如何動態調整JFrame的大小以包含具有不同內容大小的JPanel？

Question

如何使我的JFrame與容納動態大小的內容的JPanel的大小匹配？

如果有人可以指導我通過它們，我已經創建了兩個簡單的課堂摘錄。

類別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類：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();
  }
}

電流輸出

預期產量：

我知道類似的問題可能已經被問過很多次了，但我進行了仔細的搜索，無法獲得明確的解決方案。 任何幫助表示贊賞。

Answer 1

您的JPanelEx將需要提供尺寸提示，以允許布局管理系統確定應如何最好地布置組件以及內容所需的空間量。

另外，不要在未創建的Graphics上下文上調用dispose ！

舉個例子...

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();
            }
        }
    }

}

另請參閱在容器中布置組件以獲取有關布局管理器API的更多詳細信息