C＃状态模式和事件

Posted 2021-04-08

在C＃中，只有拥有类的事件才能通过受保护的虚拟方法（例如OnClick，OnExit等）触发事件。我想做的就是为某些复杂的类实现GOF状态模式。到目前为止，一切工作都很好，除了我找不到从状态类中触发拥有类事件的方法。

例如，我的按钮有两种状态（上和下），DownState类将检查用户输入，并在必要时触发按钮的Click事件。

public class Button
{
    public Button()
    {
        State = new ButtonStateNormal(this);
    }

    public event EventHandler<MouseEventArgs> Click;
    public ButtonState State { get; set; }

    protected virtual void OnClick(MouseEventArgs e)
    {
        if (Click != null)
            Click(this, e);
    }
}

public class ButtonStateNormal : ButtonState
{
    Button button;
    public ButtonStateNormal(Button button)
    {
        this.button = button;
    }

    public override void CheckForInput()
    {
        //...
        //Check for user input and change the state
        //...
        button.State = new ButtonStateDown(button);
    }
}

public class ButtonStateDown : ButtonState
{
    Button button;
    public ButtonStateDown(Button button)
    {
        this.button = button;
    }

    public override void CheckForInput()
    {
        //...
        //Check for user input, fire the event of the button and change the state
        //...
        button.OnClick(new MouseEventArgs(mouse.X, mouse.Y)); //I want to do this, obviously it won't work this way
        button.State = new ButtonStateNormal(button);
    }
}

我该怎么做？

答案

在ButtonState类上设置事件或委托，以便您的按钮可以调用。使用后备存储将您在State中的自动Button属性更改为一个属性，该属性可在状态改变时钩住和解钩此事件或委托。

public class Button
{
    public Button()
    {
        State = new ButtonStateNormal(this);
    }
    private ButtonState _state;
    public event EventHandler<MouseEventArgs> Click;
    public ButtonState State
    {
        protected get
        {
            return _state;
        }
        set
        {
            if (_state == value)
                return;
            if (_state != null)
                _state.Click -= OnClick;
            if (value != null)
                value.Click += OnClick;

            _state = value;

        }
    }

    protected virtual void OnClick(MouseEventArgs e)
    {
        if (Click != null)
            Click(this, e);
    }

    public void CheckForInput(){
        State.CheckForInput();
    }
}

public abstract class ButtonState
{
    public abstract void CheckForInput();
    public ClickDelegate Click;
    public delegate void ClickDelegate(MouseEventArgs a);
}

然后您可以在具体的State类中执行此操作

public class ButtonStateDown : ButtonState
{
    Button button;
    public ButtonStateDown(Button button)
    {
        this.button = button;
    }

    public void CheckForInput()
    {
        //...
        //Check for user input, fire the event of the button and change the state
        //...
        if(Click != null)
            Click(new MouseEventArgs(mouse.X, mouse.Y))
        button.State = new ButtonStateNormal(button);
    }
}