[Core] Share BP across IFontElement implementors (#783)

* [Core] Share BP accross IFontElement implementors

* make sure the converter is used

1 files changed, 32 insertions, 17 deletions

diff --git a/Xamarin.Forms.Core/Span.cs b/Xamarin.Forms.Core/Span.cs
index 6ffc3f17..a410c100 100644
--- a/Xamarin.Forms.Core/Span.cs
+++ b/Xamarin.Forms.Core/Span.cs
@@ -84,9 +84,11 @@ namespace Xamarin.Forms
 			{
 				if (_fontAttributes == value)
 					return;
+				var oldValue = _fontAttributes;
 				_fontAttributes = value;
 				OnPropertyChanged();
-				UpdateStructFromFontProperties();
+
+				((IFontElement)this).OnFontAttributesChanged(oldValue, value);
 			}
 		}
 
@@ -97,9 +99,10 @@ namespace Xamarin.Forms
 			{
 				if (_fontFamily == value)
 					return;
+				var oldValue = _fontFamily;
 				_fontFamily = value;
 				OnPropertyChanged();
-				UpdateStructFromFontProperties();
+				((IFontElement)this).OnFontFamilyChanged(oldValue, value);
 			}
 		}
 
@@ -111,9 +114,10 @@ namespace Xamarin.Forms
 			{
 				if (_fontSize == value)
 					return;
+				var oldValue = _fontSize;
 				_fontSize = value;
 				OnPropertyChanged();
-				UpdateStructFromFontProperties();
+				((IFontElement)this).OnFontSizeChanged(oldValue, value);
 			}
 		}
 
@@ -149,23 +153,34 @@ namespace Xamarin.Forms
 			_inUpdate = false;
 		}
 
-		void UpdateStructFromFontProperties()
+		void OnSomeFontPropertyChanged()
 		{
-			if (_inUpdate)
-				return;
-			_inUpdate = true;
-
-			if (FontFamily != null)
 			{
-				Font = Font.OfSize(FontFamily, FontSize).WithAttributes(FontAttributes);
-			}
-			else
-			{
-				Font = Font.SystemFontOfSize(FontSize).WithAttributes(FontAttributes);
-			}
+				if (_inUpdate)
+					return;
+				_inUpdate = true;
 
-			_inUpdate = false;
+				if (FontFamily != null)
+					Font = Font.OfSize(FontFamily, FontSize).WithAttributes(FontAttributes);
+				else
+					Font = Font.SystemFontOfSize(FontSize).WithAttributes(FontAttributes);
+
+				_inUpdate = false;
+			}
 		}
-	}
+
 #pragma warning restore
+
+		void IFontElement.OnFontFamilyChanged(string oldValue, string newValue) =>
+			OnSomeFontPropertyChanged();
+
+		void IFontElement.OnFontSizeChanged(double oldValue, double newValue) =>
+			OnSomeFontPropertyChanged();
+
+		double IFontElement.FontSizeDefaultValueCreator() =>
+			Device.GetNamedSize(NamedSize.Default, typeof(Label));
+
+		void IFontElement.OnFontAttributesChanged(FontAttributes oldValue, FontAttributes newValue) =>
+			OnSomeFontPropertyChanged();
+	}
 }
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