Resolve remaining iOS widget memory leaks.

changes/2849.bugfix.rst

@@ -0,0 +1 @@
+Widgets on the iOS backend no longer leak memory when destroyed.

iOS/src/toga_iOS/constraints.py

@@ -34,10 +34,15 @@ def __del__(self):  # pragma: nocover
     def _remove_constraints(self):
         if self.container:
             # print(f"Remove constraints for {self.widget} in {self.container}")
-            self.container.native.removeConstraint(self.width_constraint)
-            self.container.native.removeConstraint(self.height_constraint)
-            self.container.native.removeConstraint(self.left_constraint)
-            self.container.native.removeConstraint(self.top_constraint)
+            # Due to the unpredictability of garbage collection, it's possible for
+            # the native object of the window's container to be deleted on the ObjC
+            # side before the constraints for the window have been removed. Protect
+            # against this possibility.
+            if self.container.native:
+                self.container.native.removeConstraint(self.width_constraint)
+                self.container.native.removeConstraint(self.height_constraint)
+                self.container.native.removeConstraint(self.left_constraint)
+                self.container.native.removeConstraint(self.top_constraint)
 
     @property
     def container(self):

iOS/src/toga_iOS/container.py

@@ -72,6 +72,11 @@ def __init__(self, content=None, layout_native=None, on_refresh=None):
 
         self.layout_native = self.native if layout_native is None else layout_native
 
+    def __del__(self):
+        # Mark the contained native object as explicitly None so that the
+        # constraints know the object has been deleted.
+        self.native = None
+
     @property
     def width(self):
         return self.layout_native.bounds.size.width

iOS/src/toga_iOS/widgets/box.py

@@ -12,10 +12,7 @@ class TogaView(UIView):
 
 class Box(Widget):
     def create(self):
-        # This should be a TogaView - but making it a TogaView causes segfaults when
-        # content is added and removed from containers like OptionContainer and
-        # ScrollContainer.
-        self.native = UIView.alloc().init()
+        self.native = TogaView.alloc().init()
         self.native.interface = self.interface
         self.native.impl = self
 

iOS/src/toga_iOS/widgets/selection.py

@@ -12,9 +12,15 @@
 from toga_iOS.widgets.base import Widget
 
 
+class TogaBaseTextField(UITextField):
+    interface = objc_property(object, weak=True)
+    impl = objc_property(object, weak=True)
+
+
 class TogaPickerView(UIPickerView):
     interface = objc_property(object, weak=True)
     impl = objc_property(object, weak=True)
+    native = objc_property(object, weak=True)
 
     @objc_method
     def numberOfComponentsInPickerView_(self, pickerView) -> int:
@@ -53,7 +59,7 @@ def pickerView_didSelectRow_inComponent_(
 
 class Selection(Widget):
     def create(self):
-        self.native = UITextField.alloc().init()
+        self.native = TogaBaseTextField.alloc().init()
         self.native.interface = self.interface
         self.native.impl = self
         self.native.tintColor = UIColor.clearColor

testbed/tests/widgets/test_box.py

@@ -18,4 +18,4 @@ async def widget():
     return toga.Box(style=Pack(width=100, height=200))
 
 
-test_cleanup = build_cleanup_test(toga.Box, xfail_platforms=("iOS",))
+test_cleanup = build_cleanup_test(toga.Box)

testbed/tests/widgets/test_imageview.py

@@ -19,7 +19,7 @@ async def widget():
 
 
 test_cleanup = build_cleanup_test(
-    toga.ImageView, kwargs={"image": "resources/sample.png"}, xfail_platforms=("iOS",)
+    toga.ImageView, kwargs={"image": "resources/sample.png"}
 )
 
 

testbed/tests/widgets/test_optioncontainer.py

@@ -76,7 +76,7 @@ async def widget(content1, content2, content3, on_select_handler):
     # Pass a function here to prevent init of toga.Box() in a different thread than
     # toga.OptionContainer. This would raise a runtime error on Windows.
     lambda: toga.OptionContainer(content=[("Tab 1", toga.Box())]),
-    xfail_platforms=("android", "iOS", "linux"),
+    xfail_platforms=("android", "linux"),
 )
 
 

testbed/tests/widgets/test_scrollcontainer.py

@@ -77,7 +77,7 @@ async def widget(content, on_scroll):
     # Pass a function here to prevent init of toga.Box() in a different thread than
     # toga.ScrollContainer. This would raise a runtime error on Windows.
     lambda: toga.ScrollContainer(content=toga.Box()),
-    xfail_platforms=("android", "iOS", "linux"),
+    xfail_platforms=("android", "linux"),
 )
 
 

testbed/tests/widgets/test_selection.py

@@ -55,7 +55,7 @@ def verify_vertical_text_align():
 test_cleanup = build_cleanup_test(
     toga.Selection,
     kwargs={"items": ["first", "second", "third"]},
-    xfail_platforms=("android", "iOS", "windows"),
+    xfail_platforms=("android", "windows"),
 )