c#播放器

using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.IO;

namespace boxs
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }
        List<string> a = new List<string>();
        private void button1_Click(object sender, EventArgs e)
        {
            OpenFileDialog od = new OpenFileDialog();
            od.Title = "xx";
            od.InitialDirectory = @"C:\Documents and Settings\Administrator\桌面";
            od.Filter = "";
            od.Multiselect = true;
            od.ShowDialog();
            string[] names = od.FileNames;
            foreach (string path in names)
            {
                string s_name = Path.GetFileName(path);
                listBox1.Items.Add(s_name);
                a.Add(path);
            }

        }

        private void listBox1_DoubleClick(object sender, EventArgs e)
        {
            string ax = Convert.ToString(a[listBox1.SelectedIndex]);
            axWindowsMediaPlayer1.URL = ax;
            this.button2.Text = "暂停";

        }
        private bool b = false;
        private void button2_Click(object sender, EventArgs e)
        {
            if (this.button2.Text == "播放")
            {
                if (listBox1.Items.Count < 1 || listBox1.SelectedIndex<0)
                {
                    MessageBox.Show("代码错了");
                    return;
                }
                    if (b){

                        b = false;

                    }
                    else {
                        string ax = Convert.ToString(a[this.listBox1.SelectedIndex]);
                        axWindowsMediaPlayer1.URL = ax;

                    }
                    axWindowsMediaPlayer1.Ctlcontrols.play();
                    this.button2.Text = "暂停";

            }
            else {
                axWindowsMediaPlayer1.Ctlcontrols.pause();
                this.button2.Text = "播放";
                b = true;

            }
        }

        private void listBox1_SelectedIndexChanged(object sender, EventArgs e)
        {
            b = false;
        }
    }
}