public partial class ViewController : UIViewController
    {
        private C1CollectionView<Item> cv;
        public ViewController(IntPtr handle) : base(handle)
        {
        }
        public override void ViewDidLoad()
        {
            base.ViewDidLoad();
            // Perform any additional setup after loading the view, typically from a nib.
            sunburst = new C1Sunburst();
            sunburst.Binding = "Value";
            sunburst.BindingName = "Year,Quarter,Month";
            sunburst.ToolTipContent = "{}{name}\n{y}";
            sunburst.DataLabel.Position = PieLabelPosition.Center;
            sunburst.DataLabel.Content = "{}{name}";
            cv = DataService.CreateGroupCVData();
            this.Add(sunburst);

            cv.GroupChanged += View_GroupChanged;
            cv.SortChanged += Cv_SortChanged;

            //Sort cannot work synchronize with group in current CollectionView
            SortDescription yearSortDescription = new SortDescription("Year", SortDirection.Ascending);
            SortDescription quarterSortDescription = new SortDescription("Quarter", SortDirection.Ascending);
            SortDescription monthSortDescription = new SortDescription("MonthValue", SortDirection.Ascending);
            SortDescription[] sortDescriptions = new SortDescription[] { yearSortDescription, quarterSortDescription, monthSortDescription };
            cv.SortAsync(sortDescriptions);
        }
        private void Cv_SortChanged(object sender, System.EventArgs e)
        {
            GroupDescription yearGroupDescription = new GroupDescription("Year");
            GroupDescription quarterGroupDescription = new GroupDescription("Quarter");
            GroupDescription monthGroupDescription = new GroupDescription("MonthName");
            GroupDescription[] groupDescriptions = new GroupDescription[] { yearGroupDescription, quarterGroupDescription, monthGroupDescription };
            cv.GroupAsync(groupDescriptions);
        }

        private void View_GroupChanged(object sender, System.EventArgs e)
        {
            this.sunburst.ItemsSource = cv;
            CGRect rect = new CGRect(this.View.Frame.X, this.View.Frame.Y + 80,
                                     this.View.Frame.Width, this.View.Frame.Height - 80);

            sunburst.Frame = new CGRect(rect.X, rect.Y, rect.Width, rect.Height - 10);
        }
        public override void ViewDidLayoutSubviews()
        {
            base.ViewDidLayoutSubviews();

            sunburst.Frame = new CGRect(this.View.Frame.X, this.View.Frame.Y,
                                     this.View.Frame.Width, this.View.Frame.Height);
        }