Question

我想实现一个命令模式。我有以下内容：

public class State
{
    public int Number { get; set; }

    public void Execute(IAction action)
    {
        if (action.IsValid(this))
            action.Apply(this);
    }            
}

public interface IAction
{
    bool IsValid(State state);
    void Apply(State state);
}       

public class ActionSet5IfZero : IAction
{

    public bool IsValid(State state)
    {
        if (state.Number == 0)
            return true;
        else
            return false;
    }

    public void Apply(State state)
    {
        state.Number = 5;
    }
}

程序：

static void Main(string[] args)
{
    State s = new State();
    s.Execute(new ActionSet5IfZero());
}

按预期工作。我的问题开始了，当我想扩展State类时：

public class ExtendedState : State
{
    public int Number2 { get; set; }
}

现在，操作必须对ExtendedState应用更改。所以我想我会创建一个扩展动作，它有两个额外的函数，它们将ExtendedState作为参数：

public class ExtendedActionSet5IfZero : IAction
{

    public bool IsValid(State state)
    {
        throw new NotImplementedException();
    }

    public void Apply(State state)
    {
        throw new NotImplementedException();
    }

    public bool IsValid(ExtendedState state)
    {
        if (state.Number == 0 && state.Number2 == 0)
            return true;
        else
            return false;
    }

    public void Apply(ExtendedState state)
    {
        state.Number = 5;
        state.Number2 = 5;
    }
}

这是我不喜欢的，因为实现接口的功能变得多余。此外，我需要在我的Execute中创建一个新的ExtendedState函数，该函数使用新类型而不是IAction（否则将调用未实现的函数）。

我相信它可以以一种不错的OO方式完成。你能帮我吗？目的是创建一个可扩展的State类和IAction接口（甚至可能是通用的，我不知道），所以我可以扩展State但仍然是通用功能而无需额外的编码。

Answer 1

您可以向状态

添加虚拟SetNumber方法

public class State 
{ 
    public int Number { get; set; } 

    public virtual void SetNumber(int n)
    { 
        Number = n;
    }

    public void Execute(IAction action) 
    { 
        if (action.IsValid(this)) 
            action.Apply(this); 
    }             
}

在扩展状态下，你可以使用它

public class ExtendedState : State  {
    public int Number2 { get; set; }

    public orverride void SetNumber(int n)
    { 
        base.SetNumber(n);
        Number2 = n;
    }
}

然后将按照此

实施该操作

public void Apply(State state)        
{
    state.SetNumber(5);        
}

修改：

将Number声明为数组怎么样？

public class State { public int[] Numbers { get; private set; } public State() { Numbers = new int[1]; } ... }

然后该动作执行此操作

public void Apply(State state) { for (int i = 0; i < state.Numbers.Length; i++) { state.Numbers[i] = 5; } }

ExtendedState的构造函数会使用
初始化Numbers
Numbers = new int[2];

此外，您可以拥有单个数字的属性

public int Number { get { return Numbers[0]; } set { Numbers[0] = value; } }

和

public int Number2 { get { return Numbers[1]; } set { Numbers[1] = value; } }

Answer 2

您可以使用泛型：

interface IAction<TState> where TState: State
{
    bool IsValid(TState state);
    void Apply(TState state);
}

Answer 3

如何将StateContainer添加到State和Action：

public interface IStateContainer<TState, TAction> where TState : IState where TAction : IAction<TState> { 
    public TState State;
    public void Execute(TAction action);
}

public interface IState { }

public interface IAction<TState> where TState : IState {
    bool IsValid(TState state);
    void Apply(TState state);
}

然后您的原始课程可以替换为：

public class ValidatingStateContainer<TState, TAction> : IStateContainer<TState, TAction> {

    public ValidatingStateContainer(TState state) {
        State = state;
    }

    public TState State { get; private set; }

    public void Execute(TAction action)
    {
        if (action.IsValid(this))
            action.Apply(State);
    }
}

public class ActionSet5IfZero : IAction<NumberState>
{
    public boolean IsValid(NumberState state)
    {
        if (state.Number == 0)
            return true;
        else
            return false;
    }

    public void Apply(NumberState state)
    {
        state.Number = 5;
    }
}

public class ExtendedActionSet5IfZero : ActionSet5IfZero, IAction<TwoNumberState>
{   
    public boolean IsValid(TwoNumberState state)
    {
        if (base.IsValid(state) && state.Number2 == 0)
            return true;
        else
            return false;
    }

    public void Apply(TwoNumberState state)
    {
        base.Apply(state);
        state.Number2 = 5;
    }
}

public class NumberState : IState {
    public int Number { get; set; }
}

public class TwoNumberState : NumberState {
    public int Number2 { get; set; }
}

实现命令模式和多态

3 个答案: