在我的borderlayout中，我有JPanels，由数组theGrid引用。在一个单独的函数中，我想改变JPanel的外观，所以我改变了应该如何绘制特定的JPanel。我遇到的问题是，我不知道我现在如何绘制这个新版本的JPanel？
我已经查看了其他问题，并尝试在mainPanel或contentPane上使用.revalidate，.validate，.repaint（）等，或两者都没有，但是没有人会获得我创建的新版JPanel
在下面的构造函数中，我设置了网格以及它如何适应JFrame的其余部分
public class GraphicDisplay extends JFrame {
private static int ROWS = 6;
private static int COLS = 7;
private JPanel[][] theGrid = new JPanel[ROWS][COLS];
private JPanel mainPanel = new JPanel(new GridLayout(ROWS, COLS));
private Container contentPane;
public GraphicDisplay() {
for (int i = 0; i < theGrid.length; i++) { //Initialize theGrid (with blanks)
for (int j = 0; j < theGrid[i].length; j++) {
theGrid[i][j] = new JPanel();
}
}
//add them to the JFrame
contentPane = getContentPane();
contentPane.setLayout(new BorderLayout());
JPanel boardElements = new JPanel();
boardElements.setLayout(new BoxLayout(boardElements, BoxLayout.Y_AXIS)); //vertical layout for the two parts, theGrid itself and then the
// button which goes underneath,
final int SPACE = 3;
final Color COLORCHOICE = Color.BLACK;
mainPanel.setBorder(BorderFactory.createEmptyBorder(SPACE, SPACE, SPACE, SPACE));
mainPanel.setBackground(COLORCHOICE);
JPanel[][] panels = new JPanel[ROWS][COLS];
for (int i = 0; i < panels.length; i++) {
for (int j = 0; j < panels[i].length; j++) {
panels[i][j] = new JPanel(new GridLayout(1, 1, 1, 1));
panels[i][j].setBackground(COLORCHOICE);
panels[i][j].setBorder(BorderFactory.createEmptyBorder(SPACE, SPACE, SPACE, SPACE));
mainPanel.add(panels[i][j]);
panels[i][j].add(theGrid[i][j]);
}
}
//adding the grid to the vertical layout
boardElements.add(mainPanel);
//adding the button which will go directly under the grid
boardElements.add(new JButton("Button"));
contentPane.add(boardElements, BorderLayout.CENTER);
}
下面的函数属于同一类，假设通过在点3,3处添加一个点来更新网格（但问题是我没有看到任何明显的变化）
public void addDotToGrid() {
//theGrid[3][3] reference was added to the panels array which is part of the layout, so I would of thought by changing the value of it here would then change this JPanel on the UI
theGrid[3][3] = new JPanel() {
public void paintComponent( Graphics g) {
//g.setColor(Color.RED);
int y = 0;
int diameter = getWidth() -10;
int x = (getWidth()/2) - (diameter/2);
super.paintComponent(g);
Graphics2D g2d = (Graphics2D)g;
// Assume x, y, and diameter are instance variables.
Ellipse2D.Double circle = new Ellipse2D.Double(x, y, diameter, diameter);
g2d.fill(circle);
}
};
}
另一个创建GraphicDisplay对象的类的主方法
public static void main(String[] args) {
GraphicDisplay display2 = new GraphicDisplay();
display2.setSize(600, 600);
display2.setVisible(true);
display2.addDotToGrid();
}
问题是网格显示但是addDotToGrid（）没有改变任何东西，并且没有添加到网格的点
答案 0 :(得分：4)
您正在更改由theGrid数组保存的JPanel，但这对GUI中显示的JPanel没有任何影响，这会影响变量与引用或对象之间的关键区别 - 更改对象变量引用对它先前引用的对象没有影响。您的解决方案是更改网格所持有的JPanel。
这样做的一种方法是给所有绘制你想要的paintComponent方法，但让它们用布尔值控制，然后改变感兴趣的面板的布尔变量。
如果这是我的GUI，我会创建一个JLabel网格，只需在我想要的地方交换ImageIcons - 尽可能保持简单！
例如
import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.Font;
import java.awt.Graphics2D;
import java.awt.GridLayout;
import java.awt.RenderingHints;
import java.awt.event.ActionEvent;
import java.awt.event.MouseAdapter;
import java.awt.event.MouseEvent;
import java.awt.image.BufferedImage;
import javax.swing.*;
@SuppressWarnings("serial")
public class MyGridEg extends JPanel {
private static final int SPACE = 6;
private static final int ROWS = 6;
private static final int COLS = 7;
private static final int IMG_W = 80;
private static final int SML_GAP = 3;
private static final Color IMG_BACKG = new Color(240, 240, 240);
private static final String TITLE = "Click on a Cell";
private JLabel[][] labelGrid = new JLabel[ROWS][COLS];
private Icon blankIcon = createIconDisk(new Color(0, 0, 0, 0));
private Icon redIcon = createIconDisk(Color.RED);
public MyGridEg() {
MyMouse myMouse = new MyMouse();
JPanel gridHolder = new JPanel(new GridLayout(ROWS, COLS, SPACE, SPACE));
gridHolder.setBackground(Color.BLACK);
for (int i = 0; i < labelGrid.length; i++) {
for (int j = 0; j < labelGrid[i].length; j++) {
JLabel label = new JLabel(blankIcon);
label.addMouseListener(myMouse);
labelGrid[i][j] = label;
gridHolder.add(label);
}
}
gridHolder.setBorder(BorderFactory.createLineBorder(Color.black, SPACE));
JLabel titleLabel = new JLabel(TITLE, SwingConstants.CENTER);
titleLabel.setFont(titleLabel.getFont().deriveFont(Font.BOLD, 20));
JButton clearButton = new JButton(new ClearAction("Clear"));
JPanel btnPanel = new JPanel();
btnPanel.add(clearButton);
setLayout(new BorderLayout());
add(gridHolder, BorderLayout.CENTER);
add(btnPanel, BorderLayout.PAGE_END);
add(titleLabel, BorderLayout.PAGE_START);
}
private Icon createIconDisk(Color color) {
BufferedImage img = new BufferedImage(IMG_W, IMG_W, BufferedImage.TYPE_INT_ARGB);
Graphics2D g2 = img.createGraphics();
g2.setBackground(IMG_BACKG);
g2.clearRect(0, 0, IMG_W, IMG_W);
g2.setRenderingHint(RenderingHints.KEY_ANTIALIASING, RenderingHints.VALUE_ANTIALIAS_ON);
g2.setColor(color);
int x = SML_GAP;
int y = x;
int width = IMG_W - 2 * x;
int height = IMG_W - 2 * y;
g2.fillOval(x, y, width, height);
g2.dispose();
return new ImageIcon(img);
}
private class MyMouse extends MouseAdapter {
@Override
public void mousePressed(MouseEvent e) {
JLabel selected = (JLabel) e.getSource();
Icon icon = selected.getIcon() == blankIcon ? redIcon : blankIcon;
selected.setIcon(icon);
}
}
private class ClearAction extends AbstractAction {
public ClearAction(String name) {
super(name);
}
@Override
public void actionPerformed(ActionEvent e) {
for (JLabel[] labelRow : labelGrid) {
for (JLabel cell : labelRow) {
cell.setIcon(blankIcon);
}
}
}
}
private static void createAndShowGui() {
MyGridEg mainPanel = new MyGridEg();
JFrame frame = new JFrame("MyGridEg");
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());
}
}
这段代码的关键是我没有交换JLabel或JPanels，而是让我保持JLabel不变，但我正在改变它们的状态。这样，如果我改变2D数组labelGrid所持有的JLabel的状态，这可以通过视图中的更改来反映，就像我在clearButton JButton调用的ClearAction类中所做的那样：
private class ClearAction extends AbstractAction {
public ClearAction(String name) {
super(name);
}
@Override
public void actionPerformed(ActionEvent e) {
for (JLabel[] labelRow : labelGrid) {
for (JLabel cell : labelRow) {
cell.setIcon(blankIcon);
}
}
}
}