java - 在分层平面java中添加绘图

Question

我是Java Swing新手。我试图通过 layeredPane 在我的框架中添加由 paintComponent() 方法制作的绘图，但它没有显示在 JFrame

但是，如果我放置代码 frame.getContentPane().add(drawing) 并注释分层部分，则代码可以工作..

我做错了什么？

这是代码: 框架类

public class FrameTest extends JFrame  {

    static JFrame frame= new JFrame("Frame");


    public static void main(String[] args) {
        FrameTest test= new FrameTest ();   
    }

    public FrameTest (){
        this.openfrane();
        frame.setVisible(true);
        frame.setLocationRelativeTo(null);
    }

    public void openframe(){
        //window properties
        frame.setDefaultCloseOperation(EXIT_ON_CLOSE);
        frame.setSize(1000,600);
        frame.setResizable(false);

        //changing icon of window
        ImageIcon image = new ImageIcon("assets/icon.png");
        card.setIconImage(image.getImage());

        //label picture background
        JLabel background = new JLabel();
        ImageIcon back = new ImageIcon("assets/background.jpg");
        background.setIcon(back);
        background.setLocation(0,-125);
        background.setSize(1000,700);

        //label for first 
        JLabel first = new JLabel("Sample text");
        first.setForeground(Color.RED);
        first.setSize(500,200);
        first.setLocation(31, 150);

        Draw drawing = new Draw();

        JLayeredPane layers = new JLayeredPane();
        layers.add(drawing, new Integer(3));
        layers.add(first, new Integer(2));
        layers.add(background,new Integer(1));
        frame.setLayeredPane(layers);

    }
}

绘图类:

public class Draw extends JPanel {

    public void paintComponent(Graphics g) {
        Graphics2D g2 = (Graphics2D)g;

        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING,RenderingHints.VALUE_ANTIALIAS_ON);

        int startX = 00;
        int startY = 00;

        // First circle
        Ellipse2D circle1 = new Ellipse2D.Double(startX, startY, 30, 30);
        g2.setColor(Color.Black);
        g2.draw(circle1);
        g2.fill(circle1);

        // Second circle
        Ellipse2D circle2 = new Ellipse2D.Double(startX+20, startY, 30, 30);
        g2.setColor(Color.Black);
        g2.draw(circle2);
        g2.fill(circle2);
     }
}

Answer 1

i am trying to add the drawing made by the paintComponent() method in my a frame through layeredPane but it is not showing in the JFrame

您的 DrawPanel 没有尺寸，因此尺寸为 (0, 0) 并且没有任何可绘制的内容。

However if i place the code frame.getContentPane().add(drawing) and comment the Layered part the code works..

当您将 DrawPanel 直接添加到内容 Pane 时，面板将添加到“CENTER”，并且布局管理器会自动将面板大小设置为框架中的可用空间。