[英]Implementing command pattern and polymorphism
I want to implement a command pattern. 我想实现一个命令模式。 I have the following: 我有以下几点:
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;
}
}
And the program: 和程序:
static void Main(string[] args)
{
State s = new State();
s.Execute(new ActionSet5IfZero());
}
That works as expected. 如预期的那样。 My problem begins, when I would like to extend the State class: 当我想扩展State类时,我的问题开始了:
public class ExtendedState : State
{
public int Number2 { get; set; }
}
Now the action must apply changes on ExtendedState
. 现在,该操作必须在ExtendedState
上应用更改。 So I thought I would create extended action that has two additional functions that take ExtendedState
as a parameter: 所以我想我将创建具有两个附加函数的扩展操作,这些附加函数将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;
}
}
This is something I already do not like because the functions that implement the interface become redundant. 这是我不喜欢的,因为实现接口的功能变得多余。 Moreover I need to create a new Execute
function in my ExtendedState
that utilizes the new type and not IAction (otherwise not implemented functions get called). 此外,我需要在我的ExtendedState
中创建一个新的Execute
函数,该函数使用新类型而不使用IAction(否则将调用未实现的函数)。
I am sure it can be done in a nice OO way. 我相信可以通过一种很好的面向对象的方式来完成。 Can you help me out? 你能帮我吗? The aim is to create an extensible State class and IAction interface (maybe even generic, I do not know), so I can extend the State
but remain the generic functionality without additional coding. 目的是创建一个可扩展的State类和IAction接口(我不知道甚至可以是通用的),因此我可以扩展State
但保留通用的功能而无需额外的编码。
You could add a virtual SetNumber
method to state 您可以添加一个虚拟的SetNumber
方法来声明
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);
}
}
In the extended state you orverride it 在扩展状态下,您将其覆盖
public class ExtendedState : State {
public int Number2 { get; set; }
public orverride void SetNumber(int n)
{
base.SetNumber(n);
Number2 = n;
}
}
The action would then be implemented like this 然后将像这样执行该动作
public void Apply(State state)
{
state.SetNumber(5);
}
EDIT : 编辑 :
What about declaring Number as array? 将Number声明为数组呢?
public class State
{
public int[] Numbers { get; private set; }
public State()
{
Numbers = new int[1];
}
...
}
The action then does this 该动作然后执行此操作
public void Apply(State state)
{
for (int i = 0; i < state.Numbers.Length; i++) {
state.Numbers[i] = 5;
}
}
The constructor of ExtendedState
would initialize Numbers
with 的构造ExtendedState
将初始化Numbers
与
Numbers = new int[2];
In addition, you could have properties for the single numbers 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; }
}
and 和
public int Number2 {
get { return Numbers[1]; }
set { Numbers[1] = value; }
}
You could use generics: 您可以使用泛型:
interface IAction<TState> where TState: State
{
bool IsValid(TState state);
void Apply(TState state);
}
How about adding StateContainer to State and Action: 如何将StateContainer添加到State和Action中:
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);
}
Then your original classes can be replaced with: 然后,您的原始类可以替换为:
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; }
}
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