java - 尝试从 JComponent 调用函数时传递按钮时出现 MVC 函数错误

Question

我不确定我是否在做一个正确的 MVC，但我无法从我的 View 中执行 Clear()。

主要

public class Main{
    public static void main(String[] args) {
        Model model = new Model();
        final View view = new View();
        Controller controller = new Controller(view, model);

        javax.swing.SwingUtilities.invokeLater(new Runnable() {
            @Override
            public void run() {
                view.showView();
            }
        });
    }
}

模型

public class Model {
    DrawPad drawPad = new DrawPad();
        Model() {
    }
    public void Clear() {
        drawPad.clear();
        System.out.print("HELP");
    }
}

查看

public class View extends JFrame {
    JButton clearButton = new JButton("Clear");
    DrawPad drawPad = new DrawPad();
    Model model;

    public void showView() {
        JFrame frame = new JFrame();
        drawPad.DrawPad();
        frame.add(drawPad, BorderLayout.CENTER);
        frame.add(clearButton, BorderLayout.SOUTH);
        frame.setSize(280, 300);
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
    }

    public void addButtonActionListener(ActionListener clr) {
        clearButton.addActionListener(clr);
    }
}

Controller

public class Controller implements ActionListener {
    View view;
    Model model;

    Controller(View v, Model m) {
        this.view = v;
        this.model = m;
        view.addButtonActionListener(this);
    }

    public void actionPerformed(ActionEvent e) {
        model.Clear();
        System.out.print("H");
    }
}

J组件

class DrawPad extends JComponent {
    Image image;
    public Graphics2D graphics2D;
    int currentX, currentY, oldX, oldY;

    public void DrawPad() {
        setDoubleBuffered(false);
        addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                oldX = e.getX();
                oldY = e.getY();
            }
        });

        addMouseMotionListener(new MouseMotionAdapter() {
            public void mouseDragged(MouseEvent e) {

                currentX = e.getX();
                currentY = e.getY();
                if (graphics2D != null)
                    graphics2D.drawLine(oldX, oldY, currentX, currentY);
                repaint();
                oldX = currentX;
                oldY = currentY;
            }
        });
    }

    public void paintComponent(Graphics g) {
        if (image == null) {
            image = createImage(getSize().width, getSize().height);
            graphics2D = (Graphics2D) image.getGraphics();
            graphics2D.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
            clear();
        }
        g.drawImage(image, 0, 0, null);
    }

    public void clear() {
        System.out.println("Test");
        graphics2D.setPaint(Color.white);
        graphics2D.fillRect(0, 0, getSize().width, getSize().height);
        graphics2D.setPaint(Color.black);
        repaint();
    }
}

如果我从我的 View 中使用事件监听器并创建一个 drawPad 并直接调用 clear()，我就能够执行。但是，当我调用 clear form 模型和 Controller 时，它会抛出错误。

如果我做错了什么，有什么想法吗？也许我遗漏了什么？

Answer 1

绕过尝试将纯 MVC 范例包装在非纯 MVC 范例之上的问题以及您的 DrawPad 实际上应该有自己的 MVC 包装的问题，您需要提供一个Observer Pattern这允许 Controller 监视 Model 中可能发生的更改。

例如……

public interface ModelListener {
    public void modelCleared(Model model);
}

public class Model {

    private List<ModelListener> listeners;

    Model() {
        listeners = new ArrayList<>(25);
    }

    public void addModelListener(ModelListener listener) {
        listeners.add(listener);
    }

    public void Clear() {
        System.out.print("HELP");
        for (ModelListener listener : listeners) {
            listener.modelCleared(this);
        }
    }
}

然后，当您创建Controller 时，您将向模型注册一个ModelListener...

public class Controller implements ActionListener {

    View view;
    Model model;

    Controller(View v, Model m) {
        this.view = v;
        this.model = m;
        model.addModelListener(new ModelListener() {
            @Override
            public void modelCleared(Model model) {
                view.clear();
            }
        });
        view.addButtonActionListener(this);
    }

    public void actionPerformed(ActionEvent e) {
        model.Clear();
        System.out.print("H");
    }
}