packages/flutter/test/foundation/change_notifier_test.dart

 // Copyright 2016 The Chromium Authors. All rights reserved.
// Use of this source code is governed by a BSD-style license that can be
// found in the LICENSE file.

import 'package:flutter/foundation.dart';
import 'package:flutter_test/flutter_test.dart';

class TestNotifier extends ChangeNotifier {
  void notify() {
    notifyListeners();
  }
}

class HasListenersTester<T> extends ValueNotifier<T> {
  HasListenersTester(T value) : super(value);
  bool get testHasListeners => hasListeners;
}

class A {
  bool result = false;
  void test() { result = true; }
}

class B extends A with ChangeNotifier {
  @override
  void test() {
    notifyListeners();
    super.test();
  }
}

void main() {
  testWidgets('ChangeNotifier', (WidgetTester tester) async {
    final List<String> log = <String>[];
    final VoidCallback listener = () { log.add('listener'); };
    final VoidCallback listener1 = () { log.add('listener1'); };
    final VoidCallback listener2 = () { log.add('listener2'); };
    final VoidCallback badListener = () { log.add('badListener'); throw null; };

    final TestNotifier test = TestNotifier();

    test.addListener(listener);
    test.addListener(listener);
    test.notify();
    expect(log, <String>['listener', 'listener']);
    log.clear();

    test.removeListener(listener);
    test.notify();
    expect(log, <String>['listener']);
    log.clear();

    test.removeListener(listener);
    test.notify();
    expect(log, <String>[]);
    log.clear();

    test.removeListener(listener);
    test.notify();
    expect(log, <String>[]);
    log.clear();

    test.addListener(listener);
    test.notify();
    expect(log, <String>['listener']);
    log.clear();

    test.addListener(listener1);
    test.notify();
    expect(log, <String>['listener', 'listener1']);
    log.clear();

    test.addListener(listener2);
    test.notify();
    expect(log, <String>['listener', 'listener1', 'listener2']);
    log.clear();

    test.removeListener(listener1);
    test.notify();
    expect(log, <String>['listener', 'listener2']);
    log.clear();

    test.addListener(listener1);
    test.notify();
    expect(log, <String>['listener', 'listener2', 'listener1']);
    log.clear();

    test.addListener(badListener);
    test.notify();
    expect(log, <String>['listener', 'listener2', 'listener1', 'badListener']);
    expect(tester.takeException(), isNullThrownError);
    log.clear();

    test.addListener(listener1);
    test.removeListener(listener);
    test.removeListener(listener1);
    test.removeListener(listener2);
    test.addListener(listener2);
    test.notify();
    expect(log, <String>['badListener', 'listener1', 'listener2']);
    expect(tester.takeException(), isNullThrownError);
    log.clear();
  });

  test('ChangeNotifier with mutating listener', () {
    final TestNotifier test = TestNotifier();
    final List<String> log = <String>[];

    final VoidCallback listener1 = () { log.add('listener1'); };
    final VoidCallback listener3 = () { log.add('listener3'); };
    final VoidCallback listener4 = () { log.add('listener4'); };
    final VoidCallback listener2 = () {
      log.add('listener2');
      test.removeListener(listener1);
      test.removeListener(listener3);
      test.addListener(listener4);
    };

    test.addListener(listener1);
    test.addListener(listener2);
    test.addListener(listener3);
    test.notify();
    expect(log, <String>['listener1', 'listener2']);
    log.clear();

    test.notify();
    expect(log, <String>['listener2', 'listener4']);
    log.clear();

    test.notify();
    expect(log, <String>['listener2', 'listener4', 'listener4']);
    log.clear();
  });

  test('Merging change notifiers', () {
    final TestNotifier source1 = TestNotifier();
    final TestNotifier source2 = TestNotifier();
    final TestNotifier source3 = TestNotifier();
    final List<String> log = <String>[];

    final Listenable merged = Listenable.merge(<Listenable>[source1, source2]);
    final VoidCallback listener1 = () { log.add('listener1'); };
    final VoidCallback listener2 = () { log.add('listener2'); };

    merged.addListener(listener1);
    source1.notify();
    source2.notify();
    source3.notify();
    expect(log, <String>['listener1', 'listener1']);
    log.clear();

    merged.removeListener(listener1);
    source1.notify();
    source2.notify();
    source3.notify();
    expect(log, isEmpty);
    log.clear();

    merged.addListener(listener1);
    merged.addListener(listener2);
    source1.notify();
    source2.notify();
    source3.notify();
    expect(log, <String>['listener1', 'listener2', 'listener1', 'listener2']);
    log.clear();
  });

  test('Merging change notifiers ignores null', () {
    final TestNotifier source1 = TestNotifier();
    final TestNotifier source2 = TestNotifier();
    final List<String> log = <String>[];

    final Listenable merged = Listenable.merge(<Listenable>[null, source1, null, source2, null]);
    final VoidCallback listener = () { log.add('listener'); };

    merged.addListener(listener);
    source1.notify();
    source2.notify();
    expect(log, <String>['listener', 'listener']);
    log.clear();
  });

  test('Can dispose merged notifier', () {
    final TestNotifier source1 = TestNotifier();
    final TestNotifier source2 = TestNotifier();
    final List<String> log = <String>[];

    final ChangeNotifier merged = Listenable.merge(<Listenable>[source1, source2]);
    final VoidCallback listener = () { log.add('listener'); };

    merged.addListener(listener);
    source1.notify();
    source2.notify();
    expect(log, <String>['listener', 'listener']);
    log.clear();
    merged.dispose();

    source1.notify();
    source2.notify();
    expect(log, isEmpty);
  });

  test('Cannot use a disposed ChangeNotifier', () {
    final TestNotifier source = TestNotifier();
    source.dispose();
    expect(() { source.addListener(null); }, throwsFlutterError);
    expect(() { source.removeListener(null); }, throwsFlutterError);
    expect(() { source.dispose(); }, throwsFlutterError);
    expect(() { source.notify(); }, throwsFlutterError);
  });

  test('Value notifier', () {
    final ValueNotifier<double> notifier = ValueNotifier<double>(2.0);

    final List<double> log = <double>[];
    final VoidCallback listener = () { log.add(notifier.value); };

    notifier.addListener(listener);
    notifier.value = 3.0;

    expect(log, equals(<double>[ 3.0 ]));
    log.clear();

    notifier.value = 3.0;
    expect(log, isEmpty);
  });

  test('Listenable.merge toString', () {
    final TestNotifier source1 = TestNotifier();
    final TestNotifier source2 = TestNotifier();

    ChangeNotifier listenableUnderTest = Listenable.merge(<Listenable>[]);
    expect(listenableUnderTest.toString(), 'Listenable.merge([])');

    listenableUnderTest = Listenable.merge(<Listenable>[null]);
    expect(listenableUnderTest.toString(), 'Listenable.merge([null])');

    listenableUnderTest = Listenable.merge(<Listenable>[source1]);
    expect(
      listenableUnderTest.toString(),
      "Listenable.merge([Instance of 'TestNotifier'])",
    );

    listenableUnderTest = Listenable.merge(<Listenable>[source1, source2]);
    expect(
      listenableUnderTest.toString(),
      "Listenable.merge([Instance of 'TestNotifier', Instance of 'TestNotifier'])",
    );

    listenableUnderTest = Listenable.merge(<Listenable>[null, source2]);
    expect(
      listenableUnderTest.toString(),
      "Listenable.merge([null, Instance of 'TestNotifier'])",
    );
  });

  test('hasListeners', () {
    final HasListenersTester<bool> notifier = HasListenersTester<bool>(true);
    expect(notifier.testHasListeners, isFalse);
    void test1() { }
    void test2() { }
    notifier.addListener(test1);
    expect(notifier.testHasListeners, isTrue);
    notifier.addListener(test1);
    expect(notifier.testHasListeners, isTrue);
    notifier.removeListener(test1);
    expect(notifier.testHasListeners, isTrue);
    notifier.removeListener(test1);
    expect(notifier.testHasListeners, isFalse);
    notifier.addListener(test1);
    expect(notifier.testHasListeners, isTrue);
    notifier.addListener(test2);
    expect(notifier.testHasListeners, isTrue);
    notifier.removeListener(test1);
    expect(notifier.testHasListeners, isTrue);
    notifier.removeListener(test2);
    expect(notifier.testHasListeners, isFalse);
  });

  test('ChangeNotifier as a mixin', () {
    // We document that this is a valid way to use this class.
    final B b = B();
    int notifications = 0;
    b.addListener(() {
      notifications += 1;
    });
    expect(b.result, isFalse);
    expect(notifications, 0);
    b.test();
    expect(b.result, isTrue);
    expect(notifications, 1);
  });
}