没有事件发生

这是我的代码。我正在尝试使用箭头键移动球。 当我运行以上程序时，不显示球 （ 如果我将坐标更改为类似0,30球）， 并且事件未被触发，则球既不移动也不跳跃

What is the problem ？

 import java.awt.*; import java.awt.event.*; import javax.swing.*; class ControlledBall extends JPanel{ int diameter = 30; int height = 30; int x_Pos = 0; int y_Pos; ControlledBall() { JFrame fr = new JFrame("Controlled Ball"); this.setBackground(Color.black); fr.add(this); fr.setVisible(true); fr.setSize(600,400); y_Pos = this.getHeight() - diameter ; register(); repaint(); } public void register() { this.addKeyListener(new KeyAdapter() { public void keyPressed(KeyEvent ke) { if( ke.getKeyCode() == ke.VK_RIGHT ) { increment(); } else if( ke.getKeyCode() == ke.VK_LEFT ) { decrement(); } else if( ke.getKeyCode() == ke.VK_UP) { jump(); } } }); } public void paintComponent(Graphics g) { super.paintComponent(g); g.setColor( Color.blue ); g.fillOval( x_Pos , y_Pos , diameter , height ); System.out.println("testing..."); } public void increment() { x_Pos++; if( x_Pos > (this.getWidth() - diameter) ) { x_Pos = this.getWidth() - diameter; } repaint(); } public void decrement() { x_Pos--; if( x_Pos <= 0) { x_Pos = 0; } repaint(); } public void jump() { y_Pos++; if( y_Pos <=0 ) { y_Pos = 0; } repaint(); } public static void main( String args[] ) { new ControlledBall(); } } 

Answer 1

 import java.awt.*; import java.awt.event.*; import javax.swing.*; class ControlledBall extends JPanel{ int diameter = 30; int height = 30; int x_Pos = 0; int y_Pos; ControlledBall() { JFrame fr = new JFrame("Controlled Ball"); fr.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); this.setBackground(Color.red); setPreferredSize(new Dimension(400,300)); fr.add(this); fr.setVisible(true); // important! fr.pack(); //fr.setSize(600,400); y_Pos = this.getHeight()/2; register(); repaint(); } public void register() { // very important! setFocusable(true); this.addKeyListener(new KeyAdapter() { public void keyPressed(KeyEvent ke) { if( ke.getKeyCode() == ke.VK_RIGHT ) { increment(); } else if( ke.getKeyCode() == ke.VK_LEFT ) { decrement(); } else if( ke.getKeyCode() == ke.VK_UP) { jump(); } } }); } public void paintComponent(Graphics g) { super.paintComponent(g); g.setColor( Color.orange ); g.fillOval( x_Pos , y_Pos , diameter , height ); } public void increment() { x_Pos++; if( x_Pos > (this.getWidth() - diameter) ) { x_Pos = this.getWidth() - diameter; } repaint(); } public void decrement() { x_Pos--; if( x_Pos <= 0) { x_Pos = 0; } repaint(); } public void jump() { y_Pos++; if( y_Pos <=0 ) { y_Pos = 0; } repaint(); } public static void main( String args[] ) { new ControlledBall(); } } 

Answer 2

请使用以下代码替换代码，您将获得主JFrame已使用KeyEvent的真实情况。

为了确保获得所有这些事件，您不必在组件上注册，而是使用KeyboardFocusManager进行注册，它将接收发生的关键事件。

 ControlledBall() { JFrame fr = new JFrame("Controlled Ball"); this.setBackground(Color.black); this.setBorder( BorderFactory.createLineBorder( Color.white ) ); fr.add(this); fr.setSize(600,400); y_Pos = this.getHeight() - diameter ; register(); fr.setVisible(true); repaint(); fr.addKeyListener( new KeyAdapter() { public void keyPressed(KeyEvent e) { System.out.println("I am here....."); } }); } 

Answer 3

试试这个construtor并相应地修改你的jump, increment和decrement逻辑!!!! 您需要将侦听器添加到框架而不是面板。

int x_Pos = 30; int y_Pos = 15;

 ControlledBall() { JFrame fr = new JFrame("Controlled Ball"); this.setBackground(Color.black); fr.add(this); fr.setVisible(true); fr.setSize(600, 400); fr.addKeyListener(new KeyAdapter() { public void keyPressed(KeyEvent ke) { if (ke.getKeyCode() == ke.VK_RIGHT) { System.out.println("Right Key"); increment(); } else if (ke.getKeyCode() == ke.VK_LEFT) { System.out.println("Left Key"); decrement(); } else if (ke.getKeyCode() == ke.VK_UP) { System.out.println("Up Key"); jump(); } } }); y_Pos = this.getHeight() - diameter; //register(); repaint(); }