Merge pull request #36 from Redth/global-header-footer-hide-when-empty

Hide Global/Header Footer when adapter is empty

Sample/VirtualListViewSample/MusicLibraryPage.xaml

@@ -72,6 +72,15 @@
 				<Label Padding="20" Text="That's all folks!" TextColor="White" HorizontalOptions="Center" />
 			</Grid>
 		</vlv:VirtualListView.GlobalFooter>
+
+		<vlv:VirtualListView.EmptyView>
+			<Grid>
+				<Label
+					VerticalOptions="Center"
+					HorizontalOptions="Center"
+					Text="No Items" />
+			</Grid>
+		</vlv:VirtualListView.EmptyView>
 	</vlv:VirtualListView>
 
 </ContentPage>

VirtualListView/Adapters/VirtualListViewAdapterBase.cs

@@ -2,7 +2,12 @@
 
 public abstract class VirtualListViewAdapterBase<TSection, TItem> : IVirtualListViewAdapter
 {
-	public virtual int GetNumberOfSections() => 1;
+	// This adapter assumes we only ever have 1 section
+	// however we really want to return 0 if there's no items at all
+	// So, ask the derived class how many items might be in the first
+	// section and if any, we return 1 section otherwise 0
+	public virtual int GetNumberOfSections() =>
+		GetNumberOfItemsInSection(0) > 0 ? 1 : 0;
 
 	public event EventHandler OnDataInvalidated;
 

VirtualListView/PositionalViewSelector.cs

@@ -28,12 +28,32 @@ int GetTotalCount()
 	{
 		var sum = 0;
 
-		if (HasGlobalHeader)
-			sum += 1;
+		var hasAtLeastOneItem = false;
+		var numberOfSections = Adapter.GetNumberOfSections();
+
+		if (HasGlobalHeader && numberOfSections > 0)
+		{
+			// Make sure that there's at least one section with at least
+			// one item, otherwise it's 'empty'
+			// The default adapter may always return 1 for number of sections
+			// so it's not enough to check that
+			for (int s = 0; s < numberOfSections; s++)
+			{
+				if (Adapter.GetNumberOfItemsInSection(s) > 0)
+				{
+					sum += 1;
+					// If we found one, we can stop looping
+					// since we just care to calculate a spot
+					// for the header cell if the adapter isn't empty
+					hasAtLeastOneItem = true;
+					break;
+				}
+			}
+		}
 
 		if (Adapter != null)
 		{
-			for (int s = 0; s < Adapter.GetNumberOfSections(); s++)
+			for (int s = 0; s < numberOfSections; s++)
 			{
 				if (ViewSelector.SectionHasHeader(s))
 					sum += 1;
@@ -45,7 +65,9 @@ int GetTotalCount()
 			}
 		}
 
-		if (HasGlobalFooter)
+		// Only count footer if there is already at least one item
+		// otherwise the adapter is empty and we shouldn't count it
+		if (HasGlobalFooter && hasAtLeastOneItem)
 			sum += 1;
 
 		return sum;