Question

我是非常新的Java，对任何愚蠢的问题都很抱歉。

这是我的问题：

我只想绘制一条线 - 如果我将JLabel Myline()直接添加到label作为JFrame MyFrame，那么它将显示在JFrame中MyLine() 1}} - Dialogwindow，但是如果我将JPanel添加到panel panel和MyFrame添加到package examples; import java.awt.Color; import java.awt.Dimension; import java.awt.Font; import java.awt.Graphics; import java.awt.GridBagLayout; import java.awt.GridLayout; import java.awt.Toolkit; import java.awt.image.BufferedImage; import java.io.IOException; import javax.imageio.ImageIO; import javax.swing.BorderFactory; import javax.swing.JButton; import javax.swing.JComponent; import javax.swing.JFrame; import javax.swing.JLabel; import javax.swing.JPanel; import javax.swing.border.EtchedBorder; import javax.swing.border.TitledBorder; public class Bsp { public static void main(String[] args) { JFrame frame = new MyFrame(); } } class MyFrame extends JFrame { private class MyLine extends JLabel { int width; public MyLine(int width) { this.width=width; } @Override protected void paintComponent(Graphics g) { super.paintComponent(g); g.setColor(Color.BLACK); g.drawLine(0, 0, getWidth(), 0); g.dispose(); } } public MyFrame() { JLabel label=new MyLine(getWidth()); JPanel panel=new JPanel(new GridBagLayout()); setLocationRelativeTo(null); setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE); setLayout(new GridLayout(3, 1)); panel.add(label); add(new JButton("A")); add(new JButton("B")); add(panel); pack(); setVisible(true); } }，那么就没有Line。

为什么？

{{1}}

Answer 1

在MyFrame询问所包含组件的首选大小之前，

pack()没有首选大小。给MyLine一个首选大小以查看效果。另请参阅Initial Threads。

import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JLabel;
import javax.swing.JPanel;

public class Bsp {

    public static void main(String[] args) {
        JFrame frame = new MyFrame();
    }
}

class MyFrame extends JFrame {

    private class MyLine extends JLabel {

        int width;

        public MyLine(int width) {
            this.width = width;
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(Color.BLACK);
            g.drawLine(0, 0, getWidth(), getHeight());
            g.dispose();
        }

        @Override
        public Dimension getPreferredSize() {
            return new Dimension(width, 16);
        }

    }

    public MyFrame() {

        JLabel label = new MyLine(32);
        System.out.println(getWidth());
        JPanel panel = new JPanel(new GridBagLayout());

        setLocationRelativeTo(null);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLayout(new GridLayout(3, 1));

        panel.add(label);

        add(new JButton("A"));
        add(new JButton("B"));
        add(panel);
        pack();
        setVisible(true);

    }
}

在JLabel中绘制线并在JFrame中添加为JPanel不起作用

1 个答案: