[csharp] Implement static methods for callbacks so they work on aot on iOS, use YogaRef to store pointer to managed YogaNode

csharp/Facebook.Yoga/Native.cs

@@ -111,6 +111,13 @@ namespace Facebook.Yoga
         [return: MarshalAs(UnmanagedType.I1)]
         public static extern bool YGNodeGetHasNewLayout(YGNodeHandle node);
 
+        [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
+        public static extern void YGNodeSetContext(YGNodeHandle node, IntPtr context);
+
+        [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
+        public static extern IntPtr YGNodeGetContext(IntPtr node);
+
+
         #endregion
 
         #region YG_NODE_STYLE_PROPERTY

csharp/Facebook.Yoga/YogaLogger.cs

@@ -37,9 +37,31 @@ namespace Facebook.Yoga
                         throw new InvalidOperationException(message);
                     }
                 };
+#if __IOS__
+                Native.YGInteropSetLogger(ManagedLogger);
+#else
                 Native.YGInteropSetLogger(_managedLogger);
+#endif
                 _initialized = true;
             }
         }
+
+#if __IOS__
+		delegate void ManagedLoggerCallback(YogaLogLevel level, string message);
+
+		[ObjCRuntime.MonoPInvokeCallback(typeof(ManagedLoggerCallback))]
+		public static void ManagedLogger(YogaLogLevel level, string message)
+		{
+			if (Logger != null)
+			{
+				Logger(level, message);
+			}
+
+			if (level == YogaLogLevel.Error)
+			{
+				throw new InvalidOperationException(message);
+			}
+		}
+#endif
     }
 }

csharp/Facebook.Yoga/YogaNode.cs

@@ -10,6 +10,7 @@
 using System;
 using System.Collections;
 using System.Collections.Generic;
+using System.Runtime.InteropServices;
 using System.Text;
 
 namespace Facebook.Yoga
@@ -546,6 +547,10 @@ namespace Facebook.Yoga
         {
             _measureFunction = measureFunction;
             _ygMeasureFunc = measureFunction != null ? MeasureInternal : (YogaMeasureFunc)null;
+
+            var handle = GCHandle.Alloc(this);
+            Native.YGNodeSetContext(_ygNode, GCHandle.ToIntPtr(handle));
+
             Native.YGNodeSetMeasureFunc(_ygNode, _ygMeasureFunc);
         }
 
@@ -553,6 +558,10 @@ namespace Facebook.Yoga
         {
             _baselineFunction = baselineFunction;
             _ygBaselineFunc = baselineFunction != null ? BaselineInternal : (YogaBaselineFunc)null;
+
+            var handle = GCHandle.Alloc(this);
+            Native.YGNodeSetContext(_ygNode, GCHandle.ToIntPtr(handle));
+
             Native.YGNodeSetBaselineFunc(_ygNode, _ygBaselineFunc);
         }
 
@@ -565,29 +574,47 @@ namespace Facebook.Yoga
                 Native.YGNodeStyleGetDirection(_ygNode));
         }
 
-        private YogaSize MeasureInternal(
+#if __IOS__
+        [ObjCRuntime.MonoPInvokeCallback(typeof(YogaMeasureFunc))]
+#endif
+        private static YogaSize MeasureInternal(
             IntPtr node,
             float width,
             YogaMeasureMode widthMode,
             float height,
             YogaMeasureMode heightMode)
         {
-            if (_measureFunction == null)
+
+            var yogaNodePointer = Native.YGNodeGetContext(node);
+
+            YogaNode yogaNode = GCHandle.FromIntPtr(yogaNodePointer).Target as YogaNode;
+
+            var measureFunction = yogaNode._measureFunction;
+            if (measureFunction == null)
             {
                 throw new InvalidOperationException("Measure function is not defined.");
             }
 
-            return _measureFunction(this, width, widthMode, height, heightMode);
+            return measureFunction(yogaNode, width, widthMode, height, heightMode);
         }
 
-        private float BaselineInternal(IntPtr node, float width, float height)
+
+#if __IOS__
+        [ObjCRuntime.MonoPInvokeCallback(typeof(YogaBaselineFunc))]
+#endif
+        private static float BaselineInternal(IntPtr node, float width, float height)
         {
-            if (_baselineFunction == null)
+            var yogaNodePointer = Native.YGNodeGetContext(node);
+
+            YogaNode yogaNode = GCHandle.FromIntPtr(yogaNodePointer).Target as YogaNode;
+
+            var baselineFunction = yogaNode._baselineFunction;
+            if (baselineFunction == null)
             {
                 throw new InvalidOperationException("Baseline function is not defined.");
             }
 
-            return _baselineFunction(this, width, height);
+            return baselineFunction(yogaNode, width, height);
         }
 
         public string Print(YogaPrintOptions options =