方法未系結到事件處理程式-有解無憂

我試圖在 winforms 中使用 MVC 模式，但是當我嘗試呼叫事件時它總是為空。我將 GameView 表單傳遞給 Game 類，我將 CityButtonPressed 方法系結到事件，但是當我運行它時，似乎沒有任何系結。

class Game
{
    private readonly IGameView _gameView;

    public Game(IGameView view)
    {
        _gameView = view;
        _gameView.CityButtonPressed  = CityButtonPressed;
    }

    public void CityButtonPressed(object sender,EventArgs e)
    {
          //do something
    }
}

public interface IGameView
{
   event EventHandler CityButtonPressed;
}

public partial class GameView : Form,IGameView
{
    public event EventHandler CityButtonPressed;

    public GameView()
    {
        InitializeComponent();
    }

    protected virtual void OnButtonPressed(EventArgs e)
    {
        CityButtonPressed?.Invoke(this, e);
    }

    private void button1_Click(object sender, EventArgs e)
    {
        OnButtonPressed(EventArgs.Empty);
    }
}

static class Program
{
    /// <summary>
    /// The main entry point for the application.
    /// </summary>
    [STAThread]
    static void Main()
    {
        Application.EnableVisualStyles();
        Application.SetCompatibleTextRenderingDefault(false);
        var gameView = new GameView();
        var game = new Game(gameView);
        Application.Run(new GameView());
    }
}

我究竟做錯了什么？

uj5u.com熱心網友回復：

這是您的代碼的精簡版本，表明它有效。

void Main()
{
    var view = new GameView();
    var game = new Game(view);
    view.OnButtonPressed();
}

public interface IGameView
{
    event EventHandler CityButtonPressed;
}

class Game
{
    private readonly IGameView _gameView;


    public Game(IGameView view)
    {
        _gameView = view;
        _gameView.CityButtonPressed  = CityButtonPressed;
    }

    public void CityButtonPressed(object sender, EventArgs e)
    {
        Console.WriteLine("Pressed");
    }
}

public partial class GameView : IGameView
{
    public event EventHandler CityButtonPressed;

    public void OnButtonPressed()
    {
        if (CityButtonPressed == null) 
            Console.WriteLine("null");
        CityButtonPressed?.Invoke(this, new EventArgs());
    }
}

當我運行它時，我會Pressed進入控制臺。我所做的只是重構您的代碼，使其降至運行所需的最小量。

看起來您沒有正確連接它，或者您沒有向我們展示所需的實際最少代碼量。

更新

您正在創建兩個GameView實體。有你的問題。

    var gameView = new GameView();
    var game = new Game(gameView);
    Application.Run(new GameView());

相反，試試這個：

    var gameView = new GameView();
    var game = new Game(gameView);
    Application.Run(gameView);

uj5u.com熱心網友回復：

確保在呼叫之前Game使用GameView實體實體化了類CityButtonPressed。例如：

private Game game;
    protected virtual void OnButtonPressed(EventArgs e)
    {
      game=  new Game(this);
        if (CityButtonPressed == null)   
            MessageBox.Show("null");  
        CityButtonPressed?.Invoke(this, e);
    }

這對您來說不是一個好的解決方案，因為您將在Game某處需要該實體，但CityButtonPressed不應再為空。

轉載請註明出處，本文鏈接：https://www.uj5u.com/qiye/407603.html

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