java - 如何使用定时器动态调整帧大小？

Question

我正在尝试使用 Timer 对象动态调整窗口大小，但没有成功...我在构造函数中设置了面板的首选大小，这很好地设置了窗口的大小，尽管只有一次。程序初始化后首选大小会发生变化，但窗口大小保持不变。为什么？因为构造函数只初始化一次，因此不受大小变化的影响？如果是这样，我怎样才能解决这个问题以实时调整窗口大小？

我知道这不会解决开头评论中给出的练习中的问题，所以请忽略它:-)

/*
 * Exercise 18.15
 * 
 * "(Enlarge and shrink an image) Write an applet that will display a sequence of
 * image files in different sizes. Initially, the viewing area for this image has
 * a width of 300 and a height of 300. Your program should continuously shrink the
 * viewing area by 1 in width and 1 in height until it reaches a width of 50 and
 * a height of 50. At that point, the viewing area should continuously enlarge by 
 * 1 in width and 1 in height until it reaches a width of 300 and a height of 300. 
 * The viewing area should shrink and enlarge (alternately) to create animation
 * for the single image."
 * 
 * Created: 2014.01.07
 */



import javax.swing.*;
import java.awt.*;
import java.awt.event.*;


public class Ex_18_15 extends JApplet {


    // Main method
    public static void main(String[] args) {
        JFrame frame = new JFrame();
        Ex_18_15 applet = new Ex_18_15();
        applet.isStandalone = true;
        frame.add(applet);

        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }







    // Data fields

    private boolean isStandalone = false;

    private Image image = new ImageIcon("greenguy.png").getImage();

    private int xCoordinate = 360;
    private int yCoordinate = 300;

    private Timer timer = new Timer(20, new TimerListener());

    private DrawPanel panel = new DrawPanel();


    // Constructor
    public Ex_18_15() {
        panel.setPreferredSize(new Dimension(xCoordinate, yCoordinate));
        add(panel);

        timer.start();
    }



class DrawPanel extends JPanel {

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);

        g.drawImage(image, 0, 0, this);
    }
}



class TimerListener implements ActionListener {
    @Override
    public void actionPerformed(ActionEvent e) {
        if(yCoordinate <= 50) {
            yCoordinate++;
            xCoordinate++;
        }

        else if(yCoordinate >= 300) {
            yCoordinate--;
            xCoordinate--;
        }

        panel.setPreferredSize(new Dimension(xCoordinate, yCoordinate));
        repaint();
    }
}

}

Answer 1

您需要重新打包 JFrame 才能调整其大小。例如在 ActionListener 的末尾:

Window win = SwingUtilities.getWindowAncestor(panel);
win.pack();

但有一个问题要问你:为什么你的类扩展 JApplet 而不是 JPanel？或者如果它需要是一个小程序，为什么要把它塞到 JFrame 中？

<小时/>

编辑
关于您的评论:

Wouldn't it usually be extending JFrame not JPanel? I'm stuffing it into a JFrame to allow it to run as an application as well as an applet. That's how 'Introduction to Java Programming' tells me how to do it :p Adding your code at the end of the actionPerformed method didn't do anything for me ;o

您的大部分 GUI 代码应该用于创建 JPanel，而不是 JFrame 或 JApplet。然后，您可以毫无困难地将 JPanel 放置在需要的地方。您的书存在严重问题，如果它告诉您这一点，则不应信任。

<小时/>

编辑2
对我有用:

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;

@SuppressWarnings("serial")
public class ShrinkingGui extends JPanel {
   private static final int INIT_W = 400;
   private static final int INIT_H = INIT_W;
   private static final int TIMER_DELAY = 20;
   private int prefW = INIT_W;
   private int prefH = INIT_H;

   public ShrinkingGui() {
      new Timer(TIMER_DELAY, new TimerListener()).start();;
   }

   public Dimension getPreferredSize() {
      return new Dimension(prefW, prefH);
   }

   private class TimerListener implements ActionListener {
      @Override
      public void actionPerformed(ActionEvent e) {
         if (prefW > 0 && prefH > 0) {
            prefW--;
            prefH--;
            Window win = SwingUtilities.getWindowAncestor(ShrinkingGui.this);
            win.pack();
         } else {
            ((Timer)e.getSource()).stop();
         }
      }
   }

   private static void createAndShowGUI() {
      ShrinkingGui paintEg = new ShrinkingGui();

      JFrame frame = new JFrame("Shrinking Gui");
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
      frame.getContentPane().add(paintEg);
      frame.pack();
      frame.setLocationRelativeTo(null);
      frame.setVisible(true);
   }

   public static void main(String[] args) {
      SwingUtilities.invokeLater(new Runnable() {
         public void run() {
            createAndShowGUI();
         }
      });
   }
}