Java Swing编程之仿js树状折叠菜单

最近要完成一个需求：用swing做个树状菜单，含二级菜单，点击一级菜单展开二级菜单，且二级菜单数目超过预览视图会出现滚动条。由于swing研究的少，花了不少精力！

先看下测试效果图：

收起图：

展开图：

完整源码：

package com.xuwei.test2;

import java.awt.BorderLayout;
import java.awt.Color;
import java.awt.GridLayout;
import java.awt.event.ActionEvent;
import java.awt.event.ActionListener;

import javax.swing.JButton;
import javax.swing.JFrame;
import javax.swing.JPanel;
import javax.swing.JScrollPane;


public class TestFrm4 extends JFrame{
    private JButton btn1,btn2,btn3,btn4,btn5;
    private JPanel pNorth,pSouth,subMenuContainer;
    private JScrollPane pCenter;
    private JButton[] btn = null;
    private static boolean expand=false;
    
    public TestFrm4(){
        btn1=new JButton("Grade1 menu1");
        btn1.setBackground(Color.CYAN);
        btn2=new JButton("Grade1 menu2");
        btn2.setBackground(Color.CYAN);
        btn3=new JButton("Grade1 menu3");
        btn3.setBackground(Color.CYAN);
        btn3.addActionListener(new ActionHandler());
        
        btn4=new JButton("Grade1 menu4");
        btn4.setBackground(Color.CYAN);
        btn5=new JButton("Grade1 menu5");
        btn5.setBackground(Color.CYAN);
        pNorth=new JPanel();
        pNorth.setLayout(new GridLayout(3,1));
        pSouth=new JPanel();
        pSouth.setLayout(new GridLayout(2,1));
        subMenuContainer=new JPanel();
        subMenuContainer.setLayout(new GridLayout(25,1));
     
        btn=new JButton[25];        
        for(int i=0;i<btn.length;i++){
            btn[i]=new JButton("[菜单"+i+"]");
            btn[i].setBackground(Color.WHITE);
        }
        
        this.setLayout(new BorderLayout());
        
        pNorth.add(btn1); pNorth.add(btn2); pNorth.add(btn3); 
        for(int i=0;i<btn.length;i++){
            subMenuContainer.add(btn[i]);
        }
        pCenter=new JScrollPane(subMenuContainer);
        
        pSouth.add(btn4);pSouth.add(btn5);
        this.add(pNorth,"North");
        this.add(pCenter,"Center");
        this.add(pSouth,"South");
       
        this.setVisible(true);
        this.setSize(500,600);
        this.setResizable(false);
        this.setLocationRelativeTo(null);
        this.setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        
    }
    
    
    
    private class ActionHandler implements ActionListener{

        @Override
        public void actionPerformed(ActionEvent e) {
            if(btn3==e.getSource()){
                if(expand){//折叠
                   pNorth.setLayout(new GridLayout(3,1));
                   pNorth.remove(btn4);pNorth.remove(btn5);
                   pSouth.add(btn4);pSouth.add(btn5);
                   for(int i=0;i<btn.length;i++){
                       subMenuContainer.add(btn[i]);
                   }     
                   validate();
                   getContentPane().repaint();
                   expand=false;
                }else{//展开
                    for(int i=0;i<btn.length;i++){
                        subMenuContainer.remove(btn[i]);
                    }
                    pSouth.removeAll();
                    pNorth.setLayout(new GridLayout(5,1));
                    pNorth.add(btn4);
                    pNorth.add(btn5);
                    pNorth.repaint();
                    pCenter.repaint();
                    pSouth.repaint();
                    validate();
                    getContentPane().repaint();
                    expand=true;
                }
            }
        }
        
    }
    
    public static void main(String[] args) {
       
        new TestFrm4();
    }

}

这里频繁添加删除组件需要及时刷新界面，swing有几个方法要反复调用：

repaint(),validate(),invalidate(),doLayout().

之前我由于没调用validate()导致界面刷新出现很多问题！

swing要仔细研究发现东西也不少！