java - 图形未出现在 CardLayout 上

Question

我正在构建一个使用 CardLayout 在屏幕之间切换的 GUI。我希望其中一个屏幕上有图形。我已经成功地能够使用 GridLayout 将矩形放在面板上，然后将该面板放在主面板上，并且矩形清晰可见。但是，当我将该面板放到 CardLayout 面板上时，矩形就看不到了。将图形添加到 CardLayout 面板时是否需要做一些不同的事情？

主类

import java.awt.CardLayout;
import java.awt.Container;
import javax.swing.JPanel;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JTextField;
import java.awt.GridBagLayout;
import java.awt.GridBagConstraints;
import javax.swing.JLabel;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;
import java.awt.Dimension;

public class Window extends JFrame {
    public Window() {
        // Main Panel Configuration
        Container panel = this.getContentPane();
        panel.setLayout(new GridBagLayout());
        panel.setSize(1000,1000);
        GridBagConstraints gbc = new GridBagConstraints();

        // GridBag Constraints
        gbc.fill = GridBagConstraints.HORIZONTAL;
        gbc.gridheight = 1;
        gbc.weightx = 1;
        gbc.weighty = 1;
        gbc.gridx = 0;
        gbc.gridy = 0;

        // Button Tabs
        JButton button1 = new JButton("button 1");
        panel.add(button1, gbc);

        JButton button2 = new JButton("button 2");
        gbc.gridx = 1;
        panel.add(button2, gbc);

        // Panels for CardLayout
        JPanel panel1 = new JPanel();
        JPanel panel2 = new JPanel();

        // Set Layout of Panels
        panel1.setLayout(new GridBagLayout());
        panel2.setLayout(new GridBagLayout());

        // Set Dimensions of Panels
        panel1.setSize(new Dimension(900, 500));
        panel2.setSize(new Dimension(900, 500));

        // Labels for panels
        JLabel label1 = new JLabel("label 1");
        gbc.gridx = 1;
        gbc.gridy = 2;
        panel1.add(label1, gbc);

        JLabel label2 = new JLabel("label 2");
        gbc.gridy = 2;
        panel2.add(label2, gbc);

        // TextFields for Panels
        JTextField textField1 = new JTextField();
        gbc.gridx = 2;
        gbc.gridy = 2;
        panel1.add(textField1, gbc);

        JTextField textField2 = new JTextField();
        gbc.gridy = 2;
        panel2.add(textField2, gbc);


        // Add Graphic to panel1
        JPanel drawingPanel = new JPanel();
        DrawingComponent dc = new DrawingComponent();
        dc.setPreferredSize(new Dimension(100, 100));
        drawingPanel.add(dc);
        gbc.gridx = 0;
        gbc.gridy = 3;
        panel1.add(drawingPanel,gbc);


        // Set TextField Dimensions
        textField1.setPreferredSize(new Dimension(400, 20));
        textField2.setPreferredSize(new Dimension(400, 20));

        // CardLayout Panel for Entry Fields and Labels
        JPanel cardLayoutPanel = new JPanel();
        CardLayout c1 = new CardLayout();
        cardLayoutPanel.setLayout(c1);
        cardLayoutPanel.setSize(new Dimension(900, 600));

        // Add Panels to CardLayout Panel
        cardLayoutPanel.add("panel1",panel1);
        cardLayoutPanel.add("panel2", panel2);

        // Which panel to show First
        c1.show(cardLayoutPanel, "panel1");

        // Add CardLayout Panel to Main Panel
        gbc.gridy = 1;
        gbc.gridx = 0;
        panel.add(cardLayoutPanel, gbc);


        // Action Listeners Changing Between Tabs
        button1.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent arg0) {
                c1.show(cardLayoutPanel, "panel1");
            }
        });


        button2.addActionListener(new ActionListener(){
            public void actionPerformed(ActionEvent arg0) {
                c1.show(cardLayoutPanel, "panel2");
            }
        });

        setSize(800,600);
        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setVisible(true);

    }


    public static void main(String[] args){
        Window window = new Window();

    }
}

绘图组件类

import java.awt.Graphics;
import java.awt.Graphics2D;
import javax.swing.JComponent;
import java.awt.Rectangle;

public class DrawingComponent extends JComponent {
    public void paintComponent(Graphics g){
        Graphics2D g2 = (Graphics2D) g;

        Rectangle rect1 = new Rectangle(400, 400, 50, 50);
        g2.draw(rect1);
    }
}

Answer 1

在这一部分:

JPanel drawingPanel = new JPanel();
DrawingComponent dc = new DrawingComponent();
dc.setPreferredSize(new Dimension(100, 100));
drawingPanel.add(dc);

您设置 DrawingComponent 的首选大小至(100,100)。然后，当您绘制组件时，您将在 Rectangle(400, 400, 50, 50) 中绘制矩形。使用构造函数Rectangle(int x, int y, int width, int height) .

话虽如此，我认为这是非常明显的。您的组件为 100x100，但您尝试在第 400x400 个像素处绘制，这会导致在组件边界之外绘制矩形。

我不知道矩形的坐标应该是什么，但如果您希望显示组件，请将矩形更改为 Rectangle rect1 = new Rectangle(0, 0, 50, 50);

此外，VGR 在评论中提到(他明白了我:P)当你 override 时paintComponent方法，请确保您调用 super.paintComponent() .

最后，使用 SwingUtilities#invokeLater 启动您的应用程序方法。

我在代码中的意思的总和:

public static class DrawingComponent extends JComponent {
        public void paintComponent(Graphics g) {
            super.paintComponent(g); // Should always start with super method.
            Graphics2D g2 = (Graphics2D) g;

            Rectangle rect1 = new Rectangle(0, 0, 50, 50);
            g2.draw(rect1);
        }
    }

    public static void main(String[] args) {
        // All swing applications must run on their own thread named EDT (Event dispatch thread)
        SwingUtilities.invokeLater(() -> {
            Window window = new Window();
        });
    }