调试易

我用WMPLib获取多媒体文件播放时间时总是0？？这是为什么呢。
希望大家能帮帮忙。
 WMPLib.WindowsMediaPlayer wmp = new WindowsMediaPlayer();
        
        private void button2_Click(object sender, EventArgs e)
        {
            if (this.listBox1.SelectedItem != null)
            {
                this.textBox1.Text = this.listBox1.SelectedItem.ToString();
                this.Text = "[" + this.textBox1.Text.Substring(this.textBox1.Text.LastIndexOf("\\") + 1) + "]--精品音乐";
                wmp.URL = this.textBox1.Text;
                //22222
                
                //11111
                
                
                this.label2.Text = wmp.currentMedia.durationString;
                wmp.settings.setMode("loop", true);
                wmp.controls.play();
            }
            else
            {
                this.button1.PerformClick();
            }
        }