Initial import

1 files changed, 56 insertions, 0 deletions

diff --git a/Xamarin.Forms.Core/Constraint.cs b/Xamarin.Forms.Core/Constraint.cs
new file mode 100644
index 00000000..bd219f0a
--- /dev/null
+++ b/Xamarin.Forms.Core/Constraint.cs
@@ -0,0 +1,56 @@
+using System;
+using System.Collections.Generic;
+using System.Linq.Expressions;
+
+namespace Xamarin.Forms
+{
+	[TypeConverter(typeof(ConstraintTypeConverter))]
+	public sealed class Constraint
+	{
+		Func<RelativeLayout, double> _measureFunc;
+
+		Constraint()
+		{
+		}
+
+		internal IEnumerable<View> RelativeTo { get; set; }
+
+		public static Constraint Constant(double size)
+		{
+			var result = new Constraint { _measureFunc = parent => size };
+
+			return result;
+		}
+
+		public static Constraint FromExpression(Expression<Func<double>> expression)
+		{
+			Func<double> compiled = expression.Compile();
+			var result = new Constraint
+			{
+				_measureFunc = layout => compiled(),
+				RelativeTo = ExpressionSearch.Default.FindObjects<View>(expression).ToArray() // make sure we have our own copy
+			};
+
+			return result;
+		}
+
+		public static Constraint RelativeToParent(Func<RelativeLayout, double> measure)
+		{
+			var result = new Constraint { _measureFunc = measure };
+
+			return result;
+		}
+
+		public static Constraint RelativeToView(View view, Func<RelativeLayout, View, double> measure)
+		{
+			var result = new Constraint { _measureFunc = layout => measure(layout, view), RelativeTo = new[] { view } };
+
+			return result;
+		}
+
+		internal double Compute(RelativeLayout parent)
+		{
+			return _measureFunc(parent);
+		}
+	}
+}
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