1.原理

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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() {
@Override
public void mouseClicked(MouseEvent e) {
isExpanded = !isExpanded;
panelVisible();
}

@Override
public void mouseEntered(MouseEvent e) {
label.setOpaque(true);
label.repaint();
}

@Override
public 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);
}
}

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