C# 遍历文件夹下所有子文件夹中的文件，得到文件名

假设a文件夹在F盘下，代码如下。将文件名输出到一个ListBox中
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace WindowsFormsApplication1
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        private void button2_Click(object sender, EventArgs e)
        {
            DirectoryInfo theFolder = new DirectoryInfo(@"F:a");
            DirectoryInfo[] dirInfo = theFolder.GetDirectories();
            //遍历文件夹
            foreach (DirectoryInfo NextFolder in dirInfo)
            { 
               // this.listBox1.Items.Add(NextFolder.Name);
                FileInfo[] fileInfo = NextFolder.GetFiles();        
                foreach (FileInfo NextFile in fileInfo)  //遍历文件
                this.listBox2.Items.Add(NextFile.Name); 
            }

        }
    }
}