JSwing - 从构造函数中调用子例程不会初始化数组（它应该这样做）

Question

我有一个 PieChart class，它扩展了我用来绘制（你相信吗）饼图的 JPanel 组件。

我有一个名为 createArcs() 的子例程，它创建用于绘制饼图的圆弧数组。必须在 class 中的其他地方访问正在创建的这些弧线（用于测试鼠标是否在它们上方）。

当我从 paintComponent() 子例程中调用 createArcs() 时，一切正常。这并不完全理想，因为这意味着每次调用 paintComponent() 时都会不必要地重新计算弧线。

当从构造函数中调用 createArcs() 时，JPanel 会弹出，但只会绘制背景。我还有其他正在测试的图形对象，它们也无法渲染除背景（纯白色）以外的任何内容。它也看起来好像数组已经被初始化，因为我可以从 paintComponent() 子内部访问数组中弧的属性，它只是无法绘制它们。

下面是工作代码，我想从构造函数而不是 paintComponent() 子函数中调用 createArcs()。感谢您提供的所有帮助 :).

对于任何格式错误，我深表歉意，我是新手 :^)

import java.awt.*;
import java.awt.geom.Arc2D;

import javax.swing.*;

public class PieChart extends JPanel {

public static final int xBuffer = 10;
public static final int yBuffer = 10;

public Arc2D arcs[];

private static final long serialVersionUID = 1L;

int y[];

public PieChart(int y[]) { //Constructor sets up the array
    this.y = y;
}

public void setBounds(int x, int y, int width) { //Overrides so that the panel can only ever be a square
    super.setBounds(x, y, width, width);
}

public int getSegment(int x, int y) {
    int ret = -1;
    for (int i = 0; i < arcs.length; i++) {
        if (arcs[i].contains(x, y)) {
            ret = i;
        }
    }
    return ret;
}

public void paintComponent(Graphics g) {

    //Arcs are calculated every time paintComponent is called :((
    createArcs();
    //Sets up background
    super.paintComponent(g);
    g.setColor(Color.WHITE);
    g.fillRect(0, 0, getWidth(), getHeight());

    //Create an array same size as the int array

    Graphics2D g2 = (Graphics2D) g;

    g.setColor(Util.generateColor(true));

    //Draws the arcs for the pie chart
    g.setColor(Util.generateColor(true));
    for (int i = 0; i < arcs.length; i++) {
        g2.fill(arcs[i]);
        g.setColor(Util.generateColor(false));
    }

}

public void createArcs() {
    arcs = new Arc2D[y.length];
    float normalisedY[] = new float[y.length];

    int maxY = 0;
    int total = 0;

    //Find maximum element and total of the data
    for (int i = 0; i < y.length; i++) {
        if (maxY < y[i]) {
            maxY = y[i];
        }
        total += y[i];
    }

    //Normalise the Y values in degrees
    for (int i = 0; i < y.length; i++) {
        normalisedY[i] = 360 * (((float) y[i] / (float) total));
    }

    int degreesTravelled = 0;
    //Creates arcs in a circle
    for (int i = 0; i < normalisedY.length; i++) {
        Arc2D arc = new Arc2D.Double(0, 0, getWidth(), getHeight(), degreesTravelled, Math.round(normalisedY[i]), Arc2D.PIE);
        arcs[i] = arc;
        degreesTravelled += Math.round(normalisedY[i]);
    }
}

}

这是无法运行的代码：

import java.awt.*;
import java.awt.geom.Arc2D;

import javax.swing.*;

public class PieChart extends JPanel {

public static final int xBuffer = 10;
public static final int yBuffer = 10;

public Arc2D arcs[];

private static final long serialVersionUID = 1L;

int y[];

public PieChart(int y[]) { //Constructor sets up the array
    this.y = y;
    createArcs();
}

public void setBounds(int x, int y, int width) { //Overrides so that the panel can only ever be a square
    super.setBounds(x, y, width, width);
}

public int getSegment(int x, int y) {
    int ret = -1;
    for (int i = 0; i < arcs.length; i++) {
        if (arcs[i].contains(x, y)) {
            ret = i;
        }
    }
    return ret;
}

public void paintComponent(Graphics g) {

    //Arcs are calculated every time paintComponent is called :((

    //Sets up background
    super.paintComponent(g);
    g.setColor(Color.WHITE);
    g.fillRect(0, 0, getWidth(), getHeight());

    //Create an array same size as the int array

    Graphics2D g2 = (Graphics2D) g;

    g.setColor(Util.generateColor(true));

    //Draws the arcs for the pie chart
    g.setColor(Util.generateColor(true));
    for (int i = 0; i < arcs.length; i++) {
        g2.fill(arcs[i]);
        g.setColor(Util.generateColor(false));
    }

}

public void createArcs() {
    arcs = new Arc2D[y.length];
    float normalisedY[] = new float[y.length];

    int maxY = 0;
    int total = 0;

    //Find maximum element and total of the data
    for (int i = 0; i < y.length; i++) {
        if (maxY < y[i]) {
            maxY = y[i];
        }
        total += y[i];
    }

    //Normalise the Y values in degrees
    for (int i = 0; i < y.length; i++) {
        normalisedY[i] = 360 * (((float) y[i] / (float) total));
    }

    int degreesTravelled = 0;
    //Creates arcs in a circle
    for (int i = 0; i < normalisedY.length; i++) {
        Arc2D arc = new Arc2D.Double(0, 0, getWidth(), getHeight(), degreesTravelled, Math.round(normalisedY[i]), Arc2D.PIE);
        arcs[i] = arc;
        degreesTravelled += Math.round(normalisedY[i]);
    }
}

}

Answer 1

Arc2D arc = new Arc2D.Double(0, 0, getWidth(), getHeight(), degreesTravelled, Math.round(normalisedY[i]), Arc2D.PIE);

看起来你有基于面板 width/height 的逻辑。

显然，在创建面板时，在框架可见之前不会有大小。

绘制方法应该只绘制组件的状态，而不是改变状态。

因此，您可能需要向面板添加一个 ComponentListener 以侦听面板大小的变化，此时您将初始化数组中的值。

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