C# 备忘录模式讲解和代码示例

using System; using System.Collections.Generic; using System.Linq; using System.Threading; namespace RefactoringGuru.DesignPatterns.Memento.Conceptual { // The Originator holds some important state that may change over time. It // also defines a method for saving the state inside a memento and another // method for restoring the state from it. class Originator { // For the sake of simplicity, the originator's state is stored inside a // single variable. private string _state; public Originator(string state) { this._state = state; Console.WriteLine("Originator: My initial state is: " + state); } // The Originator's business logic may affect its internal state. // Therefore, the client should backup the state before launching // methods of the business logic via the save() method. public void DoSomething() { Console.WriteLine("Originator: I'm doing something important."); this._state = this.GenerateRandomString(30); Console.WriteLine($"Originator: and my state has changed to: {_state}"); } private string GenerateRandomString(int length = 10) { string allowedSymbols = "abcdefghijklmnopqrstuvwxyzABCDEFGHIJKLMNOPQRSTUVWXYZ"; string result = string.Empty; while (length > 0) { result += allowedSymbols[new Random().Next(0, allowedSymbols.Length)]; Thread.Sleep(12); length--; } return result; } // Saves the current state inside a memento. public IMemento Save() { return new ConcreteMemento(this._state); } // Restores the Originator's state from a memento object. public void Restore(IMemento memento) { if (!(memento is ConcreteMemento)) { throw new Exception("Unknown memento class " + memento.ToString()); } this._state = memento.GetState(); Console.Write($"Originator: My state has changed to: {_state}"); } } // The Memento interface provides a way to retrieve the memento's metadata, // such as creation date or name. However, it doesn't expose the // Originator's state. public interface IMemento { string GetName(); string GetState(); DateTime GetDate(); } // The Concrete Memento contains the infrastructure for storing the // Originator's state. class ConcreteMemento : IMemento { private string _state; private DateTime _date; public ConcreteMemento(string state) { this._state = state; this._date = DateTime.Now; } // The Originator uses this method when restoring its state. public string GetState() { return this._state; } // The rest of the methods are used by the Caretaker to display // metadata. public string GetName() { return $"{this._date} / ({this._state.Substring(0, 9)})..."; } public DateTime GetDate() { return this._date; } } // The Caretaker doesn't depend on the Concrete Memento class. Therefore, it // doesn't have access to the originator's state, stored inside the memento. // It works with all mementos via the base Memento interface. class Caretaker { private List<IMemento> _mementos = new List<IMemento>(); private Originator _originator = null; public Caretaker(Originator originator) { this._originator = originator; } public void Backup() { Console.WriteLine("\nCaretaker: Saving Originator's state..."); this._mementos.Add(this._originator.Save()); } public void Undo() { if (this._mementos.Count == 0) { return; } var memento = this._mementos.Last(); this._mementos.Remove(memento); Console.WriteLine("Caretaker: Restoring state to: " + memento.GetName()); try { this._originator.Restore(memento); } catch (Exception) { this.Undo(); } } public void ShowHistory() { Console.WriteLine("Caretaker: Here's the list of mementos:"); foreach (var memento in this._mementos) { Console.WriteLine(memento.GetName()); } } } class Program { static void Main(string[] args) { // Client code. Originator originator = new Originator("Super-duper-super-puper-super."); Caretaker caretaker = new Caretaker(originator); caretaker.Backup(); originator.DoSomething(); caretaker.Backup(); originator.DoSomething(); caretaker.Backup(); originator.DoSomething(); Console.WriteLine(); caretaker.ShowHistory(); Console.WriteLine("\nClient: Now, let's rollback!\n"); caretaker.Undo(); Console.WriteLine("\n\nClient: Once more!\n"); caretaker.Undo(); Console.WriteLine(); } } } 

Originator: My initial state is: Super-duper-super-puper-super. Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: oGyQIIatlDDWNgYYqJATTmdwnnGZQj Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: jBtMDDWogzzRJbTTmEwOOhZrjjBULe Caretaker: Saving Originator's state... Originator: I'm doing something important. Originator: and my state has changed to: exoHyyRkbuuNEXOhhArKccUmexPPHZ Caretaker: Here's the list of mementos: 12.06.2018 15:52:45 / (Super-dup...) 12.06.2018 15:52:46 / (oGyQIIatl...) 12.06.2018 15:52:46 / (jBtMDDWog...) Client: Now, let's rollback! Caretaker: Restoring state to: 12.06.2018 15:52:46 / (jBtMDDWog...) Originator: My state has changed to: jBtMDDWogzzRJbTTmEwOOhZrjjBULe Client: Once more! Caretaker: Restoring state to: 12.06.2018 15:52:46 / (oGyQIIatl...) Originator: My state has changed to: oGyQIIatlDDWNgYYqJATTmdwnnGZQj