如何实现图形到JScrollPane？

Question

objective 是在 window 上绘制几十万条垂直线，因此我需要一个滚动条，缩小不是一个选项，因为 space分隔每条线甚至不是一个像素。我采用了在 class 中使用绘画方法并将 class 和 JScrollPane 添加到 JFrame 的方法。没有解决这就是为什么我采用使用 NetBeans JFrame 表单的方法。基本上，我如何将我的图形方法实现到具有滚动条的面板中？我遇到的问题是我的值在打印机上很好，但根本没有 window 出现。如果需要任何其他信息，请告诉我。谢谢

public class PedroGUI extends javax.swing.JFrame {
    public PedroGUI() {
        initComponents();
        draw();
    }
    @SuppressWarnings("unchecked")
    // <editor-fold defaultstate="collapsed" desc="Generated Code">                          
    private void initComponents() {

        scroll = new javax.swing.JScrollPane();

        setDefaultCloseOperation(javax.swing.WindowConstants.EXIT_ON_CLOSE);

        scroll.setHorizontalScrollBarPolicy(javax.swing.ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);
        scroll.setVerticalScrollBarPolicy(javax.swing.ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);

        javax.swing.GroupLayout layout = new javax.swing.GroupLayout(getContentPane());
        getContentPane().setLayout(layout);
        layout.setHorizontalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(scroll, javax.swing.GroupLayout.PREFERRED_SIZE, 429, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(123, Short.MAX_VALUE))
        );
        layout.setVerticalGroup(
            layout.createParallelGroup(javax.swing.GroupLayout.Alignment.LEADING)
            .addGroup(layout.createSequentialGroup()
                .addContainerGap()
                .addComponent(scroll, javax.swing.GroupLayout.PREFERRED_SIZE, 267, javax.swing.GroupLayout.PREFERRED_SIZE)
                .addContainerGap(86, Short.MAX_VALUE))
        );

        pack();
    }// </editor-fold>                        


    public void draw() {
        Graphics g = scroll.getGraphics();
        g.setColor(Color.red);
        int bytes, samples, frequency;
        try {
            FileInputStream fis = new FileInputStream("./pepe.wav");
            BufferedInputStream bis = new BufferedInputStream(fis);
            byte[] data = new byte[128];
            bis.skip(44);
            samples = 0;
            while ((bytes = bis.read(data)) > 0) {
                for (int i = 0; i < bytes; i++) {
                    frequency = data[i] & 0xFF; 
                    System.out.println(samples + " " + frequency);
                    g.drawLine(samples, frequency + 300, samples, -frequency + 300);
                    samples++;
                }

            }
            bis.read(data);
            bis.close();
        } catch (Exception e) {
            e.printStackTrace();
        }
    }

    public static void main(String args[]) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                PedroGUI a = new PedroGUI();
                a.draw();
            }
        });
    }

    private javax.swing.JScrollPane scroll;

}

Answer 1

绘画通常是通过覆盖基于 JComponent 的 class 的 paintComponent 来实现的。您不想做的是尝试覆盖 JScrollPane 的 paint/paintComponent 并且肯定不会使用 getGraphics.

getGraphics returns 绘制到组件的最后一个东西的快照，如果你尝试绘制到这个，它将在下次绘制组件时被丢弃，因为 Swing使用被动渲染算法，这可能会立即或在将来的某个随机时间完成（这就是为什么你应该使用 paintComponent）

绘制也是破坏性的，也就是说，你应该从头开始重新绘制组件的状态。

JScrollPane也是一个复合组件，也就是说，还有一些其他的组件用来实现它的功能（即JViewport）

您可能应该做的是创建一个自定义组件，从类似 JPanel 的东西扩展，并覆盖它的 paintComponent 方法并从中生成您的图表。

此示例还使用了 Scrollable 接口，它允许 JScrollPane 最初的布局小于组件的首选大小，这很好，因为组件可能是很宽。

这个例子也只是生成一个简单的直方图，但你明白了要点

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.EventQueue;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.Rectangle;
import java.awt.geom.Rectangle2D;
import java.util.Map;
import java.util.TreeMap;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.Scrollable;

public class Main {

    public static void main(String[] args) {
        EventQueue.invokeLater(new Runnable() {
            @Override
            public void run() {
                new Main();
            }
        });
    }

    public Main() {
        // For this example, I just randomised some data, you would
        // Need to load it yourself...
        int width = 256;
        int height = 256;
        int[][] data = new int[width][height];
        for (int c = 0; c < height; c++) {
            for (int r = 0; r < width; r++) {
                data[c][r] = (int) (256 * Math.random());
            }
        }
        Map<Integer, Integer> mapHistory = new TreeMap<Integer, Integer>();
        for (int c = 0; c < data.length; c++) {
            for (int r = 0; r < data[c].length; r++) {
                int value = data[c][r];
                int amount = 0;
                if (mapHistory.containsKey(value)) {
                    amount = mapHistory.get(value);
                    amount++;
                } else {
                    amount = 1;
                }
                mapHistory.put(value, amount);
            }
        }
        JFrame frame = new JFrame("Test");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setLayout(new BorderLayout());
        frame.add(new JScrollPane(new Graph(mapHistory)));
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    protected class Graph extends JPanel implements Scrollable {

        protected static final int MIN_BAR_WIDTH = 4;
        private Map<Integer, Integer> mapHistory;

        public Graph(Map<Integer, Integer> mapHistory) {
            this.mapHistory = mapHistory;
        }

        @Override
        public Dimension getPreferredSize() {
            int width = (mapHistory.size() * MIN_BAR_WIDTH) + 11;
            return new Dimension(width, 256);
        }

        @Override
        public Dimension getMinimumSize() {
            int width = (mapHistory.size() * MIN_BAR_WIDTH) + 11;
            return new Dimension(width, 128);
        }

        @Override
        protected void paintComponent(Graphics g) {
            super.paintComponent(g);
            if (mapHistory != null) {
                int xOffset = 5;
                int yOffset = 5;
                int width = getWidth() - 1 - (xOffset * 2);
                int height = getHeight() - 1 - (yOffset * 2);
                Graphics2D g2d = (Graphics2D) g.create();
                g2d.setColor(Color.DARK_GRAY);
                g2d.drawRect(xOffset, yOffset, width, height);
                int barWidth = Math.max(MIN_BAR_WIDTH,
                                (int) Math.floor((float) width
                                                / (float) mapHistory.size()));
                int maxValue = 0;
                for (Integer key : mapHistory.keySet()) {
                    int value = mapHistory.get(key);
                    maxValue = Math.max(maxValue, value);
                }
                int xPos = xOffset;
                for (Integer key : mapHistory.keySet()) {
                    int value = mapHistory.get(key);
                    int barHeight = Math.round(((float) value
                                    / (float) maxValue) * height);
                    g2d.setColor(new Color(key, key, key));
                    int yPos = height + yOffset - barHeight;
                    Rectangle2D bar = new Rectangle2D.Float(
                                    xPos, yPos, barWidth, barHeight);
                    g2d.fill(bar);
                    g2d.setColor(Color.DARK_GRAY);
                    g2d.draw(bar);
                    xPos += barWidth;
                }
                g2d.dispose();
            }
        }

        @Override
        public Dimension getPreferredScrollableViewportSize() {
            return new Dimension(512, 256);
        }

        @Override
        public int getScrollableUnitIncrement(Rectangle visibleRect, int orientation, int direction) {
            return 128;
        }

        @Override
        public int getScrollableBlockIncrement(Rectangle visibleRect, int orientation, int direction) {
            return 128;
        }

        @Override
        public boolean getScrollableTracksViewportWidth() {
            return getPreferredSize().width
                            <= getParent().getSize().width;
        }

        @Override
        public boolean getScrollableTracksViewportHeight() {
            return getPreferredSize().height
                            <= getParent().getSize().height;
        }
    }
}

有关详细信息，请参阅 Painting in AWT and Swing, Performing Custom Painting and How to Use Scroll Panes

如何实现图形到JScrollPane？

How to implement graphics to JScrollPane?

java

user-interface

swing

jframe

jscrollpane