设计模式学习18 Memento

 应用场景:

在软件的构建过程中，某些对象的状态在转换的过程中，可能由于某种的需要，要求程序能够回溯到以前的状态。

Without violating encapsulation, capture and externalize an object's internal state so that the object can be restored to this state later. 仅仅是在外部新增加一个类，然后在这个类中保存类的状态信息。

实现代码：

// 只是封装状态，而不封装其他的方法。 class Rectangle : ICloneable { int x; int y; int weight; int height; public Rectangle(int x, int y, int weight, int height) { this.x = x; this.y = y; this.weight = weight; this.height = height; } public void MoveTo(int x, int y) { } public void ChangeWidth(int width) { this.weight = width; } public void ChangeHeight(int height) { this.height = height; } public void Draw() { } public object Clone() { return this.MemberwiseClone(); } public void SetValue(Rectangle r) { this.x = r.x; this.y = r.y; this.height = r.height; this.weight = r.weightl } public RectangleMemento CreateMemento() { RectangleMemento rm = new RectangleMemento(); rm.SetState(this.x, this.y, this.width, this.height); return rm; } public void SetMemento(RectangleMemento rm) { this.x = rm.x; this.y = rm.y; this.weight = rm.weight; this.height = rm.height; } } class RectangleMemento { internal int x; internal int y; int weight; int height; internal void SetState(int x, int y, int width, int height) { this.x = x; this.y = y; this.height = height; this.width = width; } } // GraphicsSystem处于另外的程序集 class GraphicsSystem { // 原发器对象 // 有必要对自身状态进行保存，然后在某个点出恢复对象 Rectangle r = new Rectangle(0, 0, 10, 10); // 备忘录对象 // 保存原发器对象 // Rectangle rSaved = new Rectangle(0, 0, 0, 0); RectangleMemento rSaved = new RectangleMemento(); public void Main() { Process(r); } public void Process(Rectangle rect) { // 在需要保存的地方来保存，然后在回复的 // 地方恢复 rSaved = r.CreateMemento(); // ... } public void SavedClick(object sender, EventArgs args) { } }