C#里面中将字符串转为变量名

例如

string str = "spp";

string spp = "very good";

怎样搞 str 而得到 very good 这个值？

 public partial class Form1 : Form

    {

        string str = "spp";

        public string spp = "very good";

        public Form1()

        {

            InitializeComponent();

            MessageBox.Show(this.GetType().GetField(str).GetValue(this).ToString());

        }

    }