使用滚动条动态显示面板的布局

Question

In java, I have been trying to create a panel that can accept other panels with a scroll bar.

I tried using gridlayout, and this works fine, except for the fact that if I only add a few panels, it grows those panels to fit the size of the parent panel.

I tried using flowlayout, but this makes the panels flow horizontally as there is a scroll bar.

How do I make it so I can add panels to the parent panel starting at the top and make them always the same size(or their preferred size).

Also, when I add panels to the parent panel after an event, they do not appear until after I move or resize the form. How do I make it repaint? calling repaint() on it did not work.

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();
            }
        });
    }
}

Answer 2

Assuming JScrollPane , see Sizing a Scroll Pane . For convenience, Scrollable clients such as JTable offer setPreferredScrollableViewportSize() , but you can always set the viewport's size explicitly.