C#通过文件路径截取对应的文件夹路径

 try
            {
                OpenFileDialog openFileDialog = new OpenFileDialog();
                string str = comboBox_hexFilePath.Text;
                string file = str.Substring(, str.LastIndexOf("\\") + );//去掉了路径
                openFileDialog.InitialDirectory = file;

                openFileDialog.Filter = "Hex文件|*.hex";
                openFileDialog.RestoreDirectory = true;
                openFileDialog.FilterIndex = ;

                    comboBox_hexFilePath.Text = openFileDialog.FileName;//文件名

                }
            }
            catch
            {
                show_info("hex文件选择..");
            }