1.原理
原理非常简单：就是一个JLabel和JPanel。Jlabel显示标题文字以及标明控件当前是处于展开还是折叠状态的图片；而JPanel主要就一个作用――承载控件的容器。JLabel通过响应鼠标事件来控制JPanel是否显示。这样就可以达到折叠或展开的效果。
下面话不多说了，来一起看看详细的示例代码
2.代码
public class JShrinkablePanel extends JPanel {private JLabellabel;private Stringtitle ="";private JPanelcontentPanel =null;private boolean isExpanded =true;private JListlist =new JList();private IconiconExpand =null;private IconiconCollapse =null;public JShrinkablePanel(String title, JPanel contentPanel) {super();this.title = title;this.contentPanel = contentPanel;initComponents();initComponentsStatus();initLayout();initResources();unRegisterEvents();registerEvents();}private void initComponents() {this.label =new JLabel();}private void initComponentsStatus() {this.label.setHorizontalAlignment(JLabel.LEFT);this.label.setVerticalAlignment(JLabel.CENTER);this.label.setVerticalTextPosition(JLabel.CENTER);this.label.setBackground(this.list.getSelectionBackground());this.iconExpand =new ImageIcon("src/Resources/Expand.png");this.iconCollapse =new ImageIcon("src/Resources/Collapse.png");}private void initLayout() {this.setLayout(new GridBagLayout());this.add(this.label,new GridBagConstraints(0,0,1,1,1,0, GridBagConstraints.WEST, GridBagConstraints.HORIZONTAL,new Insets(0,0,0,0),0,0));this.add(this.contentPanel,new GridBagConstraints(0,1,1,1,1,0, GridBagConstraints.WEST, GridBagConstraints.HORIZONTAL,new Insets(0,0,0,0),0,0));}private void initResources() {this.label.setIcon(this.iconExpand);this.label.setText(this.title);}private void unRegisterEvents() {this.label.removeMouseListener(this.mouseListener);}private void registerEvents() {this.label.addMouseListener(this.mouseListener);}private MouseListenermouseListener =new MouseAdapter() {@Overridepublic void mouseClicked(MouseEvent e) {isExpanded = !isExpanded;panelVisible();}@Overridepublic void mouseEntered(MouseEvent e) {label.setOpaque(true);label.repaint();}@Overridepublic void mouseExited(MouseEvent e) {label.setOpaque(false);label.repaint();}};private void panelVisible() {this.contentPanel.setVisible(this.isExpanded);this.label.setIcon(this.isExpanded ?this.iconExpand :this.iconCollapse);}public static void main(String[] args) {JFrame jf =new JFrame("JShrinkablePanel");jf.setBounds(400,200,400,300);jf.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);JPanel panel=new JPanel();panel.add(new JButton("Just for show"));panel.setBorder(BorderFactory.createTitledBorder("Border"));JShrinkablePanel scrollPane=new JShrinkablePanel("TestJShrinkablePanel",panel);jf.add(scrollPane);jf.setVisible(true);}}3.效果
panel展开鼠标在标题Label上
panel展开鼠标没在标题Label上
panel折叠鼠标在标题Label上
panel折叠鼠标没在标题Label上
总结
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