Question

我正在尝试在JScrollPane中显示一堆ImagePanel。此应用程序的问题在于，每当新的面板行进入视口时，整个窗口就会冻结一小段时间。但是，一旦滚动到末尾，该窗口将不再滞后。

造成这种滞后的原因是什么？我该如何防止它首先发生？

我的猜测是，直到将面板滚动到面板时，它们才会被绘画。所以我尝试在将它们添加到背景后对它们进行重绘，但这不起作用：（

MainClass.java：

import javax.swing.SwingUtilities;

public class MainClass {

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

MainFrame.java：

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

public class MainFrame extends JFrame {

    private static final long serialVersionUID = -254980289568295701L;

    public MainFrame() {

        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setExtendedState(JFrame.MAXIMIZED_BOTH);

        JPanel background = new JPanel();
        JScrollPane scrollPane = new JScrollPane(background,
                 JScrollPane.VERTICAL_SCROLLBAR_AS_NEEDED,
                 JScrollPane.HORIZONTAL_SCROLLBAR_NEVER);
        ImagePanel ipanel;

        background.setPreferredSize(new Dimension(this.getWidth(),
                                              this.getHeight() + 3000));    

        scrollPane.setOpaque(false);
        scrollPane.getViewport().setOpaque(false);
        scrollPane.getVerticalScrollBar().setUnitIncrement(20);
        add(scrollPane);

        for (int i = 0; i < 40; i++) {
            ipanel = new ImagePanel();
            ipanel.setPreferredSize(new Dimension(300, 400));
            ipanel.setSize(new Dimension(300, 400));

            background.add(ipanel);
        }

        setVisible(true);
    }
}

ImagePanel.java：

import java.awt.*;
import javax.swing.JPanel;
import java.awt.image.BufferedImage;

public class ImagePanel extends JPanel {

    private static final long serialVersionUID = 1997246878999790104L;
    private Image image;
    private int width;
    private int height;

    public ImagePanel() {
    width = 300;
    height = 400;
    BufferedImage bufferedImage = new BufferedImage(2000, 2000, BufferedImage.TYPE_INT_RGB);
    Graphics2D g2d = bufferedImage.createGraphics();
    g2d.setColor(Color.white);
    g2d.fillRect(0, 0, 2000, 2000);
    g2d.setColor(Color.black);
    g2d.fillOval(0, 0, 2000, 2000);
    g2d.setColor(Color.yellow);
    g2d.fillOval(1500, 300, 400, 400);
    g2d.fillOval(1200, 600, 400, 400);
    g2d.fillOval(900, 900, 400, 400);
    g2d.fillOval(600, 1200, 400, 400);
    g2d.fillOval(300, 1500, 400, 400);
    g2d.dispose();
    image = bufferedImage.getScaledInstance(width, height, Image.SCALE_SMOOTH);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.drawImage(image, 0, 0, this);
    }
}

Answer 1

我将您的代码更改为JLabel，以显示图片。

加载时间更长，但滚动效果很好：

import java.awt.*;
import javax.swing.*;
import java.awt.image.BufferedImage;

//public class ImagePanel extends JPanel {
public class ImagePanel extends JLabel {

    private static final long serialVersionUID = 1997246878999790104L;
    private Image image;
    private int width;
    private int height;

    public ImagePanel() {
    width = 300;
    height = 400;
    BufferedImage bufferedImage = new BufferedImage(2000, 2000, BufferedImage.TYPE_INT_RGB);
    Graphics2D g2d = bufferedImage.createGraphics();
    g2d.setColor(Color.white);
    g2d.fillRect(0, 0, 2000, 2000);
    g2d.setColor(Color.black);
    g2d.fillOval(0, 0, 2000, 2000);
    g2d.setColor(Color.yellow);
    g2d.fillOval(1500, 300, 400, 400);
    g2d.fillOval(1200, 600, 400, 400);
    g2d.fillOval(900, 900, 400, 400);
    g2d.fillOval(600, 1200, 400, 400);
    g2d.fillOval(300, 1500, 400, 400);
    g2d.dispose();
    image = bufferedImage.getScaledInstance(width, height, Image.SCALE_SMOOTH);
    setIcon( new ImageIcon(image) );
    }

//    @Override
    protected void xxxpaintComponent(Graphics g) {
        super.paintComponent(g);
//        g.drawImage(image, 0, 0, this);
        g.drawImage(image, 0, 0, null);
    }
}

使用JScrollPane首次显示图像时的延迟窗口

1 个答案: