JFrame中的自定義圖形不顯示

Question

我正在設計一個帶狀圖，但未顯示。 正在顯示其封裝的JFrame，並且正在調用paintComponent() ，但是沒有出現灰色網格線。 為什么是這樣？

class ChartArea extends JPanel {

        private int Yscl, Xscl;
        private static final Color BACKGROUND_COLOR = Color.BLACK;
        private static final Color LINE_COLOR = Color.GREEN;
        private static final Color GRIDLINE_COLOR = Color.GRAY;

        ChartArea() {
            setBackground(BACKGROUND_COLOR);
            setForeground(LINE_COLOR);
            Yscl = 20;
            Xscl = 20;
        }

        @Override
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            Graphics2D g2d = (Graphics2D) g;
            int height = getHeight();
            int width = getWidth();
            double max = data.getMax(); //gets the maximum value in the data set

            try {
                g2d.setStroke(new BasicStroke(1f, BasicStroke.CAP_BUTT, BasicStroke.JOIN_MITER));

                //put the origin in the bottom right. Positive is up and left
                g2d.translate(width, height);
                g2d.scale(-1d, -1d);

                //if the data set exceeds the window height, scale it down
                if (max > height) {
                    g2d.scale(1, height / max);
                }
                paintGrid(g2d);
                paintLine(g2d);
            } finally {
                g2d.dispose();
            }
        }

        private void paintGrid(Graphics2D g) {
            g.setPaint(GRIDLINE_COLOR);

            //Vertical Lines
            for (double pos = 0; pos > getWidth(); pos += Xscl) {
                Line2D line = new Line2D.Double(pos, 0d, pos, getHeight());
                g.draw(line);
            }

            //Horizontal Lines
            for (double pos = 0; pos > getHeight(); pos += Yscl) {
                Line2D line = new Line2D.Double(0d, pos, getWidth(), pos);
                g.draw(line);
            }
        }

        private void paintLine(Graphics2D g) {
            g.setPaint(LINE_COLOR);
            Path2D plot2 = new Path2D.Double();

            if (!data.isEmpty()) {
                plot2.moveTo(0.0, data.get(0));
                for (int i = 1; i < data.size(); i++) {
                    plot2.lineTo((double) i, data.get(i));
                }
                g.draw(plot2);
            }
        }

Answer 1

看起來在for循環條件中有錯別字會畫線。 循環永遠不會在當前條件下執行。 如果將條件更改為pos < getWidth(); 和pos < getHeight(); 您應該看到網格。 這是一個完整的方法：

private void paintGrid(Graphics2D g) {
    g.setPaint(GRIDLINE_COLOR);

    //Vertical Lines
    //for (double pos = 0; pos > getWidth(); pos += Xscl) {
    for (double pos = 0; pos < getWidth(); pos += Xscl) {
        Line2D line = new Line2D.Double(pos, 0d, pos, getHeight());
        g.draw(line);
    }

    //Horizontal Lines
    //for (double pos = 0; pos > getHeight(); pos += Yscl) {
    for (double pos = 0; pos < getHeight(); pos += Yscl) {
        Line2D line = new Line2D.Double(0d, pos, getWidth(), pos);
        g.draw(line);
    }
}

結果如下：

Answer 2

您要覆蓋paintComponent以便僅繪制您的自定義面板。 您只需要繪制父實例。

@Override
public void paintComponent(Graphics g) {
    super.paintComponent(g);
    // custom painting
}