Make Label display HTML from a string (#4527)

* Use UpdateText

* Added missing helper method and UI test

* Added missing helper for UWP

* Added csproj entry for helper

* Resolved rebase conflicts

* Update LabelRenderer.cs

* Update LabelRenderer.cs

* Update LabelRenderer.cs

* iOS Merge error fix

* Feedback

* - uwp fixes

* - android fix empty text

* - ios fix null and setting text when texttype starts as html

* - set _perfectSizeValid = false; after changed AttributedText

Setting the AttributedText causes GetDesiredSize to get called which sets _perfectSizeValid to true but at this point this frame still hasn't adjusted to any size change from *LayoutSubViews*. This resets _perfectSizeValid so after the AttributedText set the desiredsize can get pulled again

* Renamed PlainText to Text

* Fixed initial no HTML styling

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/LabelTextType.cs

@@ -0,0 +1,88 @@
+using System;
+using Xamarin.Forms.CustomAttributes;
+using Xamarin.Forms.Internals;
+
+#if UITEST
+using Xamarin.Forms.Core.UITests;
+using Xamarin.UITest;
+using NUnit.Framework;
+using System.Linq;
+#endif
+
+namespace Xamarin.Forms.Controls.Issues
+{
+#if UITEST
+	[Category(UITestCategories.Label)]
+#endif
+	[Preserve(AllMembers = true)]
+	[Issue(IssueTracker.None, 0, "Implementation of Label TextType", PlatformAffected.All)]
+	public class LabelTextType : TestContentPage
+	{
+		protected override void Init()
+		{
+			var label = new Label
+			{
+				AutomationId = "TextTypeLabel",
+				Text = "<h1>Hello World!</h1>"
+			};
+
+			var button = new Button
+			{
+				AutomationId = "ToggleTextTypeButton",
+				Text = "Toggle HTML/Plain"
+			};
+
+			button.Clicked += (s, a) =>
+			{
+				label.TextType = label.TextType == TextType.Html ? TextType.Text : TextType.Html;
+			};
+
+
+			Label htmlLabel = new Label() { TextType = TextType.Html };
+			Label normalLabel = new Label();
+			Label nullLabel = new Label() { TextType = TextType.Html };
+
+			Button toggle = new Button()
+			{
+				Text = "Toggle some more things",
+				Command = new Command(() =>
+				{
+					htmlLabel.Text = $"<b>{DateTime.UtcNow}</b>";
+					normalLabel.Text = $"<b>{DateTime.UtcNow}</b>";
+
+					if (String.IsNullOrWhiteSpace(nullLabel.Text))
+						nullLabel.Text = "hi there";
+					else
+						nullLabel.Text = null;
+				})
+			};
+
+
+			var stacklayout = new StackLayout();
+			stacklayout.Children.Add(label);
+			stacklayout.Children.Add(button);
+			stacklayout.Children.Add(htmlLabel);
+			stacklayout.Children.Add(normalLabel);
+			stacklayout.Children.Add(nullLabel);
+			stacklayout.Children.Add(toggle);
+
+			Content = stacklayout;
+		}
+
+#if UITEST
+		[Test]
+		public void LabelToggleHtmlAndPlainTextTest() 
+		{
+			RunningApp.WaitForElement ("TextTypeLabel");
+			RunningApp.Screenshot ("I see plain text");
+
+			Assert.IsTrue(RunningApp.Query("TextTypeLabel").FirstOrDefault()?.Text == "<h1>Hello World!</h1>");
+
+			RunningApp.Tap("ToggleTextTypeButton");
+			RunningApp.Screenshot ("I see HTML text");
+
+			Assert.IsFalse(RunningApp.Query("TextTypeLabel").FirstOrDefault()?.Text.Contains("<h1>") ?? true);
+		}
+#endif
+	}
+}

Xamarin.Forms.Controls.Issues/Xamarin.Forms.Controls.Issues.Shared/Xamarin.Forms.Controls.Issues.Shared.projitems

@@ -1029,6 +1029,7 @@
     <Compile Include="$(MSBuildThisFileDirectory)Issue6738.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)GitHub6926.cs" />
     <Compile Include="$(MSBuildThisFileDirectory)Issue5503.cs" />
+    <Compile Include="$(MSBuildThisFileDirectory)LabelTextType.cs" />
   </ItemGroup>
   <ItemGroup>
     <EmbeddedResource Include="$(MSBuildThisFileDirectory)Bugzilla22229.xaml">

Xamarin.Forms.Controls/CoreGalleryPages/LabelCoreGalleryPage.cs

@@ -236,6 +236,40 @@ protected override void Build (StackLayout stackLayout)
 					Padding = new Thickness(40, 20)
 				}
 			);
+
+			var htmlLabelContainer = new ViewContainer<Label>(Test.Label.TextType,
+				new Label
+				{
+					Text = "<h1>Hello world!</h1>",
+					TextType = TextType.Html
+				});
+
+			var htmlLabelMultipleLinesContainer = new ViewContainer<Label>(Test.Label.TextType,
+				new Label
+				{
+					Text = "<h1>Hello world!</h1><p>Lorem <strong>ipsum</strong> bla di bla <i>blabla</i> blablabl&nbsp;ablabla & blablablablabl ablabl ablablabl ablablabla blablablablablablab lablablabla blablab lablablabla blablabl ablablablab lablabla blab lablablabla blablab lablabla blablablablab lablabla blablab lablablabl ablablabla blablablablablabla blablabla</p>",
+					TextType = TextType.Html,
+					MaxLines = 3
+				});
+
+			var toggleLabel = new Label
+			{
+				TextType = TextType.Html,
+				Text = "<h1 style=\"color: red;\">Hello world!</h1><p>Lorem <strong>ipsum</strong></p>"
+
+			};
+
+			var gestureRecognizer = new TapGestureRecognizer();
+
+			gestureRecognizer.Tapped += (s, a) =>
+			{
+				toggleLabel.TextType = toggleLabel.TextType == TextType.Html ? TextType.Text : TextType.Html;
+			};
+
+			toggleLabel.GestureRecognizers.Add(gestureRecognizer);
+
+			var toggleHtmlPlainTextLabelContainer = new ViewContainer<Label>(Test.Label.TextType,
+				toggleLabel);
 
 			Add (namedSizeMediumBoldContainer);
 			Add (namedSizeMediumItalicContainer);
@@ -272,6 +306,9 @@ protected override void Build (StackLayout stackLayout)
 			Add (maxlinesTailTruncContainer);
 			Add (maxlinesWordWrapContainer);
 			Add(paddingContainer);
+			Add (htmlLabelContainer);
+			Add (htmlLabelMultipleLinesContainer);
+			Add (toggleHtmlPlainTextLabelContainer);
 		}
 	}
 }

Xamarin.Forms.Core/Label.cs

@@ -89,6 +89,9 @@ public class Label : View, IFontElement, ITextElement, ITextAlignmentElement, IL
 			});
 
 		public static readonly BindableProperty PaddingProperty = PaddingElement.PaddingProperty;
+
+		public static readonly BindableProperty TextTypeProperty = BindableProperty.Create(nameof(TextType), typeof(TextType), typeof(Label), TextType.Text,
+			propertyChanged: (bindable, oldvalue, newvalue) => ((Label)bindable).InvalidateMeasureInternal(InvalidationTrigger.MeasureChanged));
 
 		readonly Lazy<PlatformConfigurationRegistry<Label>> _platformConfigurationRegistry;
 
@@ -212,6 +215,12 @@ public Thickness Padding
 			get { return (Thickness)GetValue(PaddingProperty); }
 			set { SetValue(PaddingProperty, value); }
 		}
+
+		public TextType TextType
+		{
+			get => (TextType)GetValue(TextTypeProperty);
+			set => SetValue(TextTypeProperty, value);
+		}
 
 		double IFontElement.FontSizeDefaultValueCreator() =>
 			Device.GetNamedSize(NamedSize.Default, (Label)this);

Xamarin.Forms.Core/TextType.cs

@@ -0,0 +1,8 @@
+namespace Xamarin.Forms
+{
+	public enum TextType
+	{
+		Text,
+		Html
+	}
+}

Xamarin.Forms.CustomAttributes/TestAttributes.cs

@@ -635,7 +635,8 @@ public enum Label
 			VerticalTextAlignmentStart,
 			VerticalTextAlignmentCenter,
 			VerticalTextAlignmentEnd,
-			MaxLines
+			MaxLines,
+			TextType
 		}
 
 		public enum MasterDetailPage

Xamarin.Forms.Platform.Android/FastRenderers/LabelRenderer.cs

@@ -251,6 +251,7 @@ protected virtual void OnElementChanged(ElementChangedEventArgs<Label> e)
 					UpdateGravity();
 				if (e.OldElement?.MaxLines != e.NewElement.MaxLines)
 					UpdateMaxLines();
+
 				UpdatePadding();
 
 				ElevationHelper.SetElevation(this, e.NewElement);
@@ -263,7 +264,8 @@ protected virtual void OnElementPropertyChanged(object sender, PropertyChangedEv
 
 			if (e.PropertyName == Label.HorizontalTextAlignmentProperty.PropertyName || e.PropertyName == Label.VerticalTextAlignmentProperty.PropertyName)
 				UpdateGravity();
-			else if (e.PropertyName == Label.TextColorProperty.PropertyName)
+			else if (e.PropertyName == Label.TextColorProperty.PropertyName ||
+				e.PropertyName == Label.TextTypeProperty.PropertyName)
 				UpdateText();
 			else if (e.PropertyName == Label.FontProperty.PropertyName)
 				UpdateText();
@@ -380,7 +382,23 @@ void UpdateText()
 					SetTextColor(_labelTextColorDefault);
 					_lastUpdateColor = Color.Default;
 				}
-				Text = Element.Text;
+
+				switch (Element.TextType)
+				{
+					case TextType.Html:
+						if (Forms.IsNougatOrNewer)
+							Control.SetText(Html.FromHtml(Element.Text ?? string.Empty, FromHtmlOptions.ModeCompact), BufferType.Spannable);
+						else
+#pragma warning disable CS0618 // Type or member is obsolete
+							Control.SetText(Html.FromHtml(Element.Text ?? string.Empty), BufferType.Spannable);
+#pragma warning restore CS0618 // Type or member is obsolete
+						break;
+
+					default:
+						Text = Element.Text;
+						break;
+				}
+
 				UpdateColor();
 				UpdateFont();
 
@@ -416,4 +434,4 @@ void UpdatePadding()
 			_lastSizeRequest = null;
 		}
 	}
-}
+}

Xamarin.Forms.Platform.Android/Forms.cs

@@ -56,6 +56,7 @@ public static class Forms
 		static BuildVersionCodes? s_sdkInt;
 		static bool? s_isLollipopOrNewer;
 		static bool? s_isMarshmallowOrNewer;
+		static bool? s_isNougatOrNewer;
 
 		[Obsolete("Context is obsolete as of version 2.5. Please use a local context instead.")]
 		[EditorBrowsable(EditorBrowsableState.Never)]
@@ -98,6 +99,16 @@ internal static bool IsMarshmallowOrNewer
 			}
 		}
 
+		internal static bool IsNougatOrNewer
+		{
+			get
+			{
+				if (!s_isNougatOrNewer.HasValue)
+					s_isNougatOrNewer = (int)Build.VERSION.SdkInt >= 24;
+				return s_isNougatOrNewer.Value;
+			}
+		}
+
 		public static float GetFontSizeNormal(Context context)
 		{
 			float size = 50;

Xamarin.Forms.Platform.Android/Renderers/LabelRenderer.cs

@@ -135,7 +135,6 @@ protected override void OnElementChanged(ElementChangedEventArgs<Label> e)
 					UpdateMaxLines();
 				if (e.OldElement.CharacterSpacing != e.NewElement.CharacterSpacing)
 					UpdateCharacterSpacing();
-
 			}
 			UpdateTextDecorations();
 			UpdatePadding();
@@ -158,13 +157,13 @@ protected override void OnElementPropertyChanged(object sender, PropertyChangedE
 				UpdateLineBreakMode();
 			else if (e.PropertyName == Label.TextDecorationsProperty.PropertyName)
 				UpdateTextDecorations();
-			else if (e.PropertyName == Label.TextProperty.PropertyName || e.PropertyName == Label.FormattedTextProperty.PropertyName)
+			else if (e.IsOneOf(Label.TextProperty, Label.FormattedTextProperty, Label.TextTypeProperty))
 				UpdateText();
 			else if (e.PropertyName == Label.LineHeightProperty.PropertyName)
 				UpdateLineHeight();
 			else if (e.PropertyName == Label.MaxLinesProperty.PropertyName)
 				UpdateMaxLines();
-			else if (e.PropertyName == ImageButton.PaddingProperty.PropertyName)
+			else if (e.PropertyName == Label.PaddingProperty.PropertyName)
 				UpdatePadding();
 		}
 
@@ -242,7 +241,6 @@ void UpdateCharacterSpacing()
 			}
 		}
 
-
 		void UpdateLineHeight()
 		{
 			_lastSizeRequest = null;
@@ -274,7 +272,25 @@ void UpdateText()
 					_view.SetTextColor(_labelTextColorDefault);
 					_lastUpdateColor = Color.Default;
 				}
-				_view.Text = Element.Text;
+
+				switch (Element.TextType)
+				{
+
+					case TextType.Html:
+						if (Forms.IsNougatOrNewer)
+							Control.SetText(Html.FromHtml(Element.Text ?? string.Empty, FromHtmlOptions.ModeCompact), TextView.BufferType.Spannable);
+						else
+#pragma warning disable CS0618 // Type or member is obsolete
+							Control.SetText(Html.FromHtml(Element.Text ?? string.Empty), TextView.BufferType.Spannable);
+#pragma warning restore CS0618 // Type or member is obsolete
+						break;
+
+					default:
+						_view.Text = Element.Text;
+
+						break;
+				}
+
 				UpdateColor();
 				UpdateFont();