Can call ChangeNotifier.hasListeners after disposed (#108931)

Author: chunhtai

packages/flutter/lib/src/foundation/change_notifier.dart

@@ -170,11 +170,10 @@ class ChangeNotifier implements Listenable {
   /// [notifyListeners]; and similarly, by overriding [removeListener], checking
   /// if [hasListeners] is false after calling `super.removeListener()`, and if
   /// so, stopping that same work.
+  ///
+  /// This method returns false if [dispose] has been called.
   @protected
-  bool get hasListeners {
-    assert(ChangeNotifier.debugAssertNotDisposed(this));
-    return _count > 0;
-  }
+  bool get hasListeners => _count > 0;
 
   /// Register a closure to be called when the object changes.
   ///

packages/flutter/test/foundation/change_notifier_test.dart

@@ -349,6 +349,20 @@ void main() {
     expect(error, isNull);
   });
 
+  test('Can check hasListener on a disposed ChangeNotifier', () {
+    final HasListenersTester<int> source = HasListenersTester<int>(0);
+    source.addListener(() { });
+    expect(source.testHasListeners, isTrue);
+    FlutterError? error;
+    try {
+      source.dispose();
+      expect(source.testHasListeners, isFalse);
+    } on FlutterError catch (e) {
+      error = e;
+    }
+    expect(error, isNull);
+  });
+
   test('Value notifier', () {
     final ValueNotifier<double> notifier = ValueNotifier<double>(2.0);