java – JPanel重绘问题

发布时间：2020-12-14 05:56:36 所属栏目：Java 来源：网络整理

导读：我有一个JFrame,其中包含2个JPanel子类和BorderLayout中的2个JLabel.其中一个JPanel包含JButtons,另一个用于显示图形. JLabels位于北部和南部,西部是JPanel按钮,中间是JPanel. 显示JPanel需要不断刷新,所以我通过swing计时器生成的动作事件调用它的repaint()

我有一个JFrame,其中包含2个JPanel子类和BorderLayout中的2个JLabel.其中一个JPanel包含JButtons,另一个用于显示图形. JLabels位于北部和南部,西部是JPanel按钮,中间是JPanel.

显示JPanel需要不断刷新,所以我通过swing计时器生成的动作事件调用它的repaint()方法.我也覆盖它的paintComponent()方法来做我的绘图.

而不是显示我绘制的内容,“JFrame的内容”被绘制到显示JPanel上.我知道在完成绘图之前,我可以通过使用g.fillRect()或super.paintComponent()简单地“清除”显示JPanel.

我只是好奇为什么会这样.

我正在使用jdk 1.6u27.下面是我的代码：

package test;

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

public class Main {

public static void main(String[] args) {
    Simulation sim = new Simulation();

    }
}

class Simulation extends JFrame {

    public JLabel state;
    private JLabel id;
    private ButtonPanel control;
    private Display display;

    public Simulation() {
        id = new JLabel("Test");
        state = new JLabel("Test");
        control = new ButtonPanel();
        display = new Display(this);

        this.setLayout(new BorderLayout());
        this.add(id,BorderLayout.NORTH);
        this.add(control,BorderLayout.WEST);
        this.add(display,BorderLayout.CENTER);
        this.add(state,BorderLayout.SOUTH);

        this.setSize(500,600);
        this.setVisible(true);
        this.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);

    }

    public ButtonPanel getControl() {
        return this.control;
    }
}

class ButtonPanel extends JPanel implements ActionListener {

    public JButton b[] = new JButton[8];
    public boolean bp[] = new boolean[8];

    public ButtonPanel() {
        this.setLayout(new GridLayout(8,1));

        for (int i = 0; i < b.length; i++) {
            b[i] = new JButton(""+i);
            b[i].addActionListener(this);
            bp[i] = false;
            this.add(b[i]);
        }
    }

    public void actionPerformed(ActionEvent e) {
        //do something
    }
}

class Display extends JPanel implements ActionListener {

    private Timer tm;
    private int yco;
    private Simulation sim;

    public Display(Simulation sim) {
        tm = new Timer(100,this);
        tm.start();

        yco = 0;

        this.sim = sim;
    }

    @Override
    public void paintComponent(Graphics g) {
        //draw something
        g.drawLine(0,yco,100,100);
    }

    public void actionPerformed(ActionEvent e) {
        yco ++;
        this.repaint();
    }
}

解决方法

如果没有super.paintComponent(g),结果将取决于您的平台JPanel UI委托,PanelUI的 opacity属性的默认值.我的情况恰好如此,但您可以在您的平台上进行试验,如下所示.

附录：“如果你不尊重opaque property,你可能会看到视觉artifacts.” – paintComponent().您观察到的artifact会因平台而异,但并非典型.实际上,你违背了绘制每个像素的承诺,你会看到在某个缓冲区中遗留下来的东西.

import java.awt.*;
import java.awt.event.*;
import java.util.ArrayList;
import java.util.List;
import javax.swing.*;

public class Main {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {

            @Override
            public void run() {
                Simulation sim = new Simulation();
            }
        });
    }
}

class Simulation extends JFrame {

    public JCheckBox state;
    private JLabel id;
    private ButtonPanel control;
    private Display display;

    public Simulation() {
        id = new JLabel("Test");
        state = new JCheckBox("Opaque");
        control = new ButtonPanel();
        display = new Display(this);

        this.setLayout(new BorderLayout());
        this.add(id,BorderLayout.SOUTH);
        state.addItemListener(new ItemListener() {

            @Override
            public void itemStateChanged(ItemEvent e) {
                display.setOpaque(e.getStateChange() == ItemEvent.SELECTED);
            }
        });
        state.setSelected(true);

        this.pack();
        this.setVisible(true);
        this.setDefaultCloSEOperation(JFrame.EXIT_ON_CLOSE);
    }

    public ButtonPanel getControl() {
        return this.control;
    }
}

class ButtonPanel extends JPanel {

    private static final int N = 8;
    private List<JToggleButton> list = new ArrayList<JToggleButton>(N);

    public ButtonPanel() {
        this.setLayout(new GridLayout(0,1));
        for (int i = 0; i < N; i++) {
            final JToggleButton b = new JToggleButton(String.valueOf(i));
            b.addActionListener(new ActionListener() {

                @Override
                public void actionPerformed(ActionEvent e) {
                    //System.out.println(b.isSelected());
                }
            });
            list.add(b);
            this.add(b);
        }
    }
}

class Display extends JPanel {

    private Simulation sim;
    private Timer tm;
    private int yco;

    public Display(Simulation sim) {
        this.setPreferredSize(new Dimension(320,320));
        this.setOpaque(true);
        this.sim = sim;
        tm = new Timer(100,new ActionListener() {

            @Override
            public void actionPerformed(ActionEvent e) {
                yco++;
                repaint();
            }
        });
        tm.start();
    }

    @Override
    public void paintComponent(Graphics g) {
        //super.paintComponent(g);
        g.drawLine(0,getWidth() / 2,getHeight() / 2);
    }
}

（编辑：李大同）

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