在运行时从另一个类中绘制 JPanel

Question

我有一个类 Roundabout(JFrame)、Surface(JPanel) 和 Spawn。在 Surface paintComponent 我已经画了一些红绿灯，因为它们总是在环形交叉路口。但我也想在运行时绘制组件。所以我在 JFrame 中添加了一个 mousePressed 事件，我在这里调用的方法最终从 Spawn.java 调用了spawnPedestrian，因为println，我可以看到这一点。但是当spawnPedestrian 被调用时，什么都没有画！如果我在 Surface 类中创建一个行人并绘制它，它就可以工作。我怎样才能使spawnPedestrian 工作？我尝试包含最小代码 sn-p（见下文）。

human.png

roundabout.png

public class Spawn {

public void spawnPedestrian(){
    //Create a new pedestrian.

    Pedestrian p = new Pedestrian(100,100);

    Roundabout.getSurface().add(p);
    Roundabout.getSurface().revalidate();
    Roundabout.getSurface().repaint();

   }
 }

public class Roundabout extends JFrame{

static Surface surface=new Surface(); 

public Roundabout(){
    initUI();
}

private void initUI() {

    setTitle("Roundabout");
    setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);

    add(surface); 

    this.addMouseListener(new MouseAdapter() {// empty implementation of all
        // MouseListener`s methods
        @Override
        public void mousePressed(MouseEvent e) {
            System.out.println(e.getX() + "," + e.getY());
            Spawn spawn=new Spawn();
            spawn.spawnPedestrian();

        }
    });

    setSize(1618,850);
    setLocationRelativeTo(null);

}

public static JPanel getSurface() {  
    return surface;
}

public static void main(String[] args) {

    //Swing thread
    SwingUtilities.invokeLater(new Runnable() {
        @Override
        public void run() {
            Roundabout roundabout=new Roundabout(); 
            roundabout.setVisible(true);        
        }
    });                    
}

class Surface extends JPanel {

Track track=new Track();  

@Override
public void paintComponent(Graphics g) {

    super.paintComponent(g);    

    //Make sure the track is painted first
    track.paint(g);

    }

}

public class Track{

BufferedImage track;
Point trackPosition;
static final Point TRACK_POS = new Point(0, 0);
static final Point SENSOR_POS = new Point(250, 70);

public Track(){
    try {
        track = ImageIO.read(Roundabout.class.getResource("images/roundabout.png"));
    } catch (Exception ex) {
        System.out.println("Problem loading track image: " + ex);
    }
    trackPosition=new Point(TRACK_POS.x,TRACK_POS.y);
}

public void paint(Graphics g)
 {
    g.drawImage(track,TRACK_POS.x, TRACK_POS.y, null);
 }
}


public class Spawn {


//Needs x/y pos
public void spawnPedestrian(){
    Pedestrian p = new Pedestrian(30,50);

    System.out.println("Spawn me ");

    Roundabout.getSurface().add(p);
    Roundabout.getSurface().revalidate();
    Roundabout.getSurface().repaint();


    }
  }
}

public class Pedestrian extends JComponent {

BufferedImage pedestrian;
Point pedestrianPosition;
double pedestrianRotation = 0;
int pedestrianW, pedestrianH;

public Pedestrian(int x, int y){
    try {
        pedestrian = ImageIO.read(Car.class.getResource("images/human.png"));
    } catch (IOException e) {
        System.out.println("Problem loading pedestrian images: " + e);
    }

    pedestrianPosition = new Point(x,y);
    pedestrianW = pedestrian.getWidth();
    pedestrianH = pedestrian.getHeight();

}

public void paint(Graphics g) {
    Graphics2D g2d = (Graphics2D) g.create();
    g2d.rotate(Math.toRadians(pedestrianRotation), pedestrianPosition.x, pedestrianPosition.y);
    g2d.drawImage(pedestrian, pedestrianPosition.x, pedestrianPosition.y, null);
}

编辑：以为我通过将Surface 布局设置为null 并使用setBounds 为Pedestrian 解决了这个问题。但是我将图像向右移动得越多，我必须在setBounds()中设置height和width就越高。谁能帮忙？

编辑：修改了我的帖子，现在它是一个可运行的示例，您只需为Track 和Pedestrian 选择自己的图像。

编辑：一个复制粘贴操作来添加代码和图像。

Answer 1

当您编写Roundabout.getSurface().add(p); 时，您正在向JPanel 对象添加一个JComponent。 JPanel 必须有一个布局来显示子组件。默认情况下，这是FlowLayout（请参阅doc）。 FlowLayout 旨在连续显示组件旁边的其他组件。它不支持在任意坐标显示组件。

我不确定为什么不显示行人，但原因可能是它们的维度为 0x0。您可以使用以下方法轻松检查：

p.setPreferredSize(new Dimension(50,50));

根据您的需要，您可以采用不同的方法：Surface 可以是一个简单的 Canvas，而不是扩展 JPanel，它包含一个“Paintables”列表，例如行人。在Surface.paintComponent() 中，您可以调用每个Paintable.paint()，为它们提供Graphics 对象：

interface Paintable {
   public void paint(Graphics2D g);
}

class Pedestrian implements Paintable {
   public double x, y;
   public void paint(Graphics2D g){
      Shape circle = new Ellipse2D.Double(x - 5, y - 5, 10, 10);
      g2d.draw(circle);
   }
}

class Surface extends Canvas {

   public List<Paintable> components = new ArrayList<Paintable>();

   @Override
   public void paintComponent(Graphics g) {

      super.paintComponent(g);    

      for(Paintable p : components)
         p.paint((Graphics2D) g);

   }

}

编辑：我发现您的代码存在一些其他问题：

• Surface.java：请注意，您使用默认的FlowLayout（因此它不会管理在给定坐标处显示组件）。
• Pedestrian.java：在构造函数末尾添加setPreferredSize(Roundabout.getSurface().getSize());。将您的 paint() 方法替换为：

.

public void paintComponent(Graphics g) {
    super.paintComponent(g);
    Graphics2D g2d = (Graphics2D) g;
    g2d.rotate(Math.toRadians(pedestrianRotation), 
        pedestrianPosition.x, pedestrianPosition.y);
    g2d.drawImage(pedestrian, pedestrianPosition.x,
        pedestrianPosition.y, null);
}

• RoundAbout.java：surface =new Surface(); 应在 initUI() 内部调用，以便在事件线程上实例化。