private Collection<UserControl2> stringsValue = new Collection<UserControl2>();
        [DesignerSerializationVisibility(
            DesignerSerializationVisibility.Content)]
        public Collection<UserControl2> Strings
        {
            get
            {
                return this.stringsValue;
            }
            set
            {
                this.stringsValue = value;
            }        }会自动产生变量但是删除后不会自动删除,,导致越来越多的没用变量。。