81 lines
2.0 KiB
Dart
81 lines
2.0 KiB
Dart
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/**
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备忘录模式(Memento Pattern)
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意图:在不破坏封装性的前提下,捕获一个对象的内部状态,并在该对象之外保存这个状态。
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主要解决:所谓备忘录模式就是在不破坏封装的前提下,捕获一个对象的内部状态,并在该对象之外保存这个状态,这样可以在以后将对象恢复到原先保存的状态。
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何时使用:很多时候我们总是需要记录一个对象的内部状态,这样做的目的就是为了允许用户取消不确定或者错误的操作,能够恢复到他原先的状态,使得他有"后悔药"可吃。
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如何解决:通过一个备忘录类专门存储对象状态。
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*/
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main(List<String> args) {
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Originator originator = Originator();
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CareTaker careTaker = CareTaker();
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originator.setState("State #1");
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originator.setState("State #2");
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careTaker.add(originator.saveStateToMemento());
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originator.setState("State #3");
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careTaker.add(originator.saveStateToMemento());
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originator.setState("State #4");
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print("Current State: ${originator.getState()}");
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originator.getStateFromMemento(careTaker.get(0));
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print("First saved State: ${originator.getState()}");
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originator.getStateFromMemento(careTaker.get(1));
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print("Second saved State: ${originator.getState()}");
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}
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//////////////////////////////////////////////////////////////////
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///
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/// 创建 Memento 类
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///
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class Memento {
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String _state;
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Memento(this._state);
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String getState() {
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return _state;
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}
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}
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///
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/// 创建 Originator 类
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///
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class Originator {
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String _state;
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void setState(String state) {
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this._state = state;
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}
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String getState() {
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return _state;
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}
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Memento saveStateToMemento() {
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return Memento(_state);
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}
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void getStateFromMemento(Memento memento) {
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_state = memento.getState();
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}
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}
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///
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/// 创建 CareTaker 类
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///
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class CareTaker {
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List<Memento> _mementoList = List<Memento>();
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void add(Memento state) {
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_mementoList.add(state);
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}
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Memento get(int index) {
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return _mementoList[index];
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}
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}
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