public class CustomGrid : RadGridView
        {
            public override string ThemeClassName
            {
                get
                {
                    return typeof(RadGridView).FullName;
                }
            }
            protected override void OnMouseDown(MouseEventArgs e)
            {
                GridExpanderItem expander = this.ElementTree.GetElementAtPoint(e.Location) as GridExpanderItem;
                if (expander != null)
                {
                    flag = true;
                }
                base.OnMouseDown(e);
            }

            protected override void OnMouseUp(MouseEventArgs e)
            {
                base.OnMouseUp(e);
                flag = false;
            }

            bool flag = false;

            protected override void OnPageChanging(object sender, PageChangingEventArgs e)
            {
                if (flag)
                {
                    e.Cancel = true;
                }
                base.OnPageChanging(sender, e);

            }
        }