[All] Bindable span (xamarin#1850)

* Bindable Text Property on Span

* Style applied to Span

* Added style property

* Unit tests added

* Minor fix and cleanup

* Cleanup of code after review

* Updated docs

* Set Parent and reduce calls to Text property

* OneTime Binding

* Allow OneTime Binding as a default

* Updated docs

Xamarin.Forms.Controls/CoreGalleryPages/LabelCoreGalleryPage.cs

@@ -43,9 +43,9 @@ protected override void Build (StackLayout stackLayout)
 #pragma warning restore 618
 
 			var formattedString = new FormattedString ();
-			formattedString.Spans.Add (new Span { BackgroundColor = Color.Red, ForegroundColor = Color.Olive, Text = "Span 1 " });
-			formattedString.Spans.Add (new Span { BackgroundColor = Color.Black, ForegroundColor = Color.White, Text = "Span 2 " });
-			formattedString.Spans.Add (new Span { BackgroundColor = Color.Pink, ForegroundColor = Color.Purple, Text = "Span 3" });
+			formattedString.Spans.Add (new Span { BackgroundColor = Color.Red, TextColor = Color.Olive, Text = "Span 1 " });
+			formattedString.Spans.Add (new Span { BackgroundColor = Color.Black, TextColor = Color.White, Text = "Span 2 " });
+			formattedString.Spans.Add (new Span { BackgroundColor = Color.Pink, TextColor = Color.Purple, Text = "Span 3" });
 
 			var formattedTextContainer = new ViewContainer<Label> (Test.Label.FormattedText, new Label { FormattedText = formattedString });
 

Xamarin.Forms.Controls/GalleryPages/LabelGallery.cs

@@ -37,10 +37,10 @@ public LabelGallery ()
 			var formatted = new Label { FormattedText = new FormattedString { 
 					Spans = { 
 #pragma warning disable 618
-						new Span {Text="FormattedStrings ", ForegroundColor=Color.Blue, BackgroundColor = Color.Yellow, Font = Font.BoldSystemFontOfSize (NamedSize.Large)},
+						new Span {Text="FormattedStrings ", TextColor=Color.Blue, BackgroundColor = Color.Yellow, Font = Font.BoldSystemFontOfSize (NamedSize.Large)},
 #pragma warning restore 618
-						new Span {Text="are ", ForegroundColor=Color.Red, BackgroundColor = Color.Gray},
-						new Span {Text="not pretty!", ForegroundColor = Color.Green,},
+						new Span {Text="are ", TextColor=Color.Red, BackgroundColor = Color.Gray},
+						new Span {Text="not pretty!", TextColor = Color.Green,},
 					}
 				} };
 			var missingfont = new Label { Text = "Missing font: use default" };

Xamarin.Forms.Core.UnitTests/SpanTests.cs

@@ -0,0 +1,86 @@
+using NUnit.Framework;
+
+namespace Xamarin.Forms.Core.UnitTests
+{
+	[TestFixture]
+	public class SpanTests : BaseTestFixture
+	{
+		[SetUp]
+		public override void Setup()
+		{
+			base.Setup();
+			Device.PlatformServices = new MockPlatformServices();
+		}
+
+		[TearDown]
+		public override void TearDown()
+		{
+			base.TearDown();
+			Device.PlatformServices = null;
+		}
+
+		[Test]
+		public void StyleApplied()
+		{
+			var pinkStyle = new Style(typeof(Span))
+			{
+				Setters = {
+					new Setter { Property = Span.TextColorProperty, Value = Color.Pink },
+				},
+				Class = "pink",
+				ApplyToDerivedTypes = true,
+			};
+
+			var span = new Span
+			{
+				Style = pinkStyle
+			};
+
+			var formattedText = new FormattedString();
+			formattedText.Spans.Add(span);
+
+			var label = new Label()
+			{
+				FormattedText = formattedText
+			};
+
+			new ContentView
+			{
+				Resources = new ResourceDictionary { pinkStyle },
+				Content = label
+			};
+
+			Assert.AreEqual(Color.Pink, span.TextColor);
+		}
+
+		[Test]
+		public void BindingApplied()
+		{
+			var vm = new ViewModel()
+			{
+				Text = "CheckBindingWorked"
+			};
+
+			var formattedText = new FormattedString();
+
+			var label = new Label()
+			{
+				FormattedText = formattedText
+			};
+
+			var span = new Span();
+			span.SetBinding(Span.TextProperty, "Text");
+
+			formattedText.Spans.Add(span);
+
+			label.BindingContext = vm;
+
+			Assert.AreEqual(vm.Text, span.Text);
+		}
+
+		class ViewModel
+		{
+			public string Text { get; set; }
+		}
+	}
+}

Xamarin.Forms.Core.UnitTests/Xamarin.Forms.Core.UnitTests.csproj

@@ -78,6 +78,7 @@
     <Compile Include="FlowDirectionTests.cs" />
     <Compile Include="LayoutChildIntoBoundingRegionTests.cs" />
     <Compile Include="MenuUnitTests.cs" />
+    <Compile Include="SpanTests.cs" />
     <Compile Include="TemplatedViewUnitTests.cs" />
     <Compile Include="TemplatedPageUnitTests.cs" />
     <Compile Include="ContentFormUnitTests.cs" />
@@ -226,5 +227,4 @@
       <LogicalName>Images/crimson.jpg</LogicalName>
     </EmbeddedResource>
   </ItemGroup>
-  <ItemGroup />
 </Project>

Xamarin.Forms.Core/BindableProperty.cs

@@ -66,7 +66,7 @@ public sealed class BindableProperty
 				throw new ArgumentNullException("declaringType");
 
 			// don't use Enum.IsDefined as its redonkulously expensive for what it does
-			if (defaultBindingMode != BindingMode.Default && defaultBindingMode != BindingMode.OneWay && defaultBindingMode != BindingMode.OneWayToSource && defaultBindingMode != BindingMode.TwoWay)
+			if (defaultBindingMode != BindingMode.Default && defaultBindingMode != BindingMode.OneWay && defaultBindingMode != BindingMode.OneWayToSource && defaultBindingMode != BindingMode.TwoWay && defaultBindingMode != BindingMode.OneTime)
 				throw new ArgumentException("Not a valid type of BindingMode", "defaultBindingMode");
 			if (defaultValue == null && Nullable.GetUnderlyingType(returnType) == null && returnType.GetTypeInfo().IsValueType)
 				throw new ArgumentException("Not a valid default value", "defaultValue");

Xamarin.Forms.Core/FormattedString.cs

@@ -4,12 +4,11 @@
 using System.Collections.Specialized;
 using System.ComponentModel;
 using System.Linq;
-using System.Runtime.CompilerServices;
 
 namespace Xamarin.Forms
 {
 	[ContentProperty("Spans")]
-	public class FormattedString : INotifyPropertyChanged
+	public class FormattedString : Element
 	{
 		readonly SpanCollection _spans = new SpanCollection();
 
@@ -18,13 +17,18 @@ public FormattedString()
 			_spans.CollectionChanged += OnCollectionChanged;
 		}
 
+		protected override void OnBindingContextChanged()
+		{
+			base.OnBindingContextChanged();
+			for (int i = 0; i < Spans.Count; i++)
+				SetInheritedBindingContext(Spans[i], BindingContext);			
+		}
+
 		public IList<Span> Spans
 		{
 			get { return _spans; }
 		}
-
-		public event PropertyChangedEventHandler PropertyChanged;
-
+
 		public static explicit operator string(FormattedString formatted)
 		{
 			return formatted.ToString();
@@ -47,6 +51,7 @@ void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
 				foreach (object item in e.OldItems)
 				{
 					var bo = item as Span;
+					bo.Parent = null;
 					if (bo != null)
 						bo.PropertyChanged -= OnItemPropertyChanged;
 				}
@@ -57,6 +62,7 @@ void OnCollectionChanged(object sender, NotifyCollectionChangedEventArgs e)
 				foreach (object item in e.NewItems)
 				{
 					var bo = item as Span;
+					bo.Parent = this;
 					if (bo != null)
 						bo.PropertyChanged += OnItemPropertyChanged;
 				}
@@ -70,9 +76,6 @@ void OnItemPropertyChanged(object sender, PropertyChangedEventArgs e)
 			OnPropertyChanged("Spans");
 		}
 
-		void OnPropertyChanged([CallerMemberName] string propertyName = null)
-			=> PropertyChanged?.Invoke(this, new PropertyChangedEventArgs(propertyName));
-
 		class SpanCollection : ObservableCollection<Span>
 		{
 			protected override void InsertItem(int index, Span item)

Xamarin.Forms.Core/Label.cs

@@ -24,29 +24,38 @@ public class Label : View, IFontElement, ITextElement, ITextAlignmentElement, IE
 
 		public static readonly BindableProperty FontProperty = FontElement.FontProperty;
 
-		public static readonly BindableProperty TextProperty = BindableProperty.Create("Text", typeof(string), typeof(Label), default(string), propertyChanged: OnTextPropertyChanged);
+		public static readonly BindableProperty TextProperty = BindableProperty.Create(nameof(Text), typeof(string), typeof(Label), default(string), propertyChanged: OnTextPropertyChanged);
 
 		public static readonly BindableProperty FontFamilyProperty = FontElement.FontFamilyProperty;
 
 		public static readonly BindableProperty FontSizeProperty = FontElement.FontSizeProperty;
 
 		public static readonly BindableProperty FontAttributesProperty = FontElement.FontAttributesProperty;
 
-		public static readonly BindableProperty FormattedTextProperty = BindableProperty.Create("FormattedText", typeof(FormattedString), typeof(Label), default(FormattedString),
+		public static readonly BindableProperty FormattedTextProperty = BindableProperty.Create(nameof(FormattedText), typeof(FormattedString), typeof(Label), default(FormattedString),
 			propertyChanging: (bindable, oldvalue, newvalue) =>
 			{
 				if (oldvalue != null)
-					((FormattedString)oldvalue).PropertyChanged -= ((Label)bindable).OnFormattedTextChanged;
+				{
+					var formattedString = ((FormattedString)oldvalue);
+					formattedString.PropertyChanged -= ((Label)bindable).OnFormattedTextChanged;
+					formattedString.Parent = null;
+				}
 			}, propertyChanged: (bindable, oldvalue, newvalue) =>
 			{
 				if (newvalue != null)
-					((FormattedString)newvalue).PropertyChanged += ((Label)bindable).OnFormattedTextChanged;
+				{
+					var formattedString = (FormattedString)newvalue;
+					formattedString.PropertyChanged += ((Label)bindable).OnFormattedTextChanged;
+					formattedString.Parent = (Label)bindable;
+				}
+
 				((Label)bindable).InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged);
 				if (newvalue != null)
 					((Label)bindable).Text = null;
 			});
 
-		public static readonly BindableProperty LineBreakModeProperty = BindableProperty.Create("LineBreakMode", typeof(LineBreakMode), typeof(Label), LineBreakMode.WordWrap,
+		public static readonly BindableProperty LineBreakModeProperty = BindableProperty.Create(nameof(LineBreakMode), typeof(LineBreakMode), typeof(Label), LineBreakMode.WordWrap,
 			propertyChanged: (bindable, oldvalue, newvalue) => ((Label)bindable).InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged));
 
 		readonly Lazy<PlatformConfigurationRegistry<Label>> _platformConfigurationRegistry;
@@ -56,6 +65,13 @@ public Label()
 			_platformConfigurationRegistry = new Lazy<PlatformConfigurationRegistry<Label>>(() => new PlatformConfigurationRegistry<Label>(this));
 		}
 
+		protected override void OnBindingContextChanged()
+		{
+			base.OnBindingContextChanged();
+			if (FormattedText != null)
+				SetInheritedBindingContext(FormattedText, this.BindingContext);
+		}
+
 		[Obsolete("Font is obsolete as of version 1.3.0. Please use the Font attributes which are on the class itself.")]
 		public Font Font
 		{