypeError:  # pragma: no cover
-            self.ref = weakref.ref(function)
-
-    def __call__(self, *args, **kwargs):
-        function = self.ref()
-        if function:  # pragma: no branch
-            return function(*args, **kwargs)
diff --git a/winforms/src/toga_winforms/statusicons.py b/winforms/src/toga_winforms/statusicons.py
index e581ac69fd..6d360ad204 100644
--- a/winforms/src/toga_winforms/statusicons.py
+++ b/winforms/src/toga_winforms/statusicons.py
@@ -2,8 +2,7 @@
 
 import toga
 from toga.command import Group, Separator
-
-from .libs.wrapper import WeakrefCallable
+from toga.handlers import WeakrefCallable
 
 
 class StatusIcon:
diff --git a/winforms/src/toga_winforms/widgets/button.py b/winforms/src/toga_winforms/widgets/button.py
index ac1ba54b40..fbcc55c589 100644
--- a/winforms/src/toga_winforms/widgets/button.py
+++ b/winforms/src/toga_winforms/widgets/button.py
@@ -4,8 +4,8 @@
 from travertino.size import at_least
 
 from toga.colors import TRANSPARENT
+from toga.handlers import WeakrefCallable
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/canvas.py b/winforms/src/toga_winforms/widgets/canvas.py
index a98a70f53c..ffef73c3ed 100644
--- a/winforms/src/toga_winforms/widgets/canvas.py
+++ b/winforms/src/toga_winforms/widgets/canvas.py
@@ -24,10 +24,10 @@
 
 from toga.colors import TRANSPARENT
 from toga.constants import Baseline, FillRule
+from toga.handlers import WeakrefCallable
 from toga.widgets.canvas import arc_to_bezier, sweepangle
 from toga_winforms.colors import native_color
 
-from ..libs.wrapper import WeakrefCallable
 from .box import Box
 
 
diff --git a/winforms/src/toga_winforms/widgets/dateinput.py b/winforms/src/toga_winforms/widgets/dateinput.py
index d379374bc8..617bbe343d 100644
--- a/winforms/src/toga_winforms/widgets/dateinput.py
+++ b/winforms/src/toga_winforms/widgets/dateinput.py
@@ -4,7 +4,8 @@
 import System.Windows.Forms as WinForms
 from System import DateTime as WinDateTime
 
-from ..libs.wrapper import WeakrefCallable
+from toga.handlers import WeakrefCallable
+
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/mapview.py b/winforms/src/toga_winforms/widgets/mapview.py
index a770c858fe..4e0c24b779 100644
--- a/winforms/src/toga_winforms/widgets/mapview.py
+++ b/winforms/src/toga_winforms/widgets/mapview.py
@@ -8,6 +8,7 @@
 from System.Threading.Tasks import Task, TaskScheduler
 
 import toga
+from toga.handlers import WeakrefCallable
 from toga.types import LatLng
 from toga_winforms.libs.extensions import (
     CoreWebView2CreationProperties,
@@ -15,7 +16,6 @@
     WebView2RuntimeNotFoundException,
 )
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 MAPVIEW_HTML_CONTENT = """<!DOCTYPE html>
diff --git a/winforms/src/toga_winforms/widgets/multilinetextinput.py b/winforms/src/toga_winforms/widgets/multilinetextinput.py
index db12269b6c..2a0f9068d1 100644
--- a/winforms/src/toga_winforms/widgets/multilinetextinput.py
+++ b/winforms/src/toga_winforms/widgets/multilinetextinput.py
@@ -2,10 +2,10 @@
 from System.Drawing import SystemColors
 from travertino.size import at_least
 
+from toga.handlers import WeakrefCallable
 from toga_winforms.colors import native_color
 from toga_winforms.libs.fonts import HorizontalTextAlignment
 
-from ..libs.wrapper import WeakrefCallable
 from .textinput import TextInput
 
 
diff --git a/winforms/src/toga_winforms/widgets/numberinput.py b/winforms/src/toga_winforms/widgets/numberinput.py
index 14cf579403..bc0f685505 100644
--- a/winforms/src/toga_winforms/widgets/numberinput.py
+++ b/winforms/src/toga_winforms/widgets/numberinput.py
@@ -4,10 +4,10 @@
 import System.Windows.Forms as WinForms
 from System import Convert, String
 
+from toga.handlers import WeakrefCallable
 from toga.widgets.numberinput import _clean_decimal
 from toga_winforms.libs.fonts import HorizontalTextAlignment
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/optioncontainer.py b/winforms/src/toga_winforms/widgets/optioncontainer.py
index 2486b0f93b..576af47f80 100644
--- a/winforms/src/toga_winforms/widgets/optioncontainer.py
+++ b/winforms/src/toga_winforms/widgets/optioncontainer.py
@@ -1,7 +1,8 @@
 from System.Windows.Forms import TabControl, TabPage
 
+from toga.handlers import WeakrefCallable
+
 from ..container import Container
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/scrollcontainer.py b/winforms/src/toga_winforms/widgets/scrollcontainer.py
index 415a149484..75a7edbbd1 100644
--- a/winforms/src/toga_winforms/widgets/scrollcontainer.py
+++ b/winforms/src/toga_winforms/widgets/scrollcontainer.py
@@ -4,9 +4,9 @@
 from System.Windows.Forms import Panel, SystemInformation
 from travertino.node import Node
 
+from toga.handlers import WeakrefCallable
 from toga_winforms.container import Container
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 # On Windows, scroll bars usually appear only when the content is larger than the
diff --git a/winforms/src/toga_winforms/widgets/selection.py b/winforms/src/toga_winforms/widgets/selection.py
index d7fc89d2e6..bff2b75ce0 100644
--- a/winforms/src/toga_winforms/widgets/selection.py
+++ b/winforms/src/toga_winforms/widgets/selection.py
@@ -3,7 +3,8 @@
 
 import System.Windows.Forms as WinForms
 
-from ..libs.wrapper import WeakrefCallable
+from toga.handlers import WeakrefCallable
+
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/slider.py b/winforms/src/toga_winforms/widgets/slider.py
index 5051f5860a..34e5e15da3 100644
--- a/winforms/src/toga_winforms/widgets/slider.py
+++ b/winforms/src/toga_winforms/widgets/slider.py
@@ -3,9 +3,9 @@
 import System.Windows.Forms as WinForms
 
 from toga.colors import TRANSPARENT
+from toga.handlers import WeakrefCallable
 from toga.widgets.slider import IntSliderImpl
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 # Implementation notes
diff --git a/winforms/src/toga_winforms/widgets/splitcontainer.py b/winforms/src/toga_winforms/widgets/splitcontainer.py
index 812ef3aebe..d666f4a19b 100644
--- a/winforms/src/toga_winforms/widgets/splitcontainer.py
+++ b/winforms/src/toga_winforms/widgets/splitcontainer.py
@@ -5,9 +5,9 @@
 )
 
 from toga.constants import Direction
+from toga.handlers import WeakrefCallable
 
 from ..container import Container
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/switch.py b/winforms/src/toga_winforms/widgets/switch.py
index ea01598194..21a382a8e2 100644
--- a/winforms/src/toga_winforms/widgets/switch.py
+++ b/winforms/src/toga_winforms/widgets/switch.py
@@ -4,8 +4,8 @@
 from travertino.size import at_least
 
 from toga.colors import TRANSPARENT
+from toga.handlers import WeakrefCallable
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/table.py b/winforms/src/toga_winforms/widgets/table.py
index b6d2014cdd..726658d75d 100644
--- a/winforms/src/toga_winforms/widgets/table.py
+++ b/winforms/src/toga_winforms/widgets/table.py
@@ -3,8 +3,8 @@
 import System.Windows.Forms as WinForms
 
 import toga
+from toga.handlers import WeakrefCallable
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/textinput.py b/winforms/src/toga_winforms/widgets/textinput.py
index 6a48312668..351f395dc8 100644
--- a/winforms/src/toga_winforms/widgets/textinput.py
+++ b/winforms/src/toga_winforms/widgets/textinput.py
@@ -4,10 +4,10 @@
 
 import System.Windows.Forms as WinForms
 
+from toga.handlers import WeakrefCallable
 from toga_winforms.colors import native_color
 from toga_winforms.libs.fonts import HorizontalTextAlignment
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/timeinput.py b/winforms/src/toga_winforms/widgets/timeinput.py
index 543d988c0c..bb3a6b3509 100644
--- a/winforms/src/toga_winforms/widgets/timeinput.py
+++ b/winforms/src/toga_winforms/widgets/timeinput.py
@@ -4,7 +4,8 @@
 import System.Windows.Forms as WinForms
 from System import DateTime as WinDateTime
 
-from ..libs.wrapper import WeakrefCallable
+from toga.handlers import WeakrefCallable
+
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/widgets/webview.py b/winforms/src/toga_winforms/widgets/webview.py
index 71d71698d2..d273dee385 100644
--- a/winforms/src/toga_winforms/widgets/webview.py
+++ b/winforms/src/toga_winforms/widgets/webview.py
@@ -13,6 +13,7 @@
 from System.Threading.Tasks import Task, TaskScheduler
 
 import toga
+from toga.handlers import WeakrefCallable
 from toga.widgets.webview import CookiesResult, JavaScriptResult
 from toga_winforms.libs.extensions import (
     CoreWebView2Cookie,
@@ -21,7 +22,6 @@
     WebView2RuntimeNotFoundException,
 )
 
-from ..libs.wrapper import WeakrefCallable
 from .base import Widget
 
 
diff --git a/winforms/src/toga_winforms/window.py b/winforms/src/toga_winforms/window.py
index c97a7cce78..45833d5fe3 100644
--- a/winforms/src/toga_winforms/window.py
+++ b/winforms/src/toga_winforms/window.py
@@ -10,11 +10,11 @@
 from toga import App
 from toga.command import Separator
 from toga.constants import WindowState
+from toga.handlers import WeakrefCallable
 from toga.types import Position, Size
 
 from .container import Container
 from .fonts import DEFAULT_FONT
-from .libs.wrapper import WeakrefCallable
 from .screens import Screen as ScreenImpl
 from .widgets.base import Scalable