Event Handler in MonoTouch not allowing objects to be collected

UIDateFieldTestViewController.cs

using System;
using System.Drawing;

using MonoTouch.Foundation;
using MonoTouch.UIKit;

namespace UIDateFieldTest
{
    public partial class UIDateFieldTestViewController : UIViewController
    {
        public UIDateFieldTestViewController() : base ("UIDateFieldTestViewController", null)
        {
        }

        public override void DidReceiveMemoryWarning()
        {
            // Releases the view if it doesn't have a superview.
            base.DidReceiveMemoryWarning();

            // Release any cached data, images, etc that aren't in use.
        }

        public override void ViewDidLoad()
        {
            base.ViewDidLoad();


            // Perform any additional setup after loading the view, typically from a nib.
        }

        public override void ViewDidUnload()
        {
            base.ViewDidUnload();

            // Clear any references to subviews of the main view in order to
            // allow the Garbage Collector to collect them sooner.
            //
            // e.g. myOutlet.Dispose (); myOutlet = null;

            ReleaseDesignerOutlets();
        }

        public override bool ShouldAutorotateToInterfaceOrientation(UIInterfaceOrientation toInterfaceOrientation)
        {
            // Return true for supported orientations
            return (toInterfaceOrientation != UIInterfaceOrientation.PortraitUpsideDown);
        }

        partial void buttonClicked(MonoTouch.Foundation.NSObject sender)
        {
            var tbView = new UITableViewController();
            tbView.TableView.DataSource = new TestSource();


            this.NavigationController.PushViewController(tbView, true);

        }
    }

    public class TestSource : UITableViewDataSource
    {
        public override int NumberOfSections(UITableView tableView)
        {
            return 1;
        }

        public override int RowsInSection(UITableView tableView, int section)
        {
            return 2;
        }

        public override UITableViewCell GetCell(UITableView tableView, NSIndexPath indexPath)
        {
            if (indexPath.Row == 0)
            {
                var cell1 = tableView.DequeueReusableCell(new NSString("Cell1"));
                if (cell1 == null)
                {
                    cell1 = new TextInputTableViewCell(UITableViewCellStyle.Default, new NSString("Cell1"));
                }
                return cell1;
            }

            var cell2 = tableView.DequeueReusableCell(new NSString("Cell2"));
            if (cell2 == null)
            {
                cell2 = new DateInputTableViewCell(UITableViewCellStyle.Default, new NSString("Cell2"));
            }
            return cell2;
        }
    }



    public class TextInputTableViewCell : UITableViewCell
    {
        private UITextField textField;

        public TextInputTableViewCell(UITableViewCellStyle style, NSString reuseIdentifer)
            : base(style, reuseIdentifer)
        {
            this.ConfigureCell();
        }

        public UITextField TextField
        {
            get
            {
                return this.textField;
            }
        }

        protected override void Dispose (bool disposing)
        {
            Console.WriteLine("dispose textField {0}", disposing);
            if (disposing)
            {
                this.textField.Dispose();
                this.textField = null;
            }

            base.Dispose (disposing);
        }

        protected void ConfigureCell ()
        {
            this.SelectionStyle = UITableViewCellSelectionStyle.None;

            this.textField = new UITextField(this.CalculateTextFieldFrame(string.Empty))
            {
                VerticalAlignment = UIControlContentVerticalAlignment.Center,
                ClearButtonMode = UITextFieldViewMode.WhileEditing,
            };

            this.textField.Font = UIFont.SystemFontOfSize(17);
            this.textField.AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleLeftMargin;

            this.ContentView.AddSubview(this.textField);

            this.textField.Ended += this.TextValueChanged;
        }

        private void TextValueChanged(object sender, EventArgs args)
        {
        }

        private RectangleF CalculateTextFieldFrame(string textValue)
        {
            float margin = 10;

            var textSize = new RectangleF (margin, 10, this.ContentView.Bounds.Width - (margin * 2), this.ContentView.Bounds.Height - (margin * 2));

            if (!String.IsNullOrEmpty(textValue))
            {
                var sz = this.CalculateEntrySize(null);
                textSize = new RectangleF (sz.Width, (this.ContentView.Bounds.Height - sz.Height) / 2 - 1, sz.Width * 2 - margin, sz.Height);
            }

            return textSize;
        }

        private SizeF CalculateEntrySize (UITableView tv)
        {
            var sz = this.StringSize("W", UIFont.SystemFontOfSize (17));
            float w = this.ContentView.Bounds.Width / 3;

            return new SizeF(w, sz.Height);
        }
    }






    public class DateInputTableViewCell : UITableViewCell
    {
        private UIDateField dateField;

        public DateInputTableViewCell(UITableViewCellStyle style, NSString reuseIdentifer)
            : base(style, reuseIdentifer)
        {
            this.ConfigureCell();
        }

        protected override void Dispose (bool disposing)
        {
            Console.WriteLine("dispose ..{0}", disposing);
            if (disposing)
            {
                this.dateField.Dispose();
                this.dateField = null;
            }

            base.Dispose (disposing);
        }

        protected void ConfigureCell ()
        {
            this.SelectionStyle = UITableViewCellSelectionStyle.None;

            this.dateField = new UIDateField(this.CalculateTextFieldFrame(string.Empty))
            {
                AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleLeftMargin,
            };

            this.ContentView.AddSubview(this.dateField);

            // FIXME: More investigation required here, hooking this handler up causes the datefield and the table cell to be not collected
            this.dateField.ValueChanged += this.DateValueChanged;
        }

        private void DateValueChanged(object sender, EventArgs args)
        {
        }

        private RectangleF CalculateTextFieldFrame(string textValue)
        {
            float margin = 10;

            var textSize = new RectangleF (margin, 10, this.ContentView.Bounds.Width - (margin * 2), this.ContentView.Bounds.Height - (margin * 2));

            if (!String.IsNullOrEmpty(textValue))
            {
                var sz = this.CalculateEntrySize(null);
                textSize = new RectangleF (sz.Width, (this.ContentView.Bounds.Height - sz.Height) / 2 - 1, sz.Width * 2 - margin, sz.Height);
            }

            return textSize;
        }

        private SizeF CalculateEntrySize (UITableView tv)
        {
            var sz = this.StringSize("W", UIFont.SystemFontOfSize (17));
            float w = this.ContentView.Bounds.Width / 3;

            return new SizeF(w, sz.Height);
        }
    }


    public class UIDateField : UIControl
    {
        private DateTime date;
        private UIDatePicker picker;
        private UILabel label;
        private string dateFormat;
        private UIView accessoryView;

        public UIDateField(RectangleF frame) : base(frame)
        {
            this.dateFormat = "D";

            this.picker = new UIDatePicker();
            this.picker.Mode = UIDatePickerMode.Date;
            this.picker.TimeZone = NSTimeZone.FromAbbreviation("GMT");
            this.picker.ValueChanged += this.PickerValueChanged;

            this.label = new UILabel(this.Bounds);
            this.label.AutoresizingMask = UIViewAutoresizing.FlexibleWidth | UIViewAutoresizing.FlexibleLeftMargin;
            this.label.BackgroundColor = UIColor.Green;
            this.label.UserInteractionEnabled = false;
            this.AddSubview(this.label);

            this.Date = DateTime.Today;
        }

        ~UIDateField()
        {
            Console.WriteLine("UIDateField");
        }

        public override bool CanBecomeFirstResponder
        {
            get
            {
                return this.Enabled;
            }
        }

        public override UIView InputView
        {
            get
            {
                return this.picker;
            }
        }

        [Export("inputAccessoryView")]
        public new UIView InputAccessoryView
        {
            get
            {
                return this.accessoryView;
            }

            set
            {
                this.accessoryView = value;
            }
        }

        public DateTime Date
        {
            get
            {
                return this.date;
            }

            set
            {
                if (value != this.date)
                {
                    this.date = value;
                    this.picker.Date = DateTime.SpecifyKind(value, DateTimeKind.Utc);
                    this.label.Text = this.date.ToString(this.DateFormat);
                }
            }
        }

        public string DateFormat
        {
            get
            {
                return this.dateFormat;
            }

            set
            {
                this.dateFormat = value;
                this.label.Text = this.date.ToString(this.DateFormat);
            }
        }

        public override void TouchesEnded(MonoTouch.Foundation.NSSet touches, UIEvent evt)
        {
            base.TouchesEnded(touches, evt);
            if (evt.Type == UIEventType.Touches)
            {
                if (this.IsFirstResponder)
                {
                    this.ResignFirstResponder();
                }
                else
                {
                    this.BecomeFirstResponder();
                }
            }
        }

        protected override void Dispose(bool disposing)
        {
            Console.WriteLine("dispose UIDateField");
            if (disposing)
            {
                this.picker.Dispose();
                this.picker = null;
                this.label.Dispose();
                this.label = null;
            }

            base.Dispose(disposing);
        }

        private void PickerValueChanged(object sender, EventArgs args)
        {
            this.Date = DateTime.SpecifyKind(this.picker.Date, DateTimeKind.Unspecified);
            this.SendActionForControlEvents(UIControlEvent.ValueChanged);
        }
    }

}