Java用箭头键在gui中移动一个圆圈

Question

我正在尝试使用 keyEvent 向左移动一个圆圈。到目前为止，圆圈已在窗口上绘制，但并没有向左移动！我觉得问题在于我将 Window() 构造函数添加到容器的位置。控制台上没有输出告诉我它正在工作。所以我认为它甚至没有达到 KeyEvent 类。这是我的代码：

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Ellipse2D;
import javax.swing.*;


public class Window extends JPanel {

    private static Ellipse2D.Double circle;

    public Window() {
        super();
        int width = 400;
        int height = 400;
        circle = new Ellipse2D.Double(0.5 * width, 0.9 * height,
                0.1 * width, 0.05 * height);
        addKeyListener(new MoveCircle());
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponents(g);
        Graphics2D brush = (Graphics2D) g;
        int width = getWidth();
        int height = getHeight();
        g.clearRect(0, 0, width, height);
        brush.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
        brush.draw(circle);
    }

    public class MoveCircle implements KeyListener {

        @Override
        public void keyPressed(KeyEvent e) {
            System.out.println("Working on top!");
            if (e.getKeyCode() == KeyEvent.VK_LEFT) {
                System.out.println("Working on bottom!");
                circle.x++;
                repaint();
            }
        }

        @Override
        public void keyReleased(KeyEvent e) {
            // TODO Auto-generated method stub
        }

        @Override
        public void keyTyped(KeyEvent e) {
            // TODO Auto-generated method stub
        }
    }

    public static void main(String[] args) {
        Window window = new Window();
        JFrame frame = new JFrame();
        Container container = frame.getContentPane();
        container.add(new Window());
        frame.addKeyEvent(window.new MoveCircle());
        frame.setSize(800, 700);
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setVisible(true);
    }
}

Answer 1

实际上发生的事情是这样的，您将Window 添加到JFrame，但重点在于JFrame，所以当您在Keyboard 上键入时，这件事会转到JFrame 而不是KeyListener 附加到 Window 类。因此，为了克服它，您只需在Window 类的对象上调用requestFocusInWindow()。试试这段代码，我对 EDT 和其他东西做了一些修改。

import java.awt.*;
import java.awt.event.*;
import java.awt.geom.Ellipse2D;
import javax.swing.*;


public class Window extends JPanel {

    private static Ellipse2D.Double circle;
    private JFrame frame;

    public Window() {
        super();
        int width = 400;
        int height = 400;
        circle = new Ellipse2D.Double(0.5 * width, 0.9 * height,
                0.1 * width, 0.05 * height);        
    }

    public Dimension getPreferredSize()
    {
        return (new Dimension(frame.getWidth(), frame.getHeight()));
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponents(g);
        Graphics2D brush = (Graphics2D) g;
        int width = getWidth();
        int height = getHeight();
        g.clearRect(0, 0, width, height);
        brush.setRenderingHint(RenderingHints.KEY_ANTIALIASING,
                RenderingHints.VALUE_ANTIALIAS_ON);
        brush.draw(circle);
    }

    public class MoveCircle implements KeyListener {

        @Override
        public void keyPressed(KeyEvent e) {
            System.out.println("Working on top!");
            if (e.getKeyCode() == Event.ENTER) {
                System.out.println("Working on bottom!");
                double newX = circle.x - 1;
                circle.x = newX;
                repaint();
            }
        }

        @Override
        public void keyReleased(KeyEvent e) {
            // TODO Auto-generated method stub
        }

        @Override
        public void keyTyped(KeyEvent e) {
            // TODO Auto-generated method stub
        }
    }

    private void createAndDisplayGUI(Window window)
    {
        frame = new JFrame();
        Container container = frame.getContentPane();       
        container.add(window);
        window.addKeyListener(new MoveCircle());        
        frame.setSize(800, 700);
        frame.setDefaultCloseOperation(JFrame.DISPOSE_ON_CLOSE);
        frame.setVisible(true);
        window.requestFocusInWindow();
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable()
        {
            public void run()
            {
                Window window = new Window();
                window.createAndDisplayGUI(window);
            }
        });
    }
}

Answer 2

只有获得焦点的组件才会获得关键事件。您需要在某个时候调用 requestFocus()。

Answer 3

解决方案是将 KeyListener 添加到 JFrame。这样，当 JFrame 获得焦点时，所有的击键都会引发一个事件。