java - 在Java中制作一条数轴来显示一个点，getWidth()和getHeight()没有正确校准位置

Question

所以我想创建一个数轴类，我可以用它来显示沿单个轴的单个点，但我希望它能够响应当前所在容器的大小，并相对于该容器更改其大小。不幸的是，我无法正确使用 getWidth() 和 getHeight() 来获取我想要的数轴。这是我到目前为止编写的代码:

import javax.swing.*;
import java.awt.*;
import java.awt.geom.Ellipse2D;
import java.awt.geom.Line2D;

public class NumberLine extends JPanel {
    private int value;
    private Color green1 = new Color(32, 77, 2);

@Override
public void paintComponent(Graphics g)
{
    Graphics2D g2 = (Graphics2D) g;
    int maxXValue = getWidth();
    int maxYValue = getHeight();
    Line2D.Float xline = new Line2D.Float((float) maxXValue/6, (float) maxYValue/2, (float) maxXValue * (5/6), (float) maxYValue/2);
    Line2D.Float yline = new Line2D.Float( (float) maxXValue/ 2, (float) maxYValue * (9/20), (float) maxXValue/2, (float) maxYValue *(11/20));
    g2.draw(xline);
    g2.draw(yline);
    Ellipse2D.Float cir = new Ellipse2D.Float((float) (maxXValue/10 + (8 * value/1000) * (maxXValue)), (float) (maxYValue/2), 10F, 10F );
    g2.setColor(green1);
    g2.fill(cir);
}


public NumberLine(int val0) {
    value = val0;
}

public static void main(String[] args) {
    JFrame frame = new JFrame();
    frame.setSize(150,100);
    NumberLine num = new NumberLine(5);
    frame.setContentPane(num);
    frame.setVisible(true);

}
}

理想情况下，我想要这样的事情，如果我要做的话

NumberLine num = new NumberLine(5);

我会得到看起来像这样的东西:

相反，我得到:

Answer 1

我认为你的问题是基本几何问题之一。如果您尝试将圆置于直线的中心，则需要从其位置减去其宽度和高度的一半。就是这样:

Ellipse2D.Float cir = new Ellipse2D.Float(
        (float) (maxXValue / 10 + (8 * value / 1000) * (maxXValue)) - 5,
        (float) (maxYValue / 2) - 5, 10F, 10F);

此外，您正在进行 int 除法，这会在您不需要的地方返回 0 值。改变

Line2D.Float yline = new Line2D.Float((float) maxXValue / 2, (float) maxYValue * (9 / 20),
        (float) maxXValue / 2, (float) maxYValue * (11 / 20));

到

Line2D.Float yline = new Line2D.Float((float) maxXValue / 2, (float) maxYValue * (9f / 20f),
        (float) maxXValue / 2f, (float) maxYValue * (11f / 20f));

不相关的问题:

• 不要忘记调用 super 组件的paintComponent方法:

  @Override
  public void paintComponent(Graphics g) {
      super.paintComponent(g); // !! don't forget this!
  

• 并避免在程序中使用“魔法”数字，因为它们会使调试变得困难。

• 使用 RenderingHints 平滑您的 Graphics2D 绘图:

  // rendering hints to smooth out your drawing
  g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, 
       RenderingHints.VALUE_ANTIALIAS_ON);
  

• 在 EDT 上启动 Swing GUI:

  SwingUtilities.invokeLater(() -> {
      JFrame frame = new JFrame();
      frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
  

例如，类似:

import java.awt.BasicStroke;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Graphics;
import java.awt.Graphics2D;
import java.awt.RenderingHints;
import java.awt.Stroke;
import javax.swing.JPanel;

public @SuppressWarnings("serial")
class NumberLine3 extends JPanel {
    private static final double X_GAP = 1.0 / 20.0;
    private static final double MAJOR_TIC_HT = 0.4;
    private static final int PREF_W = 600;
    private static final int PREF_H = 50;
    private static final Stroke MAIN_STROKE = new BasicStroke(5f);
    private static final Stroke MAJOR_TIC_STOKE = new BasicStroke(3f);
    private static final int CIRCLE_WIDTH = 20;
    private static final Color VALUE_COLOR = new Color(32, 230, 2);
    private int maxX;
    private int majorTickCount;
    private int minorTicksPerMajor;
    private double value;

    public NumberLine3(int maxX, int majorTickCount, int minorTicksPerMajor, double value) {
        this.maxX = maxX;
        this.majorTickCount = majorTickCount;
        this.minorTicksPerMajor = minorTicksPerMajor;
        this.value = value;
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        Graphics2D g2 = (Graphics2D) g;

        // rendering hints to smooth out your drawing
        g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);

        Graphics2D g2b = (Graphics2D) g2.create(); // so we can change stroke without problems
        g2b.setStroke(MAIN_STROKE);
        int x1 = (int) xValueToScreen(-maxX);
        int y1 = getHeight() / 2;
        int x2 = (int) xValueToScreen(maxX);
        int y2 = y1;
        g2b.drawLine(x1, y1, x2, y2);
        g2b.setStroke(MAJOR_TIC_STOKE);
        for (int i = 0; i <= 2 * majorTickCount; i++) {
            double xVal = ((double) i * maxX) / majorTickCount - maxX;
            x1 = (int) xValueToScreen(xVal);
            x2 = x1;
            double dY1 = getHeight() * (1 - MAJOR_TIC_HT) / 2.0;
            if (i == majorTickCount) {
                dY1 = 0.5 * dY1;
            }
            double dY2 = getHeight() - dY1;
            g2b.drawLine(x1, (int) dY1, x2, (int) dY2);
        }
        g2b.dispose();

        g2.setColor(VALUE_COLOR);
        x1 = (int) (xValueToScreen(value) - CIRCLE_WIDTH / 2.0);
        y1 = (int) (getHeight() - CIRCLE_WIDTH) / 2;
        g2.fillOval(x1, y1, CIRCLE_WIDTH, CIRCLE_WIDTH);
    }

    private double xValueToScreen(double xValue) {
        double gap = getWidth() * X_GAP;
        double scale = (double) (getWidth() - 2 * gap) / (2 * maxX);
        return (xValue + maxX) * scale + gap;
    }

    @Override
    public Dimension getPreferredSize() {
        if (isPreferredSizeSet()) {
            return super.getPreferredSize();
        }
        return new Dimension(PREF_W, PREF_H);
    }

    public double getValue() {
        return value;
    }

    public void setValue(double value) {
        this.value = value;
        repaint();
    }

    public int getMaxX() {
        return maxX;
    }

    public int getMajorTickCount() {
        return majorTickCount;
    }

    public int getMinorTicksPerMajor() {
        return minorTicksPerMajor;
    }
}

可以通过以下方式进行测试:

import java.awt.BorderLayout;
import javax.swing.BorderFactory;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JSlider;
import javax.swing.SwingUtilities;

@SuppressWarnings("serial")
public class NumberLine3Test extends JPanel {
    private static final int MAX_X = 40;
    private static final int MAJOR_TICS = 4;
    private static final int MINOR_TICS = 5;
    private double value = 0.0;
    private NumberLine3 numberLine3 = new NumberLine3(MAX_X, MAJOR_TICS, MINOR_TICS, value);
    private JSlider slider = new JSlider(-MAX_X, MAX_X, 0);

    public NumberLine3Test() {
        slider.setPaintTicks(true);
        slider.setMajorTickSpacing(10);
        slider.setMinorTickSpacing(5);
        slider.addChangeListener(ce -> {
            value = slider.getValue();
            numberLine3.setValue(value);
        });

        JPanel sliderPanel = new JPanel();
        sliderPanel.add(slider);
        int ebGap = 40;
        sliderPanel.setBorder(BorderFactory.createEmptyBorder(ebGap, ebGap, ebGap, ebGap));

        setLayout(new BorderLayout());
        add(numberLine3, BorderLayout.PAGE_START);
        add(sliderPanel);
    }

    private static void createAndShowGui() {
        NumberLine3Test mainPanel = new NumberLine3Test();

        JFrame frame = new JFrame("NumberLine3");
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.getContentPane().add(mainPanel);
        frame.pack();
        frame.setLocationRelativeTo(null);
        frame.setVisible(true);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(() -> createAndShowGui());
    }
}