FocusNode and FocusManager should dispatch creation in constructor. (#133352)

packages/flutter/lib/src/material/drawer.dart

@@ -471,6 +471,7 @@ class DrawerControllerState extends State<DrawerController> with SingleTickerPro
   void dispose() {
     _historyEntry?.remove();
     _controller.dispose();
+    _focusScopeNode.dispose();
     super.dispose();
   }
 

packages/flutter/lib/src/widgets/focus_manager.dart

@@ -437,6 +437,10 @@ class FocusNode with DiagnosticableTreeMixin, ChangeNotifier {
         _descendantsAreTraversable = descendantsAreTraversable {
     // Set it via the setter so that it does nothing on release builds.
     this.debugLabel = debugLabel;
+
+    if (kFlutterMemoryAllocationsEnabled) {
+      maybeDispatchObjectCreation();
+    }
   }
 
   /// If true, tells the focus traversal policy to skip over this node for
@@ -1463,6 +1467,9 @@ class FocusManager with DiagnosticableTreeMixin, ChangeNotifier {
   /// handlers, callers must call [registerGlobalHandlers]. See the
   /// documentation in that method for caveats to watch out for.
   FocusManager() {
+    if (kFlutterMemoryAllocationsEnabled) {
+      maybeDispatchObjectCreation();
+    }
     rootScope._manager = this;
   }
 

packages/flutter/test/widgets/focus_manager_test.dart

@@ -1609,6 +1609,41 @@ void main() {
     tester.binding.focusManager.removeListener(handleFocusChange);
   });
 
+  test('$FocusManager dispatches object creation in constructor', () {
+    final List<ObjectEvent> events = <ObjectEvent>[];
+    void listener(ObjectEvent event) {
+      if (event.object.runtimeType == FocusManager) {
+        events.add(event);
+      }
+    }
+    MemoryAllocations.instance.addListener(listener);
+
+    final FocusManager focusManager = FocusManager();
+
+    expect(events, hasLength(1));
+
+    focusManager.dispose();
+
+    MemoryAllocations.instance.removeListener(listener);
+  });
+
+  test('$FocusNode dispatches object creation in constructor', () {
+    final List<ObjectEvent> events = <ObjectEvent>[];
+    void listener(ObjectEvent event) {
+      if (event.object.runtimeType == FocusNode) {
+        events.add(event);
+      }
+    }
+    MemoryAllocations.instance.addListener(listener);
+
+    final FocusNode focusManager = FocusNode();
+
+    expect(events, hasLength(1));
+
+    focusManager.dispose();
+    MemoryAllocations.instance.removeListener(listener);
+  });
+
   testWidgets('FocusManager notifies listeners when a widget loses focus because it was removed.', (WidgetTester tester) async {
     final FocusNode nodeA = FocusNode(debugLabel: 'a');
     final FocusNode nodeB = FocusNode(debugLabel: 'b');

packages/flutter/test/widgets/memory_allocations_test.dart

@@ -6,20 +6,26 @@ import 'package:flutter/foundation.dart';
 import 'package:flutter/widgets.dart';
 import 'package:flutter_test/flutter_test.dart';
 
+    int _creations = 0;
+    int _disposals = 0;
+
 void main() {
   final MemoryAllocations ma = MemoryAllocations.instance;
 
-  setUp(() {
-    assert(!ma.hasListeners);
-  });
-
   test('Publishers dispatch events in debug mode', () async {
-    int eventCount = 0;
-    void listener(ObjectEvent event) => eventCount++;
+    void listener(ObjectEvent event) {
+      if (event is ObjectDisposed) {
+        _disposals++;
+      }
+      if (event is ObjectCreated) {
+        _creations++;
+      }
+    }
     ma.addListener(listener);
 
-    final int expectedEventCount = await _activateFlutterObjectsAndReturnCountOfEvents();
-    expect(eventCount, expectedEventCount);
+    final _EventStats actual = await _activateFlutterObjectsAndReturnCountOfEvents();
+    expect(actual.creations, _creations);
+    expect(actual.disposals, _disposals);
 
     ma.removeListener(listener);
     expect(ma.hasListeners, isFalse);
@@ -29,6 +35,8 @@ void main() {
     bool stateCreated = false;
     bool stateDisposed = false;
 
+    expect(ma.hasListeners, false);
+
     void listener(ObjectEvent event) {
       if (event is ObjectCreated && event.object is State) {
         stateCreated = true;
@@ -47,7 +55,7 @@ void main() {
     expect(stateCreated, isTrue);
     expect(stateDisposed, isTrue);
     ma.removeListener(listener);
-    expect(ma.hasListeners, isFalse);
+    expect(ma.hasListeners, false);
   });
 }
 
@@ -62,7 +70,8 @@ class _TestElement extends RenderObjectElement with RootElementMixin {
   _TestElement(): super(_TestLeafRenderObjectWidget());
 
   void makeInactive() {
-    assignOwner(BuildOwner(focusManager: FocusManager()));
+    final FocusManager newFocusManager = FocusManager();
+    assignOwner(BuildOwner(focusManager: newFocusManager));
     mount(null, null);
     deactivate();
   }
@@ -109,15 +118,22 @@ class _TestStatefulWidgetState extends State<_TestStatefulWidget> {
   }
 }
 
+
+class _EventStats {
+  int creations = 0;
+  int disposals = 0;
+}
+
 /// Create and dispose Flutter objects to fire memory allocation events.
-Future<int> _activateFlutterObjectsAndReturnCountOfEvents() async {
-  int count = 0;
+Future<_EventStats> _activateFlutterObjectsAndReturnCountOfEvents() async {
+  final _EventStats result = _EventStats();
 
-  final _TestElement element = _TestElement(); count++;
-  final RenderObject renderObject = _TestRenderObject(); count++;
+  final _TestElement element = _TestElement(); result.creations++;
+  final RenderObject renderObject = _TestRenderObject(); result.creations++;
 
-  element.makeInactive(); element.unmount(); count += 3;
-  renderObject.dispose(); count++;
+  element.makeInactive(); result.creations += 3; // 1 for the new BuildOwner, 1 for the new FocusManager, 1 for the new FocusScopeNode
+  element.unmount(); result.disposals += 2; // 1 for the old BuildOwner, 1 for the element
+  renderObject.dispose(); result.disposals += 1;
 
-  return count;
+  return result;
 }