java - 使用滚动条动态显示面板的布局

Question

在 java 中，我一直在尝试创建一个可以接受其他带有滚动条的面板的面板。

我尝试使用 gridlayout，效果很好，除了如果我只添加几个面板，它会增加这些面板以适应父面板的大小。

我尝试使用 flowlayout，但这会使面板水平流动，因为存在滚动条。

我该怎么做才能将面板添加到从顶部开始的父面板，并使它们始终具有相同的大小(或它们的首选大小)。

另外，当我在事件后将面板添加到父面板时，它们直到我移动或调整表单大小后才会出现。我如何让它重绘？对其调用 repaint() 无效。

Answer 1

import java.awt.*;
import java.awt.event.*;
import javax.swing.*;
import javax.swing.border.*;

/** This lays out components in a column that is constrained to the
top of an area, like the entries in a list or table.  It uses a GridLayout
for the main components, thus ensuring they are each of the same size.
For variable height components, a BoxLayout would be better. */
class ConstrainedGrid {

    ConstrainedGrid() {
        final JPanel gui = new JPanel(new BorderLayout(5,5));
        gui.setBorder(new EmptyBorder(3,3,3,3));
        gui.setBackground(Color.red);

        JPanel scrollPanel = new JPanel(new BorderLayout(2,2));
        scrollPanel.setBackground(Color.green);
        scrollPanel.add(new JLabel("Center"), BorderLayout.CENTER);
        gui.add(new JScrollPane(scrollPanel), BorderLayout.CENTER);

        final JPanel componentPanel = new JPanel(new GridLayout(0,1,3,3));
        componentPanel.setBackground(Color.orange);
        scrollPanel.add(componentPanel, BorderLayout.NORTH);

        JButton add = new JButton("Add");
        gui.add(add, BorderLayout.NORTH);
        add.addActionListener( new ActionListener() {
            public void actionPerformed(ActionEvent ae) {
                componentPanel.add(new JTextField());
                gui.validate();
            }
        });

        Dimension d = gui.getPreferredSize();
        d = new Dimension(d.width, d.height+100);
        gui.setPreferredSize(d);

        JOptionPane.showMessageDialog(null, gui);
    }

    public static void main(String[] args) {
        SwingUtilities.invokeLater(new Runnable() {
            public void run() {
                ConstrainedGrid cg = new ConstrainedGrid();
            }
        });
    }
}