1 files changed, 113 insertions, 0 deletions
diff --git a/Xamarin.Forms.Pages/BaseDataSource.cs b/Xamarin.Forms.Pages/BaseDataSource.cs
new file mode 100644
index 00000000..31608b83
--- /dev/null
+++ b/Xamarin.Forms.Pages/BaseDataSource.cs
@@ -0,0 +1,113 @@
+using System.Collections.Generic;
+using System.Collections.Specialized;
+using System.ComponentModel;
+using System.Linq;
+using System.Runtime.CompilerServices;
+using System.Threading.Tasks;
+
+namespace Xamarin.Forms.Pages
+{
+	public abstract class BaseDataSource : IDataSource, INotifyPropertyChanged
+	{
+		readonly DataSourceList _dataSourceList = new DataSourceList();
+		bool _initialized;
+		bool _isLoading;
+
+		public IReadOnlyList<IDataItem> Data
+		{
+			get
+			{
+				Initialize();
+				return _dataSourceList;
+			}
+		}
+
+		public bool IsLoading
+		{
+			get { return _isLoading; }
+			set
+			{
+				if (_isLoading == value)
+					return;
+				_isLoading = value;
+				OnPropertyChanged();
+			}
+		}
+
+#pragma warning disable CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+		public object this[string key]
+		{
+			get
+			{
+				Initialize();
+				return GetValue(key);
+			}
+			set
+			{
+				Initialize();
+				if (SetValue(key, value))
+					OnKeyChanged(key);
+			}
+		}
+#pragma warning restore CS4014 // Because this call is not awaited, execution of the current method continues before the call is completed
+
+		IEnumerable<string> IDataSource.MaskedKeys => _dataSourceList.MaskedKeys;
+
+		async void IDataSource.MaskKey(string key)
+		{
+			await Initialize();
+			_dataSourceList.MaskKey(key);
+		}
+
+		async void IDataSource.UnmaskKey(string key)
+		{
+			await Initialize();
+			_dataSourceList.UnmaskKey(key);
+		}
+
+		event PropertyChangedEventHandler INotifyPropertyChanged.PropertyChanged
+		{
+			add { PropertyChanged += value; }
+			remove { PropertyChanged -= value; }
+		}
+
+		protected abstract Task<IList<IDataItem>> GetRawData();
+
+		protected abstract object GetValue(string key);
+
+		protected void OnPropertyChanged([CallerMemberName] string property = null)
+		{
+			PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(property));
+		}
+
+		protected abstract bool SetValue(string key, object value);
+
+		async Task Initialize()
+		{
+			// Do this lazy because GetRawData is virtual and calling it in the ctor is therefor unfriendly
+			if (_initialized)
+				return;
+			_initialized = true;
+			IList<IDataItem> rawData = await GetRawData();
+			if (!(rawData is INotifyCollectionChanged))
+			{
+				Log.Warning("Xamarin.Forms.Pages", "DataSource does not implement INotifyCollectionChanged, updates will not be reflected");
+				rawData = rawData.ToList(); // Make a copy so we can be sure this list wont change out from under us
+			}
+			_dataSourceList.MainList = rawData;
+
+			// Test if INPC("Item") is enough to trigger a full reset rather than triggering a new event for each key?
+			foreach (IDataItem dataItem in rawData)
+			{
+				OnKeyChanged(dataItem.Name);
+			}
+		}
+
+		void OnKeyChanged(string key)
+		{
+			PropertyChanged?.Invoke(this, new PropertyChangedEventArgs($"Item[{key}]"));
+		}
+
+		event PropertyChangedEventHandler PropertyChanged;
+	}
+}
+\ No newline at end of file