97 lines
2.1 KiB
Dart
97 lines
2.1 KiB
Dart
/**
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观察者模式(Observer Pattern)
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意图:定义对象间的一种一对多的依赖关系,当一个对象的状态发生改变时,所有依赖于它的对象都得到通知并被自动更新。
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主要解决:一个对象状态改变给其他对象通知的问题,而且要考虑到易用和低耦合,保证高度的协作。
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何时使用:一个对象(目标对象)的状态发生改变,所有的依赖对象(观察者对象)都将得到通知,进行广播通知。
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如何解决:使用面向对象技术,可以将这种依赖关系弱化。
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*/
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main(List<String> args) {
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Subject subject = Subject();
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HexaObserver(subject);
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OctalObserver(subject);
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BinaryObserver(subject);
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print("First state change: 15");
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subject.setState(15);
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print("\nSecond state change: 10");
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subject.setState(10);
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}
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//////////////////////////////////////////////////////////////////
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///
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/// 创建 Subject 类
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///
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class Subject {
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List<Observer> _observers = List<Observer>();
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int _state;
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int getState() {
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return _state;
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}
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void setState(int state) {
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this._state = state;
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notifyAllObservers();
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}
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void attach(Observer observer) {
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_observers.add(observer);
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}
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void notifyAllObservers() {
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for (Observer observer in _observers) {
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observer.update();
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}
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}
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}
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///
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/// 创建 Observer 类
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///
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abstract class Observer {
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Subject _subject;
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void update();
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}
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///
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/// 创建实体观察者类
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///
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class BinaryObserver extends Observer {
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BinaryObserver(Subject subject) {
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this._subject = subject;
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this._subject.attach(this);
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}
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@override
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void update() {
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print("Binary String: ${_subject.getState().toRadixString(2)}");
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}
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}
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class OctalObserver extends Observer {
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OctalObserver(Subject subject) {
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this._subject = subject;
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this._subject.attach(this);
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}
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@override
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void update() {
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print("Octal String: ${_subject.getState()}");
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}
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}
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class HexaObserver extends Observer {
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HexaObserver(Subject subject) {
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this._subject = subject;
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this._subject.attach(this);
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}
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@override
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void update() {
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print("Hex String: ${_subject.getState().toRadixString(16)}");
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}
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}
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