我加的滚动条为什么不显示呢？

Question

谢谢版主,我增加了pnlLeft.setPreferredSize(new Dimension(300, 200));pnlRight.setPreferredSize(new Dimension(300, 200));这样两个panel是大小控制住了，但是滚动条还是没显示出来。

Answer 1

你给JScrollPane 加上这两个方法看看
setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS);

Answer 2

调整了一下解决了
/**
 * 主面板
 */
public void mainPanel() {
Container contentPane = this.getContentPane();
JPanel title = new JPanel();
JLabel lblTitle = new JLabel("图片压缩前后效果比对", JLabel.CENTER);
title.setBackground(Color.WHITE);
title.add(lblTitle);
contentPane.add(title, BorderLayout.NORTH);
// 主面板
JPanel main = new JPanel();
main.setBackground(Color.WHITE);
main.setLayout(new BoxLayout(main, BoxLayout.X_AXIS));
main.setVisible(true);
contentPane.add(main);

// 左边面板
JPanel pnlLeft = new JPanel();
// 左边原始图片
JLabel lblSource = new JLabel();
lblSource.setIcon(getIcon("F:\\MyDocument\\RainBoy\\Desktop\\11.jpg"));
// 左边滚动条
final JScrollPane scrollLeftPane = new JScrollPane(lblSource);
pnlLeft.add(scrollLeftPane);
scrollLeftPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
scrollLeftPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS); 
scrollLeftPane.setPreferredSize(new Dimension(WIDTH/2, HEIGHT/2));
main.add(scrollLeftPane);
// 右侧面板
JPanel pnlRight = new JPanel();

// 右边处理图片
JLabel lblTaget = new JLabel();
lblTaget.setIcon(getIcon("F:\\MyDocument\\RainBoy\\Desktop\\Thumb122.jpg"));
// 右边滚动条
final JScrollPane scrollRightPane = new JScrollPane(lblTaget);
pnlRight.add(scrollRightPane);
scrollRightPane.setVerticalScrollBarPolicy(ScrollPaneConstants.VERTICAL_SCROLLBAR_ALWAYS);
scrollRightPane.setHorizontalScrollBarPolicy(ScrollPaneConstants.HORIZONTAL_SCROLLBAR_ALWAYS); 
scrollRightPane.setPreferredSize(new Dimension(WIDTH/2, HEIGHT/2));
main.add(scrollRightPane);
scrollLeftPane.addAncestorListener(new AncestorListener(){
public void ancestorMoved(AncestorEvent event) {
JScrollBar jScrollBarLeft = scrollLeftPane.getHorizontalScrollBar();
int i = jScrollBarLeft.getValue();
JScrollBar jScrollBarRight = scrollRightPane.getHorizontalScrollBar();
jScrollBarRight.setValue(jScrollBarLeft.getValue());
} public void ancestorAdded(AncestorEvent event) {
} public void ancestorRemoved(AncestorEvent event) {
}
}); }但现在有个问题。两边的滚动条无法同步滚动。即我拖动左边的滚动条，想让右边的也进行滚动