csharp MyBindableCustomPicker / Xamarin.Forms

Posted 2021-05-12

using System;
using System.Collections;
using System.Collections.Specialized;
using Xamarin.Forms;

namespace Miso.SearchForms.Controls
{
	/// <summary>
	/// Bindable Custom Picker
	/// 
	/// Xamarin.Forms 2.3.4がでれば、そっちを使った方が良い
	/// </summary>
	public class CustomPicker : Picker
	{
		public CustomPicker()
		{
			//TODO: OnPropertyChangedの"SelectedIndex"でいけるかどうか？
			this.SelectedIndexChanged += CustomPicker_SelectedIndexChanged;
		}

		public static readonly BindableProperty ItemsSourceProperty =
			BindableProperty.Create(nameof(ItemsSource), typeof(IList), typeof(CustomPicker), default(IList),
									propertyChanged: OnItemsSourceChanged);

		public static readonly BindableProperty SelectedItemProperty =
			BindableProperty.Create(nameof(SelectedItem), typeof(object), typeof(CustomPicker), null, BindingMode.TwoWay,
									propertyChanged: OnSelectedItemChanged);

		public IList ItemsSource
		{
			get { return (IList)GetValue(ItemsSourceProperty); }
			set { SetValue(ItemsSourceProperty, value); }
		}

		public object SelectedItem
		{
			get { return GetValue(SelectedItemProperty); }
			set { SetValue(SelectedItemProperty, value); }
		}

		private void CustomPicker_SelectedIndexChanged(object sender, EventArgs e)
		{
			var itemsSource = this.ItemsSource;
			if (itemsSource == null || itemsSource.Count == 0)
				return;
		
			this.SelectedItem = (itemsSource.Count >= this.SelectedIndex + 1) ? itemsSource[this.SelectedIndex] : null;
		}
		private static void OnItemsSourceChanged(BindableObject bindable, object oldValue, object newValue)
		{
			OnItemsSourceChanged(((CustomPicker)bindable), (IList)oldValue, (IList)newValue);
		}

		private static void OnItemsSourceChanged(CustomPicker picker, IList oldValue, IList newValue)
		{
			picker.Items.Clear();

			if (newValue == null)
				return;

			NotifyCollectionChangedEventHandler handler = (sender, e) => CollectionChanged(picker, e);

			var oldObservable = oldValue as INotifyCollectionChanged;
			if (oldObservable != null)
			{
				oldObservable.CollectionChanged -= handler;
			}

			var newObservable = newValue as INotifyCollectionChanged;
			if (newObservable != null)
			{
				newObservable.CollectionChanged += handler;
			}

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

		static void CollectionChanged(CustomPicker picker, NotifyCollectionChangedEventArgs e)
		{
			switch (e.Action)
			{
				case NotifyCollectionChangedAction.Add:
					AddItems(picker, e);
					break;
				case NotifyCollectionChangedAction.Remove:
					throw new NotImplementedException();
				default: //Move, Replace, Reset
					picker.Items.Clear();
					picker.SelectedItem = null;
					break;
			}
		}
		private static void OnSelectedItemChanged(BindableObject bindable, object oldValue, object newValue)
		{
			OnSelectedItemChanged((CustomPicker)bindable, oldValue, newValue);
		}

		private static void OnSelectedItemChanged(CustomPicker picker, object oldValue, object newValue)
		{
			if (picker.ItemsSource == null)
			{
				throw new Exception("ItemSource is null");
			}
			if (newValue == null)
			{
				picker.SelectedIndex = -1;
				return;
			}
			picker.SelectedIndex = picker.ItemsSource.IndexOf(newValue);
			return;
		}
		private static void AddItems(CustomPicker picker, NotifyCollectionChangedEventArgs e)
		{
			int index = e.NewStartingIndex < 0 ? picker.Items.Count : e.NewStartingIndex;
			foreach (object newItem in e.NewItems)
				picker.Items.Insert(index++, newItem.ToString());
		}

	}
}