顶部没有绘制矩形

Question

我有一个扩展JPanel的类"Map".我将它添加到扩展JFrame的类中.

public void paintComponent(Graphics g) {
        super.paintComponent(g);
        int width = Math.abs(startX - endX);
        int height= Math.abs(startY - endY);
        g.setColor(Color.RED);
        g.fillRect(startX, startY, width, height);
    }

我的"Map"类还包含一个带有图像的标签.如果图像小于窗口,当我绘制一个矩形时,可以看到它.简而言之,它属于标签.

Answer 1

paintComponent 是油漆链的"底部",因此这里绘制的任何东西都会出现在其他所有东西之下.

更好的解决方案可能是将Map面板添加到标签(JLabel适当地设置's布局管理器).

或者,创建一个"基地"面板上,设置它的布局管理器使用来OverlayLayout管理,并添加JLabel和Map面板给它.

当然,这将取决于你想要实现的目标......

更新了"标签上的面板"示例

基本上,这需要a JLabel,设置一个图标(作为背景图像),设置它的布局BorderLayout,然后添加一个JPanel.

请记住,JPanel默认情况下是不透明的,因此您需要使其透明;)

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class OverlayLabel {

    public static void main(String[] args) {
        new OverlayLabel();
    }

    public OverlayLabel() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    try {
                        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                    } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                        ex.printStackTrace();
                    }

                    JLabel background = new JLabel(new ImageIcon(ImageIO.read(new File("/path/to/image"))));
                    background.setLayout(new BorderLayout());
                    background.add(new TestPane());

                    JFrame frame = new JFrame("Testing");
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.add(background);
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setOpaque(false);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics g2d = (Graphics2D) g.create();
            int x = (getWidth() - 20) / 2;
            int y = (getHeight() - 20) / 2;
            g2d.setColor(Color.RED);
            g2d.fillRect(x, y, 20, 20);
            g2d.dispose();
        }

    }

}

更新了示例 OverlayLayout

OverlayLayout 基本上使用组件x/y对齐来确定应该如何最好地放置各个组件

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.io.File;
import java.io.IOException;
import javax.imageio.ImageIO;
import javax.swing.ImageIcon;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;
import javax.swing.OverlayLayout;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;
import javax.swing.border.LineBorder;

public class OverlayLabel {

    public static void main(String[] args) {
        new OverlayLabel();
    }

    public OverlayLabel() {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                try {
                    try {
                        UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
                    } catch (ClassNotFoundException | InstantiationException | IllegalAccessException | UnsupportedLookAndFeelException ex) {
                        ex.printStackTrace();
                    }

                    JLabel background = new JLabel(new ImageIcon(ImageIO.read(new File("/path/to/image"))));
                    background.setAlignmentX(0.5f);
                    background.setAlignmentY(0.5f);

                    JFrame frame = new JFrame("Testing");
                    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                    frame.setLayout(new OverlayLayout(frame.getContentPane()));
                    frame.add(new TestPane());
                    frame.add(background);
                    frame.pack();
                    frame.setLocationRelativeTo(null);
                    frame.setVisible(true);
                } catch (IOException ex) {
                    ex.printStackTrace();
                }
            }
        });
    }

    public class TestPane extends JPanel {

        public TestPane() {
            setOpaque(false);
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(200, 200);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics g2d = (Graphics2D) g.create();
            int x = (getWidth() - 20) / 2;
            int y = (getHeight() - 20) / 2;
            g2d.setColor(Color.RED);
            g2d.fillRect(x, y, 20, 20);
            g2d.dispose();
        }

    }

}

最后,如果这些都不适合您,您可以使用它JLayeredPane作为基础,这将允许您确定每个组件的z顺序...

有关详细信息,请参见如何使用分层窗格 ...