An ObservableDictionary<TKey, TValue>

ObservableDictionary.cs

using System;
using System.Collections;
using System.Collections.Generic;
using System.Collections.Specialized;
using System.ComponentModel;
using System.Diagnostics;
using System.Dynamic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace Xamarin.Forms.Dynamic
{
	/// <summary>
	/// Provides a dictionary for use with data binding.
	/// </summary>
	/// <typeparam name="TKey">Specifies the type of the keys in this collection.</typeparam>
	/// <typeparam name="TValue">Specifies the type of the values in this collection.</typeparam>
	[DebuggerDisplay ("Count={Count}")]
	public class ObservableDictionary<TKey, TValue> : 
		ICollection<KeyValuePair<TKey, TValue>>, IDictionary<TKey, TValue>,
		INotifyCollectionChanged, INotifyPropertyChanged
	{
		readonly IDictionary<TKey, TValue> dictionary;

		/// <summary>Event raised when the collection changes.</summary>
		public event NotifyCollectionChangedEventHandler CollectionChanged = (sender, args) => { };

		/// <summary>Event raised when a property on the collection changes.</summary>
		public event PropertyChangedEventHandler PropertyChanged = (sender, args) => { };

		/// <summary>
		/// Initializes an instance of the class.
		/// </summary>
		public ObservableDictionary ()
			: this (new Dictionary<TKey, TValue> ())
		{
		}

		/// <summary>
		/// Initializes an instance of the class using another dictionary as 
		/// the key/value store.
		/// </summary>
		public ObservableDictionary (IDictionary<TKey, TValue> dictionary)
		{
			this.dictionary = dictionary;
		}

		void AddWithNotification (KeyValuePair<TKey, TValue> item)
		{
			AddWithNotification (item.Key, item.Value);
		}

		void AddWithNotification (TKey key, TValue value)
		{
			dictionary.Add (key, value);

			CollectionChanged (this, new NotifyCollectionChangedEventArgs (NotifyCollectionChangedAction.Add,
				new KeyValuePair<TKey, TValue> (key, value)));
			PropertyChanged (this, new PropertyChangedEventArgs ("Count"));
			PropertyChanged (this, new PropertyChangedEventArgs ("Keys"));
			PropertyChanged (this, new PropertyChangedEventArgs ("Values"));
		}

		bool RemoveWithNotification (TKey key)
		{
			TValue value;
			if (dictionary.TryGetValue (key, out value) && dictionary.Remove (key)) {
				CollectionChanged (this, new NotifyCollectionChangedEventArgs (NotifyCollectionChangedAction.Remove,
					new KeyValuePair<TKey, TValue> (key, value)));
				PropertyChanged (this, new PropertyChangedEventArgs ("Count"));
				PropertyChanged (this, new PropertyChangedEventArgs ("Keys"));
				PropertyChanged (this, new PropertyChangedEventArgs ("Values"));

				return true;
			}

			return false;
		}

		void UpdateWithNotification (TKey key, TValue value)
		{
			TValue existing;
			if (dictionary.TryGetValue (key, out existing)) {
				dictionary[key] = value;

				CollectionChanged (this, new NotifyCollectionChangedEventArgs (NotifyCollectionChangedAction.Replace,
					new KeyValuePair<TKey, TValue> (key, value),
					new KeyValuePair<TKey, TValue> (key, existing)));
				PropertyChanged (this, new PropertyChangedEventArgs ("Values"));
			} else {
				AddWithNotification (key, value);
			}
		}

		/// <summary>
		/// Allows derived classes to raise custom property changed events.
		/// </summary>
		protected void RaisePropertyChanged(PropertyChangedEventArgs args)
		{
			PropertyChanged (this, args);
		}

		#region IDictionary<TKey,TValue> Members

		/// <summary>
		/// Adds an element with the provided key and value to the <see cref="T:System.Collections.Generic.IDictionary`2" />.
		/// </summary>
		/// <param name="key">The object to use as the key of the element to add.</param>
		/// <param name="value">The object to use as the value of the element to add.</param>
		public void Add (TKey key, TValue value)
		{
			AddWithNotification (key, value);
		}

		/// <summary>
		/// Determines whether the <see cref="T:System.Collections.Generic.IDictionary`2" /> contains an element with the specified key.
		/// </summary>
		/// <param name="key">The key to locate in the <see cref="T:System.Collections.Generic.IDictionary`2" />.</param>
		/// <returns>
		/// true if the <see cref="T:System.Collections.Generic.IDictionary`2" /> contains an element with the key; otherwise, false.
		/// </returns>
		public bool ContainsKey (TKey key)
		{
			return dictionary.ContainsKey (key);
		}

		/// <summary>
		/// Gets an <see cref="T:System.Collections.Generic.ICollection`1" /> containing the keys of the <see cref="T:System.Collections.Generic.IDictionary`2" />.
		/// </summary>
		/// <returns>An <see cref="T:System.Collections.Generic.ICollection`1" /> containing the keys of the object that implements <see cref="T:System.Collections.Generic.IDictionary`2" />.</returns>
		public ICollection<TKey> Keys
		{
			get { return dictionary.Keys; }
		}

		/// <summary>
		/// Removes the element with the specified key from the <see cref="T:System.Collections.Generic.IDictionary`2" />.
		/// </summary>
		/// <param name="key">The key of the element to remove.</param>
		/// <returns>
		/// true if the element is successfully removed; otherwise, false.  This method also returns false if <paramref name="key" /> was not found in the original <see cref="T:System.Collections.Generic.IDictionary`2" />.
		/// </returns>
		public bool Remove (TKey key)
		{
			return RemoveWithNotification (key);
		}

		/// <summary>
		/// Gets the value associated with the specified key.
		/// </summary>
		/// <param name="key">The key whose value to get.</param>
		/// <param name="value">When this method returns, the value associated with the specified key, if the key is found; otherwise, the default value for the type of the <paramref name="value" /> parameter. This parameter is passed uninitialized.</param>
		/// <returns>
		/// true if the object that implements <see cref="T:System.Collections.Generic.IDictionary`2" /> contains an element with the specified key; otherwise, false.
		/// </returns>
		public bool TryGetValue (TKey key, out TValue value)
		{
			return dictionary.TryGetValue (key, out value);
		}

		/// <summary>
		/// Gets an <see cref="T:System.Collections.Generic.ICollection`1" /> containing the values in the <see cref="T:System.Collections.Generic.IDictionary`2" />.
		/// </summary>
		/// <returns>An <see cref="T:System.Collections.Generic.ICollection`1" /> containing the values in the object that implements <see cref="T:System.Collections.Generic.IDictionary`2" />.</returns>
		public ICollection<TValue> Values
		{
			get { return dictionary.Values; }
		}

		/// <summary>
		/// Gets or sets the element with the specified key.
		/// </summary>
		/// <param name="key">The key.</param>
		/// <returns></returns>
		public TValue this[TKey key]
		{
			get { return dictionary[key]; }
			set { UpdateWithNotification (key, value); }
		}

		#endregion

		#region ICollection<KeyValuePair<TKey,TValue>> Members

		void ICollection<KeyValuePair<TKey, TValue>>.Add (KeyValuePair<TKey, TValue> item)
		{
			AddWithNotification (item);
		}

		void ICollection<KeyValuePair<TKey, TValue>>.Clear ()
		{
			((ICollection<KeyValuePair<TKey, TValue>>)dictionary).Clear ();

			CollectionChanged (this, new NotifyCollectionChangedEventArgs (NotifyCollectionChangedAction.Reset));
			PropertyChanged (this, new PropertyChangedEventArgs ("Count"));
			PropertyChanged (this, new PropertyChangedEventArgs ("Keys"));
			PropertyChanged (this, new PropertyChangedEventArgs ("Values"));
		}

		bool ICollection<KeyValuePair<TKey, TValue>>.Contains (KeyValuePair<TKey, TValue> item)
		{
			return ((ICollection<KeyValuePair<TKey, TValue>>)dictionary).Contains (item);
		}

		void ICollection<KeyValuePair<TKey, TValue>>.CopyTo (KeyValuePair<TKey, TValue>[] array, int arrayIndex)
		{
			((ICollection<KeyValuePair<TKey, TValue>>)dictionary).CopyTo (array, arrayIndex);
		}

		int ICollection<KeyValuePair<TKey, TValue>>.Count
		{
			get { return ((ICollection<KeyValuePair<TKey, TValue>>)dictionary).Count; }
		}

		bool ICollection<KeyValuePair<TKey, TValue>>.IsReadOnly
		{
			get { return ((ICollection<KeyValuePair<TKey, TValue>>)dictionary).IsReadOnly; }
		}

		bool ICollection<KeyValuePair<TKey, TValue>>.Remove (KeyValuePair<TKey, TValue> item)
		{
			return RemoveWithNotification (item.Key);
		}

		#endregion

		#region IEnumerable<KeyValuePair<TKey,TValue>> Members

		IEnumerator<KeyValuePair<TKey, TValue>> IEnumerable<KeyValuePair<TKey, TValue>>.GetEnumerator ()
		{
			return ((ICollection<KeyValuePair<TKey, TValue>>)dictionary).GetEnumerator ();
		}

		IEnumerator IEnumerable.GetEnumerator ()
		{
			return ((ICollection<KeyValuePair<TKey, TValue>>)dictionary).GetEnumerator ();
		}

		#endregion
	}
}