Question

我有一个JFrame，在BorderLayout中包含2个JPanel子类和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。

不是显示我绘制的内容，而是将“JFrame的内容”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();
    }
}

screenshot

Answer 1

如果没有super.paintComponent(g)，则结果取决于您的平台JPanel UI委托PanelUI属性的默认值true。我的情况恰好是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.NORTH); this.add(control, BorderLayout.WEST); this.add(display, BorderLayout.CENTER); this.add(state, 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, yco, getWidth() / 2, getHeight() / 2); } }，但你可以在你的平台上进行试验，如下所示。

附录：“如果你不尊重opacity，你可能会看到视觉opaque property。” - artifacts。您观察到的paintComponent()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。

Main

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JPanel重绘问题

1 个答案: