Make custom element dimensions provider broadcast null events, similar to the full screen one.

Author: ditman

lib/web_ui/lib/src/engine/view_embedder/dimensions_provider/custom_element_dimensions_provider.dart

@@ -17,23 +17,27 @@ import 'dimensions_provider.dart';
 /// All the measurements returned from this class are potentially *expensive*,
 /// and should be cached as needed. Every call to every method on this class
 /// WILL perform actual DOM measurements.
+///
+/// This broadcasts `null` size events, to match the implementation of the
+/// FullPageDimensionsProvider, but it could broadcast the size coming from the
+/// DomResizeObserverEntry. Further changes in the engine are required for this
+/// to be effective.
 class CustomElementDimensionsProvider extends DimensionsProvider {
   /// Creates a [CustomElementDimensionsProvider] from a [_hostElement].
   CustomElementDimensionsProvider(this._hostElement) {
     // Send a resize event when the page DPR changes.
     _dprChangeStreamSubscription = DisplayDprStream.instance.dprChanged.listen((_) {
-      _broadcastSize(computePhysicalSize());
+      _broadcastSize(null);
     });
 
     // Hook up a resize observer on the hostElement (if supported!).
     _hostElementResizeObserver = createDomResizeObserver((
       List<DomResizeObserverEntry> entries,
       DomResizeObserver _,
     ) {
-      entries
-          .map((DomResizeObserverEntry entry) =>
-              ui.Size(entry.contentRect.width, entry.contentRect.height))
-          .forEach(_broadcastSize);
+      for (final DomResizeObserverEntry _ in entries) {
+        _broadcastSize(null);
+      }
     });
 
     assert(() {
@@ -53,11 +57,11 @@ class CustomElementDimensionsProvider extends DimensionsProvider {
   // Handle resize events
   late DomResizeObserver? _hostElementResizeObserver;
   late StreamSubscription<double>? _dprChangeStreamSubscription;
-  final StreamController<ui.Size> _onResizeStreamController =
-      StreamController<ui.Size>.broadcast();
+  final StreamController<ui.Size?> _onResizeStreamController =
+      StreamController<ui.Size?>.broadcast();
 
   // Broadcasts the last seen `Size`.
-  void _broadcastSize(ui.Size size) {
+  void _broadcastSize(ui.Size? size) {
     _onResizeStreamController.add(size);
   }
 
@@ -72,7 +76,7 @@ class CustomElementDimensionsProvider extends DimensionsProvider {
   }
 
   @override
-  Stream<ui.Size> get onResize => _onResizeStreamController.stream;
+  Stream<ui.Size?> get onResize => _onResizeStreamController.stream;
 
   @override
   ui.Size computePhysicalSize() {

lib/web_ui/test/engine/view_embedder/dimensions_provider/custom_element_dimensions_provider_test.dart

@@ -109,23 +109,28 @@ void doTests() {
     });
 
     test('funnels resize events on sizeSource', () async {
+      EngineFlutterDisplay.instance.debugOverrideDevicePixelRatio(2.7);
+
       sizeSource
         ..style.width = '100px'
         ..style.height = '100px';
 
-      expect(await provider.onResize.first, const ui.Size(100, 100));
+      expect(provider.onResize.first, completes);
+      expect(provider.computePhysicalSize(), const ui.Size(270, 270));
 
       sizeSource
         ..style.width = '200px'
         ..style.height = '200px';
 
-      expect(await provider.onResize.first, const ui.Size(200, 200));
+      expect(provider.onResize.first, completes);
+      expect(provider.computePhysicalSize(), const ui.Size(540, 540));
 
       sizeSource
         ..style.width = '300px'
         ..style.height = '300px';
 
-      expect(await provider.onResize.first, const ui.Size(300, 300));
+      expect(provider.onResize.first, completes);
+      expect(provider.computePhysicalSize(), const ui.Size(810, 810));
     });
 
     test('funnels DPR change events too', () async {
@@ -140,14 +145,15 @@ void doTests() {
       final CustomElementDimensionsProvider provider = CustomElementDimensionsProvider(sizeSource);
 
       // The size that will be emitted by the provider eventually
-      final Future<ui.Size> newSize = provider.onResize.first;
+      final Future<ui.Size?> newSize = provider.onResize.first;
 
       // Set the mock DPR value
       EngineFlutterDisplay.instance.debugOverrideDevicePixelRatio(3.2);
       // Simulate the mediaQuery change event from the browser
       eventTarget.dispatchEvent(createDomEvent('Event', 'change'));
 
-      expect(await newSize, const ui.Size(10, 10) * 3.2);
+      expect(newSize, completes);
+      expect(provider.computePhysicalSize(), const ui.Size(32, 32));
     });
 
     test('closed by onHotRestart', () async {