public string Folder
        {
            get
            {
                return _Folder;
            }
            private set
            {
                this._Folder = value;
            }
        }

        private AAA aaa;
        private void button1_Click(object sender, EventArgs e)
        {
            aaa = new AAA();
            aaa.Folder = "ASDFG";
            propertyGrid1.SelectedObject = aaa;
        }

        public class AAA
        {
            private string _Folder;
            [ReadOnly(true)]
            [Description("Folder")]
            [Category("Files")]
            [DefaultValue("")]
            public string Folder
            {
                get
                {
                    return _Folder;
                }
                set
                {
                    this._Folder = value;
                }
            }

        }