Question

I’ve searched the interwebs to no avail… I am using MT.D and want to set a birthdate for a person using the DateElement, but the birthdate could be null, meaning that the data has not been collected yet. Anyone know how to make a DateElement accept a null value OR a date?

Answer 1

UPDATE 20140106: Since iOS7 has been released, Apple desires that date/time pickers be inline with content rather than be an action sheet, or in this case, full screen overlay. Therefore, this code is for how-to and historical purposes only.

Ok, so I rolled my own class. Personally I think the current date/time picker set up doesn’t look as professional as having the equivalent of an ActionSheet pop up with a datepicker attached to it. Someone more experienced in MT.D may be able to figure it out, but what I did was to copy the code from DateTimeElement and DateElement and modify it so that it has three buttons on top: The left-most button is Cancel, the right button area has “Set” and “Null” buttons. The captions for the right buttons can be set to whatever you like in the ctor of the class, but can be defaulted to “Set Date” and “No Date”.

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NULLABLE DATE TIME ELEMENT

using MonoTouch.Foundation;
using MonoTouch.UIKit;
using System;
using System.Drawing;

namespace MonoTouch.Dialog
{
    public class NullableDateTimeElement : StringElement
    {
        private class MyViewController : UIViewController
        {
            private NullableDateTimeElement container;
            private bool hasNullValue = false;
            private bool hasBeenSet = false;
            //private EventHandler nullButtonTouched;
            //UIButton isNullButton;
            public bool Autorotate
            {
                get;
                set;
            }
            public MyViewController (NullableDateTimeElement container)
            {
                this.container = container;
            }
            public override void ViewDidLoad ()
            {
                base.ViewDidLoad ();
                //isNullButton = UIButton.FromType (UIButtonType.RoundedRect);
                //isNullButton.SizeToFit ();
                //isNullButton.Frame = new RectangleF(this.View.Frame.Top, this.View.Frame.Left, this.View.Frame.Width - 40f, 40f);
                //isNullButton.SetTitle (container.NullButtonCaption, UIControlState.Normal);
                this.NavigationItem.RightBarButtonItems = new UIBarButtonItem[]
                {
                    new UIBarButtonItem(container.NullButtonCaption, UIBarButtonItemStyle.Done, NullButtonTapped),
                    new UIBarButtonItem(container.SetButtonCaption, UIBarButtonItemStyle.Done, SetButtonTapped)
                };
                this.NavigationItem.LeftBarButtonItem = new UIBarButtonItem(UIBarButtonSystemItem.Cancel, CancelTapped);
                this.NavigationItem.HidesBackButton = true;
                //this.View.AddSubview (isNullButton);
                //this.isNullButton.TouchUpInside += (nullButtonTouched = new EventHandler(nullButtonWasTouched)); 
            }

            void CancelTapped(object sender, EventArgs e)
            {
                hasBeenSet = false;
                this.NavigationController.PopViewControllerAnimated (true);
            }

            void NullButtonTapped(object sender, EventArgs e)
            {
                hasBeenSet = true;
                hasNullValue = true;
                this.NavigationController.PopViewControllerAnimated (true);
            }

            void SetButtonTapped(object sender, EventArgs e)
            {
                hasBeenSet = true;
                hasNullValue = false;
                this.NavigationController.PopViewControllerAnimated (true);
            }

            public override void ViewWillDisappear (bool animated)
            {
                base.ViewWillDisappear (animated);
                if (hasBeenSet)
                {
                    if (!hasNullValue)
                        this.container.DateValue = this.container.datePicker.Date;
                    else
                        this.container.DateValue = null;
                }
                //this.isNullButton.TouchUpInside -= nullButtonTouched;
                //nullButtonTouched = null;
            }
            /*void nullButtonWasTouched(object sender, EventArgs e)
            {
                hasNullValue = true;
                NavigationController.PopViewControllerAnimated (true);
            }*/
            public override void DidRotate (UIInterfaceOrientation fromInterfaceOrientation)
            {
                base.DidRotate (fromInterfaceOrientation);
                this.container.datePicker.Frame = NullableDateTimeElement.PickerFrameWithSize (this.container.datePicker.SizeThatFits (SizeF.Empty));
            }
            public override bool ShouldAutorotateToInterfaceOrientation (UIInterfaceOrientation toInterfaceOrientation)
            {
                return this.Autorotate;
            }
        }
        public DateTime? DateValue;
        public UIDatePicker datePicker;
        //public UIButton isNullButton;
        public string NullButtonCaption { get; set; }
        public string SetButtonCaption { get; set; }

        protected internal NSDateFormatter fmt = new NSDateFormatter
        {
            DateStyle = NSDateFormatterStyle.Short
        };

        public NullableDateTimeElement (string caption, DateTime? date, string nullButtonCaption, string setButtonCaption) : base (caption)
        {
            this.DateValue = date;
            this.Value = this.FormatDate (date);
            this.NullButtonCaption = nullButtonCaption;
            this.SetButtonCaption = setButtonCaption;
        }

        public NullableDateTimeElement(string caption, DateTime? date, string nullButtonCaption) : this(caption, date, nullButtonCaption, "Set Date")
        {}

        public NullableDateTimeElement(string caption, DateTime? date) : this(caption, date, "No Date", "Set Date")
        {}

        public override UITableViewCell GetCell (UITableView tv)
        {
            this.Value = this.FormatDate (this.DateValue);
            UITableViewCell cell = base.GetCell (tv);
            cell.Accessory = UITableViewCellAccessory.DisclosureIndicator;
            return cell;
        }
        protected override void Dispose (bool disposing)
        {
            base.Dispose (disposing);
            if (disposing)
            {
                if (this.fmt != null)
                {
                    this.fmt.Dispose ();
                    this.fmt = null;
                }
/*              if (this.isNullButton != null)
                {
                    this.isNullButton.Dispose ();
                    this.isNullButton = null;
                }*/
                if (this.datePicker != null)
                {
                    this.datePicker.Dispose ();
                    this.datePicker = null;
                }
            }
        }
        public virtual string FormatDate (DateTime? dt)
        {
            if (dt.HasValue)
                return this.fmt.ToString (dt.Value) + " " + dt.Value.ToLocalTime ().ToShortTimeString ();
            else
                return NullButtonCaption;
        }
        public virtual UIDatePicker CreatePicker ()
        {
            return new UIDatePicker (RectangleF.Empty)
            {
                AutoresizingMask = UIViewAutoresizing.FlexibleWidth,
                Mode = UIDatePickerMode.DateAndTime,
                Date = this.DateValue ?? DateTime.Now
            };
        }
        private static RectangleF PickerFrameWithSize (SizeF size)
        {
            RectangleF applicationFrame = UIScreen.MainScreen.ApplicationFrame;
            float y = 0f;
            float x = 0f;
            switch (UIApplication.SharedApplication.StatusBarOrientation)
            {
                case UIInterfaceOrientation.Portrait:
                case UIInterfaceOrientation.PortraitUpsideDown:

                    {
                        x = (applicationFrame.Width - size.Width) / 2f;
                        y = (applicationFrame.Height - size.Height) / 2f - 25f;
                        break;
                    }
                case UIInterfaceOrientation.LandscapeRight:
                case UIInterfaceOrientation.LandscapeLeft:

                    {
                        x = (applicationFrame.Height - size.Width) / 2f;
                        y = (applicationFrame.Width - size.Height) / 2f - 17f;
                        break;
                    }
            }
            return new RectangleF (x, y, size.Width, size.Height);
        }
        public override void Selected (DialogViewController dvc, UITableView tableView, NSIndexPath path)
        {
            NullableDateTimeElement.MyViewController myViewController = new NullableDateTimeElement.MyViewController (this)
            {
                Autorotate = dvc.Autorotate
            };
            this.datePicker = this.CreatePicker ();
            this.datePicker.Frame = NullableDateTimeElement.PickerFrameWithSize (this.datePicker.SizeThatFits (SizeF.Empty));
            myViewController.View.BackgroundColor = UIColor.Black;
            myViewController.View.AddSubview (this.datePicker);
            dvc.ActivateController (myViewController);
        }
    }
}

NULLABLE DATE-ONLY ELEMENT

using System;
using MonoTouch.Foundation;
using MonoTouch.UIKit;


namespace MonoTouch.Dialog
{
    public class NullableDateElement : NullableDateTimeElement
    {
        public NullableDateElement (string caption, DateTime? date, string nullButtonCaption, string setButtonCaption) : base (caption, date, nullButtonCaption, setButtonCaption)
        {
            initDateOnlyPicker ();
        }

        public NullableDateElement (string caption, DateTime? date, string nullButtonCaption) : base(caption, date, nullButtonCaption)
        {
            initDateOnlyPicker ();
        }

        public NullableDateElement (string caption, DateTime? date) : base(caption, date)
        {
            initDateOnlyPicker ();
        }


        void initDateOnlyPicker()
        {
            this.fmt.DateStyle = NSDateFormatterStyle.Medium;
        }

        public override string FormatDate (DateTime? dt)
        {
            if (dt.HasValue)
                return this.fmt.ToString (dt);
            else
                return base.NullButtonCaption;
        }
        public override UIDatePicker CreatePicker ()
        {
            UIDatePicker uIDatePicker = base.CreatePicker ();
            uIDatePicker.Mode = UIDatePickerMode.Date;
            return uIDatePicker;
        }
    }
}

@Miguel, Please consider adding this to MonoTouch.Dialog, as there is a very legitimate business need for null dates/date times, and this solution seems to do the trick. My code will have to be cleaned up a bit, but this works.