java - 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。

类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);
            }
        });
    }
}

类2: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:

预期输出:

我知道类似的问题可能已经被问过很多次了，但我浏览了一下，但找不到明确的解决方案。任何帮助表示赞赏。

Answer 1

您的JPanelEx将需要提供大小提示，以允许布局管理系统确定组件的最佳布局方式以及内容所需的空间量

此外，请勿对您未创建的 Graphics 上下文调用 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Laying Out Components Within a Container有关布局管理器 API 的更多详细信息