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java - 首次使用 JScrollPane 显示图像时窗口滞后

问题描述

我正在尝试在 JScrollPane 中显示一堆 ImagePanel。这个应用程序的问题是每次新的一行面板进入视口时，整个窗口都会冻结一小段时间。但是，一旦滚动到最后，窗口将不会再次滞后。

这种滞后的原因是什么？我如何从一开始就防止它发生？

我的猜测是面板在滚动到之前不会被绘制。所以我尝试在将它们添加到背景后对它们调用重绘，但这不起作用:(

主类.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);
    }
}

标签： javaimageperformanceswingjscrollpane

解决方案

我将您的代码更改为我们 aJLabel以显示图像。

加载需要更长的时间，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);
    }
}

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