如何动态调整JFrame的大小以包含具有不同内容大小的JPanel？

Question

如何使我的JFrame与容纳动态大小的内容的JPanel的大小匹配？

如果有人可以指导我通过它们，我已经创建了两个简单的课堂摘录。

类别1：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();
  }
}

电流输出

预期产量：

我知道类似的问题可能已经被问过很多次了，但我进行了仔细的搜索，无法获得明确的解决方案。 任何帮助表示赞赏。

Answer 1

您的JPanelEx将需要提供尺寸提示，以允许布局管理系统确定应如何最好地布置组件以及内容所需的空间量。

另外，不要在未创建的Graphics上下文上调用dispose ！

举个例子...

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();
            }
        }
    }

}

另请参阅在容器中布置组件以获取有关布局管理器API的更多详细信息