[restguide] fix indexing to prevent race condition

RestaurantGuide/iOS/AppDelegate.cs

@@ -35,11 +35,12 @@ public override bool FinishedLaunching (UIApplication app, NSDictionary options)
 
 			LoadApplication (new App ());
 
-			// for debugging Properties
+			// for debugging Application.Properties
 			var documents = Environment.GetFolderPath (Environment.SpecialFolder.MyDocuments); 
 			Console.WriteLine (documents);
 			// then look in /.config/.isolated-storage/PropertyStore.forms
 
+			// Index content for CoreSpotlight search!
 			if (UIDevice.CurrentDevice.CheckSystemVersion (9, 0)) {
 				// Code that requires iOS 9, like CoreSpotlight or 3D Touch
 				SearchModel = new SpotlightHelper (restaurants);

RestaurantGuide/iOS/SpotlightHelper.cs

@@ -8,6 +8,7 @@ namespace RestaurantGuide.iOS
 {
 	public class SpotlightHelper
 	{
+		/// <summary>Find a restaurant by a unique identifier</summary>
 		/// <returns>Restaurant Name</returns>
 		public string Lookup (string num) {
 			var res = from r in restaurants
@@ -20,13 +21,20 @@ public string Lookup (string num) {
 				return Random (); // HACK: deal with bad data from NSUserActivity (or CoreSpotlight)
 			}
 		}
+		/// <summary>
+		/// Select a random restaurant, used for the '
+		/// </summary>
 		public string Random () {
 			var r = new Random ();
 			var rn = r.Next (0, restaurants.Count - 1);
 			Console.WriteLine ($"Random number {rn} in {restaurants.Count}");
 			return restaurants[rn].Name;
 		}
 		List<Restaurant> restaurants;
+
+		/// <summary>
+		/// Add the restaurant collection to the CoreSpotlight index
+		/// </summary>
 		public SpotlightHelper (List<Restaurant> restaurants)
 		{
 			this.restaurants = restaurants;
@@ -35,30 +43,32 @@ public SpotlightHelper (List<Restaurant> restaurants)
 				var attributeSet = new CSSearchableItemAttributeSet (UTType.Text);
 				attributeSet.Title = r.Name;
 				attributeSet.ContentDescription = r.Cuisine;
-				attributeSet.TextContent = r.Chef;
+				attributeSet.TextContent = r.Chef; // also allow search by chef's name
 
 				var dataItem = new CSSearchableItem (r.Number.ToString(), "com.xamarin.restguide", attributeSet);
 				dataItems.Add (dataItem);
 			}
 
-			// HACK: index should be 'managed' rather than deleted/created each time - keep track of what's indexed?
+			// HACK: index could be 'managed' rather than deleted/created each time - keep track of what's indexed?
 			// see the "To9o" sample for a better user-input search indexing strategy
-			CSSearchableIndex.DefaultSearchableIndex.DeleteAll(null);
-
-			CSSearchableIndex.DefaultSearchableIndex.Index (dataItems.ToArray<CSSearchableItem> (), err => {
-				if (err != null) {
-					Console.WriteLine (err);
-					Xamarin.Insights.Report(new Exception("CoreSpotlight Index Failed"), new Dictionary <string, string> { 
-						{"Message", err.ToString()}
-					}, Xamarin.Insights.Severity.Error);
-				} else {
-					Console.WriteLine ("Indexed items successfully");
-					Xamarin.Insights.Track("CoreSpotlight", new Dictionary<string, string> {
-						{"Type", "Indexed successfully"}
-					});
-				}
+			CSSearchableIndex.DefaultSearchableIndex.DeleteAll(deletErr =>
+			{ 
+				// Start the new index only after the old one is completely deleted;
+				// important for larger indexes, where DeleteAll might take time to finish (thanks @jamesmontemagno)
+				CSSearchableIndex.DefaultSearchableIndex.Index (dataItems.ToArray<CSSearchableItem> (), err => {
+					if (err != null) {
+						Console.WriteLine ("Index failed " + err);
+						Xamarin.Insights.Report(new Exception("CoreSpotlight Index Failed"), new Dictionary <string, string> { 
+							{"Message", err.ToString()}
+						}, Xamarin.Insights.Severity.Error);
+					} else {
+						Console.WriteLine ("Indexed items successfully");
+						Xamarin.Insights.Track("CoreSpotlight", new Dictionary<string, string> {
+							{"Type", "Indexed successfully"}
+						});
+					}
+				});
 			});
 		}
 	}
-}
-
+}