如何检测JScrollPane的滚动条是否会更改可见性？

Question

我有JScrollPane包含水平行中的一些图像.如果视图端口的图像行太长,则JScrollPane会显示滚动条,从而降低视图端口的高度.我想调整图像大小以适应视口.如何检测视口改变其大小？不幸的是,注册更改事件处理程序似乎不起作用.

Answer 1

在ViewPort上使用更改侦听器似乎对我有用.这是一个小的演示:

import java.awt.BorderLayout;
import java.io.UnsupportedEncodingException;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;
import javax.swing.SwingWorker;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;

public class Main {

    public static void main(String[] args) throws UnsupportedEncodingException {
        JFrame frame = new JFrame();
        frame.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        JPanel panel = new JPanel(new BorderLayout());
        final JPanel buttons = new JPanel();
        final JScrollPane pane = new JScrollPane(buttons);
        pane.getViewport().addChangeListener(new ChangeListener() {

            @Override
            public void stateChanged(ChangeEvent e) {
                System.err.println("Change in " + e.getSource());
                System.err.println("Vertical visible? " + pane.getVerticalScrollBar().isVisible());
                System.err.println("Horizontal visible? " + pane.getHorizontalScrollBar().isVisible());
            }
        });
        panel.add(pane);
        frame.setContentPane(panel);
        frame.setSize(300, 200);
        frame.setVisible(true);
        SwingWorker<Void, Void> worker = new SwingWorker<Void, Void>() {

            @Override
            protected Void doInBackground() throws Exception {
                for (int i = 0; i < 10; i++) {
                    Thread.sleep(800);
                    buttons.add(new JButton("Hello " + i));
                    buttons.revalidate();
                }
                return null;
            }
        };
        worker.execute();
    }
}