combox已绑定，如何通过ValueMember找到对应的哪项？求解

            DataTable data = new DataTable();            data.Columns.Add("column1", typeof(int));            data.Columns.Add("column2", typeof(string));            DataRow dr1 = data.NewRow();            dr1["column1"] = 1;            dr1["column2"] = "NO.1";            DataRow dr2 = data.NewRow();            dr2["column1"] = 2;            dr2["column2"] = "NO.2";            DataRow dr3 = data.NewRow();            dr3["column1"] = 3;            dr3["column2"] = "NO.3";            DataRow dr4 = data.NewRow();             data.Rows.Add(dr1);            data.Rows.Add(dr2);            data.Rows.Add(dr3);            this.comboBox1.DataSource = data;            this.comboBox1.DisplayMember = "column2";            this.comboBox1.ValueMember = "column2";