使用KeyListener与Java [英] Using KeyListener with Java
问题描述
对于作业作业，我需要创建一个基本上显示球的程序，用户应该可以使用左键和右键移动它。但是，程序没有响应键。我不知道错误在哪里，如果有人可以帮助我非常感激！这是代码：
public class GraphicsComponent extends JComponent
{
Ellipse2D.Double ball = new Ellipse2D （200，400，80，80）;
public void paintComponent（Graphics g）
{
Graphics2D g2 =（Graphics2D）g;
g2.setColor（Color.RED）;
g2.fill（ball）;
g2.draw（ball）;
}
}
public class BallViewer
{
public static void main（String [] args）
{
JFrame frame = new JFrame（）; //创建一个名为框架的新JFrame
frame.setSize（600,600）; //调用隐式参数框架
frame.setTitle（Move this Ball）的方法setSize; //设置框架的标题
frame.setDefaultCloseOperation（JFrame.EXIT_ON_CLOSE）;
final GraphicsComponent g = new GraphicsComponent（）; //创建一个名为g的GraphicsComponent，是最终的，以便内部类可以访问它
frame.add（g）; //将组件g添加到框架
frame.setVisible真正）; //设置框架的可见性
class PressListener实现KeyListener //创建一个实现MouseListener接口的内部类
{
public void keyPressed（KeyEvent e）
{
if（e.getKeyCode（）== KeyEvent.VK_LEFT）
{
System.out.println（Left key pressed）;
}
if（e.getKeyCode（）== KeyEvent.VK_RIGHT）
{
System.out.println（Right key pressed）;
}
}
public void keyReleased（KeyEvent e）
{
}
public void keyTyped（KeyEvent e）
{
}
}
PressListener listener = new PressListener（）;
g.addKeyListener（listener）;
}
}
code> KeyListener 只有当注册的组件可以对焦并且具有可调整性时才会响应， JComponent 在默认情况下不能对焦。 >
而是使用键绑定，他们为您节省了与 KeyListener相关的焦点问题的烦恼。$ / $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $同样会使 Ellipse2D 移动有问题，首先将其位置设置为 0x0 并翻译 Graphics 您要绘制球的位置的上下文
作为示例...
InputMap im = getInputMap（WHEN_IN_FOCUSED_WINDOW）;
ActionMap am = getActionMap（）;
im.put（KeyStroke.getKeyStroke（KeyEvent.VK_UP，0），up）;
im.put（KeyStroke.getKeyStroke（KeyEvent.VK_DOWN，0），down）;
im.put（KeyStroke.getKeyStroke（KeyEvent.VK_LEFT，0），left）;
im.put（KeyStroke.getKeyStroke（KeyEvent.VK_RIGHT，0），right）;
am.put（up，new DeltaAction（0，-10））;
am.put（down，new DeltaAction（0，10））;
am.put（left，new DeltaAction（-10，0））;
am.put（right，new DeltaAction（10，0））;
而$ code> DeltaAction ... point 是 Ellipse 被绘的位置。
public class DeltaAction extends AbstractAction {
private int deltaX;
private int deltaY;
public DeltaAction（int deltaX，int deltaY）{
this.deltaX = deltaX;
this.deltaY = deltaY;
}
@Override
public void actionPerformed（ActionEvent e）{
point.x + = deltaX;
point.y + = deltaY;
if（point.x< 0）{
point.x = 0;
} else if（point.x + DIAMETER> = getWidth（））{
point.x = getWidth（） - DIAMETER;
}
if（point.y< 0）{
point.y = 0;
} else if（point.y + DIAMETER> = getHeight（））{
point.y = getHeight（） - DIAMETER;
}
repaint（）;
}
}
For a homework assignment I need to create a program that essentially displays a ball and the user should be able to move it using the left and right keys. However, the program isn't responding to the keys. I don't know where the bug is, and I'd appreciate it very much if someone could help! This is the code:
public class GraphicsComponent extends JComponent
{
Ellipse2D.Double ball = new Ellipse2D.Double(200, 400, 80, 80);
public void paintComponent(Graphics g)
{
Graphics2D g2 = (Graphics2D) g;
g2.setColor(Color.RED);
g2.fill(ball);
g2.draw(ball);
}
}
public class BallViewer
{
public static void main(String[] args)
{
JFrame frame = new JFrame(); //creates a new JFrame called frame
frame.setSize(600,600); //invokes the method setSize on the implicit parameter frame
frame.setTitle("Move this Ball"); //sets the title of the fram
frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
final GraphicsComponent g = new GraphicsComponent(); //creates a new GraphicsComponent called g, is final so that the inner class can access it
frame.add(g);//adds component g to the frame
frame.setVisible(true); //sets the visibility of the frame
class PressListener implements KeyListener //creates an inner class that implements MouseListener interface
{
public void keyPressed(KeyEvent e)
{
if (e.getKeyCode() == KeyEvent.VK_LEFT)
{
System.out.println("Left key pressed");
}
if (e.getKeyCode() == KeyEvent.VK_RIGHT)
{
System.out.println("Right key pressed");
}
}
public void keyReleased(KeyEvent e)
{
}
public void keyTyped(KeyEvent e)
{
}
}
PressListener listener = new PressListener();
g.addKeyListener(listener);
}
}
KeyListener will only respond when the component it's registered is focusable AND has focusable, JComponent is not focusable by default.
Instead, use key bindings, they save you all the hassel of messing with focus issues related to KeyListener
You're also going to have problems with making the Ellipse2D move, start by setting it's position as 0x0 and translating the Graphics context to the position you want to paint the ball
As an example...
InputMap im = getInputMap(WHEN_IN_FOCUSED_WINDOW);
ActionMap am = getActionMap();
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_UP, 0), "up");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_DOWN, 0), "down");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_LEFT, 0), "left");
im.put(KeyStroke.getKeyStroke(KeyEvent.VK_RIGHT, 0), "right");
am.put("up", new DeltaAction(0, -10));
am.put("down", new DeltaAction(0, 10));
am.put("left", new DeltaAction(-10, 0));
am.put("right", new DeltaAction(10, 0));
And the DeltaAction...point is the location at which the Ellipse is painted...
public class DeltaAction extends AbstractAction {
private int deltaX;
private int deltaY;
public DeltaAction(int deltaX, int deltaY) {
this.deltaX = deltaX;
this.deltaY = deltaY;
}
@Override
public void actionPerformed(ActionEvent e) {
point.x += deltaX;
point.y += deltaY;
if (point.x < 0) {
point.x = 0;
} else if (point.x + DIAMETER >= getWidth()) {
point.x = getWidth() - DIAMETER;
}
if (point.y < 0) {
point.y = 0;
} else if (point.y + DIAMETER >= getHeight()) {
point.y = getHeight() - DIAMETER;
}
repaint();
}
}
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