C#中OpenFileDialog的设置问题

static void Main()
{
OpenFileDialog d = new OpenFileDialog();
d.Filter = "可播放文件(*.mp3,*.wma,*.rm)|*.Mp3;*.wma;*.rm";
d.FileOk += new System.ComponentModel.CancelEventHandler(d_FileOk);

}

static void d_FileOk(object sender, System.ComponentModel.CancelEventArgs e)
{
OpenFileDialog d = sender as OpenFileDialog;
if (d.FileName.EndsWith(".txt"))
{
MessageBox.Show("楼主说不能选择txt文件！选择txt文件木有小JJ");
// 你想加上其他限制，就在这里判断，我随便写一句，不是重点。
e.Cancel = true;
}
}

private void openFileDialog1_FileOk(object sender, CancelEventArgs e)
{
string ext = Path.GetExtension(openFileDialog1.FileName);
if(string.Compare(ext,".txt")==0)
MessageBox.Show("楼主说不能选择txt文件！选择txt文件木有小JJ");
}

private void button1_Click(object sender, EventArgs e)
{
openFileDialog1.FileOk += openFileDialog1_FileOk;
openFileDialog1.Filter = "可播放文件|*.mp3;*.wma;*.rm";
openFileDialog1.ShowDialog();
}