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带滚动条的其他面板的面板.

我尝试使用gridlayout,这很好用,除了我只添加几个面板的事实,它增长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,因为有一个滚动条.

我如何制作它以便我可以从顶部开始向父面板添加面板并使它们始终具有相同的尺寸(或它们的首选尺寸).

此外,当我在事件后向父面板添加面板时,直到我移动或调整窗体大小后才会显示它们.我怎么做它重绘？在它上面调用repaint()不起作用.

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();
            }
        });
    }
}