Undo/Redo实现

一 使用Command模式如下：

二使用Singleton的UndoManager如下：

三C#的类代码如下：

public interface ICommand
{
   void Execute();
   void Reverse();
}

public class ACommand : ICommand
{
   void Execute(){};
   void Reverse(){};
}

public class BCommand : ICommand
{
   void Execute(){};
   void Reverse(){};
}

public class CCommand : ICommand
{
   void Execute(){};
   void Reverse(){};
}

public class UndoManager 
{
    public UndoManager()
    {
      UndoStack = new Stack<ICommand>();
      RedoStack = new Stack<ICommand>();
    } 

    public Stack<ICommand> UndoStack { get; protected set; }
    public Stack<ICommand> RedoStack { get; protected set; }

    public bool CanUndo { get { return UndoCommands.Count > 0; } }
    public bool CanRedo { get { return RedoCommands.Count > 0; } }


    public void Execute(ICommand command)
    {
      if (command == null) return;
      // Execute command
      command.Execute();      
      UndoStack.Push(command);
      // Clear the redo history upon adding new undo entry. 
      // This is a typical logic for most applications
      RedoStack.Clear();
    }

    public void Undo()
    {
      if (CanUndo)
      {
        ICommand command = UndoStack.Pop();
        if(command != null)
        {
            command.Reverse();
            RedoStack.Push(command);
        }
      }
    }


    public void Redo()
    {
      if (CanRedo)
      {
        ICommand command = RedoStack.Pop();
        if (command != null)
        {
          command.Execute(); 
          UndoStack.Push(command);
        }        
      }
    }
}

完！