java - GridLayout 单元格真的都是相同大小吗？

Question

我决定为我的 Java Swing 应用程序使用 GridLayout LayoutManager 因为网格中的每个单元格应该具有完全相同的大小。

来自the Java Tutorials :

A GridLayout object places components in a grid of cells. Each component takes all the available space within its cell, and each cell is exactly the same size.

甚至在 GridLayout 的描述中类:

The GridLayout class is a layout manager that lays out a container's components in a rectangular grid. The container is divided into equal-sized rectangles, and one component is placed in each rectangle.

但是，我的代码似乎使某个单元格大小是其他单元格的两倍。我使用 GridLayout 将 3 个 JPanel 添加到 Container 中，并为每个 JPanel 提供了不同的背景颜色。结果是这样的:

显然，第一个 JPanel(红色背景)是其他 JPanel(绿色和黄色)的两倍大。生成此代码的代码如下:

public void updateListFrameContentPane(Container mainPane) {
    mainPane.setLayout(new GridLayout(1,0));
    JPanel listPanel = new JPanel();
    listPanel.setLayout(new BoxLayout(listPanel, BoxLayout.Y_AXIS));
    listPanel.add(friendsLabel);        
    listPanel.add(listScrollPane);
    listPanel.setBackground(Color.RED);
    mainPane.add(listPanel);
    for(JPanel chatPanel : chatPanels) {
        chatPanel.setBackground((Math.random()>0.5 ? Color.YELLOW : Color.GREEN));
        mainPane.add(chatPanel);
    }
}

我所做的就是将 Container's 布局设置为具有 1 行和任意数量列的 GridLayout，然后向其中添加 3 个 JPanels。那么为什么第一个 JPanel 这么大呢？奇怪的是，只有当添加两个或更多 chatPanel 时才会发生这种情况。当只有一个时，它的格式正确。

Answer 1

基赫鲁是对的。更改容器内容后重新验证/重新绘制。这是一个粗略但有效的示例:

public class GridLayoutExample {

private JFrame frame;
private Map<String,JPanel> chatBoxes = new HashMap<String,JPanel>();
private String lastKey = "0";

public static void main(String[] args) {
    EventQueue.invokeLater(new Runnable() {
        public void run() {
            try {
                GridLayoutExample window = new GridLayoutExample();
                window.frame.setVisible(true);
            } catch (Exception e) {
                e.printStackTrace();
            }
        }
    });
}

/**
 * Create the application.
 */
public GridLayoutExample() {
    initialize();
}

private void addChatBox() {
    /*
     * JPanel (border layout)
     * - JPanel (Border South, Border layout)
     * - - JTextField ( Border center )
     * - - JButton ( Border east )
     * - JLabel (Border North )
     * - JTextArea (Border Center);
     */
    int lk = Integer.valueOf(lastKey)+1;
    lastKey = Integer.toString(lk);
    JPanel np = new JPanel();
    np.setLayout(new BorderLayout(0,0));
    np.setBackground((lk%2 == 0) ? Color.GREEN : Color.YELLOW);

    JPanel south = new JPanel();
    south.setLayout(new BorderLayout(0,0));
    np.add(south,BorderLayout.SOUTH);

    JButton b = new JButton("New Button");
    south.add(b,BorderLayout.EAST);

    JTextField field = new JTextField();
    south.add(field,BorderLayout.CENTER);

    JLabel label = new JLabel(lastKey);
    label.setHorizontalAlignment(SwingConstants.CENTER);
    np.add(label,BorderLayout.NORTH);

    JTextArea text = new JTextArea();
    np.add(text,BorderLayout.CENTER);

    chatBoxes.put(lastKey, np);
    frame.getContentPane().add(np);
    frame.revalidate();                 // CRITICAL MISSING LINES
    frame.repaint();                    // CRITICAL MISSING LINES
}

/**
 * Initialize the contents of the frame.
 */
private void initialize() {
    frame = new JFrame();
    frame.setBounds(100, 100, 923, 300);
    frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
    frame.getContentPane().setLayout(new GridLayout(1, 0, 0, 0));

    JPanel panel = new JPanel();
    panel.setBackground(Color.RED);
    frame.getContentPane().add(panel);
    panel.setLayout(new BoxLayout(panel, BoxLayout.Y_AXIS));

    JLabel lblNewLabel = new JLabel("Online Users");
    panel.add(lblNewLabel);

    JList list = new JList();
    list.addMouseListener(new MouseAdapter() {
        @Override
        public void mouseClicked(MouseEvent e) {
            addChatBox();
        }
    });
    list.setModel(new AbstractListModel() {
        String[] values = new String[] {"Alpha", "Beta", "Gamma", "Delta", "Epsilon"};
        public int getSize() {
            return values.length;
        }
        public Object getElementAt(int index) {
            return values[index];
        }
    });
    panel.add(list);

}
}

我选择重新验证/重新绘制整个框架，但在重新绘制较小的容器时可能会使其工作。当然，如果没有上面标记的关键行，无论您单击列表元素的频率如何，都不会显示任何新内容。通过这些行，每次单击时都会添加一个新的聊天框。

嗯...刚刚注意到这一点。如果红色区域被认为是两个单独的面板，那么它们的尺寸都是完全正确的。您是否可能不小心添加了额外的面板？