C# 狀態模式和事件

Question

在 C# 中，事件只能由所屬類通過受保護的虛擬方法（如 OnClick、OnExit 等）觸發……我想做的是為我的一些復雜類實現 GOF 狀態模式。 到目前為止，一切都很好，只是我找不到從我的狀態類中觸發擁有類的事件的方法。

例如，我的按鈕有兩種狀態（向上和向下），DownState 類將檢查用戶輸入，並在必要時觸發按鈕的 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);
    }
}

我怎樣才能做到這一點？

Answer 1

在ButtonState類上設置事件或委托，以便您的按鈕可以調用。 將Button自動State屬性更改為一個后備存儲，該存儲在狀態更改時掛鈎和取消掛鈎此事件或委托。

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);
}

然后您可以在具體的 State 類中執行此操作

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);
    }
}