java - 多个 JPanel 未打印在背景前面

Question

我想创建一个日历，根据它所基于的月份动态地创建自己。首先，我创建了一个将在任何月份使用的背景，其尺寸为 700x500(每天为 700/7，每月为 500/5，但 28 天-二月开始-周一有 5 行)周)。我用这句话做到了这一点:

public class Graph {

    private final int sizeX = 700;
    private final int sizeY = 500;
    private Calendar calendar;


    public Graph(Calendar calendar) {
        this.calendar = calendar;
        JFrame frame = new JFrame();
        graph(frame);
    }

    public void graph(JFrame frame) {
        buildBackground(frame);
    }

    private void buildBackground(JFrame frame) {
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        frame.setVisible(true);
        frame.setSize(sizeX, sizeY);
        JPanel panel = new Background(sizeX, sizeY);
        frame.add(panel);
        frame.validate();
        frame.repaint();
    }
}

public class Background extends JPanel {

    private int sizeX;
    private int sizeY;

    public Background(int sizeX, int sizeY) {
        this.sizeX = sizeX;
        this.sizeY = sizeY;
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(Color.DARK_GRAY);
        g.fillRect(0, 0, sizeX, sizeY);
    }
}

并且工作正常，深灰色背景已正确创建。当我尝试创建代表日期的小矩形时，问题就出现了；我设计了一个类，我想在某个坐标上表示这些矩形:

public class DayRectangle extends JPanel {

    private int posX;
    private int posY;
    private int day;

    public DayRectangle(int posX, int posY, int day) {
        this.posX = posX;
        this.posY = posY;
        this.day = day;
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.fillRect(posX, posY, 60, 60);
    }

    public Dimension getPreferredSize() {
        return new Dimension (60, 60);
    }

    @Override
    public String toString() {
        return String.format("(%d,%d):%d", posX, posY, day);
    }
}

矩形的坐标已正确创建，因为这是 DayRectangle 的 ArrayList 的内容:

[(20,20):1, (120,20):2, (220,20):3, (320,20):4, (420,20):5, (520,20):6, (620,20):7, (20,120):8, (120,120):9, (220,120):10, (320,120):11, (420,120):12, (520,120):13, (620,120):14, (20,220):15, (120,220):16, (220,220):17, (320,220):18, (420,220):19, (520,220):20, (620,220):21, (20,320):22, (120,320):23, (220,320):24, (320,320):25, (420,320):26, (520,320):27, (620,320):28, (20,420):29, (120,420):30, (220,420):31]

它们从 (20, 20) 开始，因为我想在这些矩形之间留一些间隙。

主要问题是当我执行此代码时没有打印矩形:

public void graph(JFrame frame) {
    buildBackground(frame);
    frame.getGraphics().setColor(Color.WHITE);
    JPanel panel;
    for (DayRectangle d : arraylist) {
        panel = d;
        frame.add(panel);
        frame.repaint();
    }
}

我做错了什么？为什么没有打印任何内容？谢谢。

Answer 1

您似乎忘记了 JFrame 使用 BorderLayout 作为其布局管理器。相反，您应该将 Day JPanel 添加到另一个使用 GridLayout 的 JPanel 中，并且还要记住 Day JPanel 将相对于它们自己的本地坐标系进行绘制，因此每个 Day JPanel 可能应该在同一位置绘制其矩形，从 0 附近开始, 0，不相对于包含容器。

如果您希望一个 JPanel 成为背景 JPanel，则应将其添加到 JFrame 的 BorderLayout.CENTER 位置。给它一个 GridLayout，并向其中添加您的 Day JPanel 以及任何所需的 JLabels(如果您需要空方 block ，则为空)。另外，如果您希望显示背景图像或颜色，则 Day 可能需要不透明。

例如，

public class DayRectangle extends JPanel {
    private static Color RECT_COLOR = Color.LIGHT_GRAY;
    private static final int PREF_W = 60;
    private static final int GAP = 4;
    private int posX;
    private int posY;
    private int day;

    public DayRectangle(int posX, int posY, int day) {
        this.posX = posX; // not sure that you need this
        this.posY = posY; // ditto
        this.day = day;

        // if you desire a background to show throw
        // setOpaque(false);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(RECT_COLOR);
        g.fillRect(GAP, GAP, PREF_W - 2 * GAP, PREF_W - 2 * GAP);
    }

    public Dimension getPreferredSize() {
        return new Dimension(PREF_W, PREF_W);
    }

    @Override
    public String toString() {
        return String.format("(%d,%d):%d", posX, posY, day);
    }
}

举个简单的例子:

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Dimension;
import java.awt.Font;
import java.awt.Graphics;
import java.awt.GridBagLayout;
import java.awt.GridLayout;
import javax.swing.*;

@SuppressWarnings("serial")
public class ExampleGrid extends JPanel {
    public ExampleGrid() {

        JPanel mainGrid = new JPanel();
        mainGrid.setLayout(new GridLayout(0, 7));
        // just to show a little off-set of the days
        mainGrid.add(new JLabel());
        mainGrid.add(new JLabel());
        mainGrid.add(new JLabel());

        // now fill the calendar
        for (int i = 0; i < 30; i++) {
            mainGrid.add(new DayRectangle(i + 1));
        }

        JLabel monthLabel = new JLabel("JULY", SwingConstants.CENTER);
        monthLabel.setFont(monthLabel.getFont().deriveFont(Font.BOLD, 36f));

        // label the days of the week at the top
        String[] daysOfWk = { "Sun", "Mon", "Tues", "Wed", "Thur", "Fri", "Sat" };
        JPanel daysOfWkPanel = new JPanel(new GridLayout(1, 7));
        for (String dayOfWk : daysOfWk) {
            daysOfWkPanel.add(new JLabel(dayOfWk, SwingConstants.CENTER));
        }

        JPanel topPanel = new JPanel(new BorderLayout());
        topPanel.add(monthLabel, BorderLayout.PAGE_START);
        topPanel.add(daysOfWkPanel, BorderLayout.CENTER);

        setLayout(new BorderLayout());
        add(topPanel, BorderLayout.PAGE_START);
        add(mainGrid, BorderLayout.CENTER);
    }

    @Override
    protected void paintComponent(Graphics g) {
        super.paintComponent(g);
        // not sure what you want to do here
    }

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

        JFrame frame = new JFrame("Example Grid");
        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());
    }
}

@SuppressWarnings("serial")
class DayRectangle extends JPanel {
    private static Color RECT_COLOR = Color.LIGHT_GRAY;
    private static final int PREF_W = 60;
    private static final int GAP = 4;
    private static final float FNT_SZ = 20f;
    private int day;

    public DayRectangle(int day) {
        this.day = day;

        setLayout(new GridBagLayout());

        JLabel label = new JLabel("" + day);
        label.setFont(label.getFont().deriveFont(Font.BOLD, FNT_SZ));
        add(label);

        // if you desire a background to show throw
        // setOpaque(false);
    }

    @Override
    public void paintComponent(Graphics g) {
        super.paintComponent(g);
        g.setColor(RECT_COLOR);
        g.fillRect(GAP, GAP, PREF_W - 2 * GAP, PREF_W - 2 * GAP);
    }

    public Dimension getPreferredSize() {
        return new Dimension(PREF_W, PREF_W);
    }

    public int getDay() {
        return day;
    }

}