java - 按下某个键时重新绘制 JPanel。 ( java )

Question

我正在使用 Java 开发 Swing 应用程序，当按下某个键时我无法更新我的 JPanel...

这是 JFrame

import javax.swing.JFrame;
import javax.swing.SwingUtilities;

public class PixelDraw {

public static void main(String[] args) {
    SwingUtilities.invokeLater(new Runnable() {
        public void run() {
            createAndShowGUI(); 
        }
    });
}

private static void createAndShowGUI() {
    //System.out.println("Created GUI on EDT? "+
    //SwingUtilities.isEventDispatchThread());

    JFrame f = new JFrame("Swing Paint Demo");
    f.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    f.add(new DrawingPanel());
    f.pack();
    f.setLocationRelativeTo(null);
    f.setVisible(true);
}
}

这是我的面板:

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.event.KeyEvent;
import java.awt.event.KeyListener;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;

import javax.swing.BorderFactory;
import javax.swing.JPanel;


public class DrawingPanel extends JPanel implements KeyListener {

    private static final long serialVersionUID = 1L;

    private int scale = 5;
    private int bits = 8 * scale;
    private int cols = 32;

    //Selection rectangle:
    private int sX = 0;
    private int sY = 0;
    private int sWidth = 1;
    private int sHeight = 1;

    private Color BackFill = new Color(140, 140, 140);
    private Color BackBorder = new Color(70, 70, 70);

    public DrawingPanel() {
        //setBorder(BorderFactory.createLineBorder(Color.red));

        addKeyListener(this);

        addMouseListener(new MouseAdapter() {
            public void mousePressed(MouseEvent e) {
                //On Click:

            }
        });

        addMouseMotionListener(new MouseAdapter() {
            public void mouseDragged(MouseEvent e) {
                //On Dragg:
            }
        });

    }

    public void keyPressed(KeyEvent evt) {
        int keyCode = evt.getKeyCode();

        if (keyCode == KeyEvent.VK_LEFT) {
            sY = (sY == 0) ? sY :  sY-1;
            if (evt.isControlDown()) {
                sWidth = (sY == 0) ? sWidth : sWidth+1;
            }
        }

        else if (keyCode == KeyEvent.VK_RIGHT) {
            sY = (sY == cols) ? sY :  sY+1;
            if (evt.isControlDown()) {
                sWidth = (sY == cols) ? sWidth : sWidth+1;
            }
        }

        else if (keyCode == KeyEvent.VK_UP) {
            sX = (sX == 0) ? sX :  sX-1;
            if (evt.isControlDown()) {
                sWidth = (sY == 0) ? sWidth : sHeight+1;
            }
        }
        else if (keyCode == KeyEvent.VK_DOWN){
            sX = (sX == cols) ? sX :  sX+1;
            if (evt.isControlDown()) {
                sWidth = (sY == cols) ? sWidth : sHeight+1;
            }
        }

        this.repaint();
    }

    public void keyReleased(KeyEvent evt) {
    }

    public void keyTyped(KeyEvent evt) {
    }

    public Dimension getPreferredSize() {
        return new Dimension(800, 800);
    }

    protected void paintComponent(Graphics g) {
        super.paintComponent(g);       

        //paint Background
        for(int x = 0; x <= (cols-1) * bits; x += bits) {
            for(int y = 0; y <= (cols-1) * bits; y += bits){
                g.setColor(BackBorder);
                g.fillRect(x, y, bits, bits);
                g.setColor(BackFill);
                g.fillRect(x+(1*scale), y+(1*scale), bits-(1*scale), bits-(1*scale));
            }
        }

        //paint selection
        g.setColor(Color.red);
        g.drawRect(sX*bits, sY*bits, (sWidth*bits)+(scale-1), (sHeight*bits)+(scale-1));
    }  
}

因此，它应该做的是在按下箭头时移动红色矩形(如选区)...或者在按下 ctrl+箭头时扩大选区...

Answer 1

您遇到了 KeyListeners 的一个常见问题——缺少组件焦点。要使 KeyListener 起作用，被监听的组件必须既可聚焦又具有用户焦点，这两者对于您的应用程序都是不正确的。

一个快速解决方法是通过 setFocusable(true) 让您的 JPanel 可聚焦，然后通过 requestFocusInWindow() 获得焦点。

public DrawingPanel() {
  addKeyListener(this);
  setFocusable(true);
  requestFocusInWindow();
}

但是一旦将另一个组件(例如 JButton 或文本组件)添加到您的 GUI 并窃取了焦点，这就会失败。更好的长期解决方案是使用键绑定(bind)。

---

编辑

请查看the Key Bindings Tutorial .此外，如果您在该网站上搜索我的带有键绑定(bind)的帖子，您会看到一些不错的示例。 For example .