菜鸟问题？求教~我用了某位老师的程序改动~其中lstFiles 表中 获取不到String值

private void OpenThreeFile()
{

        this.openFileDialog1.FileName = System.IO.Path.GetDirectoryName(this.lstFiles.SelectedItem.ToString());

        string openFileName;

        openFileName = this.openFileDialog1.FileName;

        try
        {
            System.Diagnostics.Process.Start(openFileName);

            this.btnOpenThreeFile.Enabled = false;
        }
        catch (Exception ex)
        {
            MessageBox.Show(ex.Message, "错误提示", MessageBoxButtons.OK, MessageBoxIcon.Error);
        }

    }


            问题：为什么openFileName 获取不了lstFiles的值？
            哪里错了啊？
            ![图片说明](https://img-ask.csdn.net/upload/201710/10/1507647142_924343.jpg)

this.openFileDialog1.FileName 这个有值么