Display a Combobox in a PropertyGrid

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.ComponentModel;

namespace AA
{
    public  class ParameterProperty
    {
        [Category("Parameter Info"), ReadOnlyAttribute(true)]
        public  string Query_ID { get; set; }
        [Category("Parameter Info"), ReadOnlyAttribute(true)]
        public string Parameter_Name { get; set; }
        [Category("Parameter Info"), ReadOnlyAttribute(true)]
        public bool Required { get; set; }
        [Category("Parameter Info"), ReadOnlyAttribute(true)]
        public string Parameter_ID { get; set; }
        [Category("Parameter Info"), ReadOnlyAttribute(true)]
        public int Identity { get; set; }

        [Category("Display")]
        public  int Sequence { get; set; }
        [Category("Display")]
        public  string Label { get; set; }
        [Category("Data")]
        public string Datatype { get; set; }
        [Category("Data")]
        public string Value_1 { get; set; }
        [Category("Data")]
        public string Value_2 { get; set; }
        [Category("Data")]
        public string Operant { get; set;}
        public string[] _Operants = new string[] { "=", ">", "<", "!=" };
       


           
        }
      

    }

ParameterProperty p = new ParameterProperty();
 string s = row["Required"].ToString();
                        p.Query_ID = "A";
                        p.Parameter_ID = 1;
                        p.Sequence = 1;
                        p.Parameter_Name = "A";
                     
                        p.Value_1 = "A";;
                        p.Operant = "A";
                        p.Value_2 = "A";
                        p.Identity = 1
                        propertyGrid1.SelectedObject = p;