This custom picker resolves one issue (issue :- User can't be able to handle done button in default iOS Picker) in Xamarin forms.

Xamarin-Forms-iOS-BindablePicker.cs

namespace CustomControl
{
    public class BindablePicker : Picker
    {
        #region Fields

        //Bindable property for the items source
        public static readonly BindableProperty ItemsSourceProperty =
            BindableProperty.Create<BindablePicker, IEnumerable>(p => p.ItemsSource, null, propertyChanged: OnItemsSourcePropertyChanged);

        //Bindable property for the selected item
        public static readonly BindableProperty SelectedItemProperty =
            BindableProperty.Create<BindablePicker, object>(p => p.SelectedItem, null, BindingMode.TwoWay, propertyChanged: OnSelectedItemPropertyChanged);

        #endregion

        public BindablePicker() {
            if (Device.OS == TargetPlatform.iOS)
            {
                this.Unfocused += OnUnfocused;
            }
            else {
                this.SelectedIndexChanged += OnSelectedIndexChanged;
            }
        }

        void OnUnfocused(object sender, FocusEventArgs args) {
            OnSelectedIndexChanged(sender,args);
        }
        void OnSelectedIndexChanged(object sender,EventArgs args) {
            var picker = (BindablePicker)sender;
            if (picker != null && picker.ItemsSource != null)
                picker.SelectedItem = picker.Items[picker.SelectedIndex];
        }
        #region Properties

        /// <summary>
        /// Gets or sets the items source.
        /// </summary>
        /// <value>
        /// The items source.
        /// </value>
        public IEnumerable ItemsSource
        {
            get { return (IEnumerable)GetValue(ItemsSourceProperty); }
            set { SetValue(ItemsSourceProperty, value); }
        }

        /// <summary>
        /// Gets or sets the selected item.
        /// </summary>
        /// <value>
        /// The selected item.
        /// </value>
        public object SelectedItem
        {
            get { return GetValue(SelectedItemProperty); }
            set { SetValue(SelectedItemProperty, value); }
        }

        #endregion

        #region Methods

        /// <summary>
        /// Called when [items source property changed].
        /// </summary>
        /// <param name="bindable">The bindable.</param>
        /// <param name="value">The value.</param>
        /// <param name="newValue">The new value.</param>
        private static void OnItemsSourcePropertyChanged(BindableObject bindable, IEnumerable value, IEnumerable newValue)
        {
            var picker = (BindablePicker)bindable;
            var notifyCollection = newValue as INotifyCollectionChanged;
            if (notifyCollection != null)
            {
                notifyCollection.CollectionChanged += (sender, args) =>
                {
                    if (args.NewItems != null)
                    {
                        foreach (var newItem in args.NewItems)
                        {
                            picker.Items.Add((newItem ?? "").ToString());
                        }
                    }
                    if (args.OldItems != null)
                    {
                        foreach (var oldItem in args.OldItems)
                        {
                            picker.Items.Remove((oldItem ?? "").ToString());
                        }
                    }
                };
            }

            if (newValue == null)
                return;

            picker.Items.Clear();

            foreach (var item in newValue)
                picker.Items.Add((item ?? "").ToString());
        }

        /// <summary>
        /// Called when [selected item property changed].
        /// </summary>
        /// <param name="bindable">The bindable.</param>
        /// <param name="value">The value.</param>
        /// <param name="newValue">The new value.</param>
        private static void OnSelectedItemPropertyChanged(BindableObject bindable, object value, object newValue)
        {
            var picker = (BindablePicker)bindable;
            if (picker.ItemsSource != null)
                picker.SelectedIndex = picker.ItemsSource.IndexOf(picker.SelectedItem);
        }

        #endregion
    }
    public static class EnumerableExtensions
    {
        /// <summary>
        /// Returns the index of the specified object in the collection.
        /// </summary>
        /// <param name="self">The self.</param>
        /// <param name="obj">The object.</param>
        /// <returns>If found returns index otherwise -1</returns>
        public static int IndexOf(this IEnumerable self, object obj)
        {
            int index = -1;

            var enumerator = self.GetEnumerator();
            enumerator.Reset();
            int i = 0;
            while (enumerator.MoveNext())
            {
                if (enumerator.Current == obj)
                {
                    index = i;
                    break;
                }

                i++;
            }

            return index;
        }
    }
}