如何动态调整JFrame的大小以包含具有不同内容大小的JPanel？

Question

如何使JFrame匹配与保存动态大小内容的JPanel的大小相匹配？

我创建了两个简单的类片段，如果有人可以指导我完成它们。

Class1：CanvasExample.java

import java.awt.Dimension;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;
public class CanvasExample {
    public static void main(String[] args) {
        JPanelEx dataOut = new JPanelEx();
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                JFrame f = new JFrame("Title!");
                f.setMinimumSize(new Dimension(200,100));
                f.getContentPane().add(dataOut);
                f.pack();
                f.setVisible(true);
            }
        });
    }
}

第2类：JPanelEx.java

import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.SwingUtilities;

public class JPanelEx extends JPanel {
   public JPanelEx() {
         super(new FlowLayout());
   }
   public void paintComponent(Graphics g) {
        super.paintComponent(g); 
        g.drawString("Hello1", 10, 10);
        g.drawString("Hello2", 10, 30);
        g.drawString("Hello3", 10, 50);
        g.drawString("Hello4", 10, 70);
        g.drawString("Hello5", 10, 90);
        g.drawString("Hello6", 10, 110);
        g.drawString("Hello7", 10, 130);
        g.drawString("Hello8", 10, 150);
        g.drawString("Hello9", 10, 170);
        g.drawString("Hello10", 10, 190);
        g.dispose();
  }
}

当前输出：

预期产出：

我理解类似的问题可能已被多次询问，但我扫描完毕并无法得到明确的解决方案。任何帮助表示赞赏。

Answer 1

您的JPanelEx需要提供大小提示，以便布局管理系统确定应该如何布置组件以及内容所需的空间量

另外，请勿在您未创建的dispose个上下文中致电Graphics！

作为一个例子......

import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.FlowLayout;
import java.awt.FontMetrics;
import java.awt.Graphics;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.UIManager;
import javax.swing.UnsupportedLookAndFeelException;

public class Test {

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

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

                JFrame frame = new JFrame("Testing");
                frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
                frame.add(new JPanelEx());
                frame.pack();
                frame.setLocationRelativeTo(null);
                frame.setVisible(true);
            }
        });
    }

    public class JPanelEx extends JPanel {

        private int numElements = 10;

        public JPanelEx() {
            super(new FlowLayout());
        }

        @Override
        public Dimension getPreferredSize() {

            FontMetrics fm = getFontMetrics(getFont());
            int width = 0;
            int height = fm.getHeight() * numElements;
            for (int index = 0; index < numElements; index++) {
                width = Math.max(width, fm.stringWidth("Hello" + index));
            }

            return new Dimension(width, height);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            int x = 0;
            int y = 0;
            FontMetrics fm = g.getFontMetrics();
            for (int index = 0; index < numElements; index++) {
                g.drawString("Hello" + index, x, y + fm.getAscent());
                y += fm.getHeight();
            }
        }
    }

}

有关布局管理器API

的更多详细信息，另请参阅Laying Out Components Within a Container