[C#][iOS] Fix callbacks on AOT

Based on the idea of #386

csharp/Facebook.Yoga/Native.cs

@@ -58,6 +58,14 @@ namespace Facebook.Yoga
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
         public static extern int YGNodeGetInstanceCount();
 
+#if (UNITY_IOS && !UNITY_EDITOR) || __IOS__
+        [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
+        public static extern IntPtr YGNodeGetContext(IntPtr node);
+
+        [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
+        public static extern void YGNodeSetContext(YGNodeHandle node, IntPtr managed);
+#endif
+
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
         public static extern void YGSetExperimentalFeatureEnabled(
             YogaExperimentalFeature feature,
@@ -68,16 +76,20 @@ namespace Facebook.Yoga
             YogaExperimentalFeature feature);
 
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
-        public static extern void YGNodeInsertChild(YGNodeHandle node, YGNodeHandle child, uint index);
+        public static extern void YGNodeInsertChild(
+            YGNodeHandle node,
+            YGNodeHandle child,
+            uint index);
 
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
         public static extern void YGNodeRemoveChild(YGNodeHandle node, YGNodeHandle child);
 
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
-        public static extern void YGNodeCalculateLayout(YGNodeHandle node,
+        public static extern void YGNodeCalculateLayout(
-                            float availableWidth,
+            YGNodeHandle node,
-                            float availableHeight,
+            float availableWidth,
-                            YogaDirection parentDirection);
+            float availableHeight,
+            YogaDirection parentDirection);
 
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
         public static extern void YGNodeMarkDirty(YGNodeHandle node);
@@ -105,7 +117,9 @@ namespace Facebook.Yoga
             [MarshalAs(UnmanagedType.FunctionPtr)] YogaBaselineFunc baselineFunc);
 
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
-        public static extern void YGNodeSetHasNewLayout(YGNodeHandle node, [MarshalAs(UnmanagedType.I1)] bool hasNewLayout);
+        public static extern void YGNodeSetHasNewLayout(
+            YGNodeHandle node,
+            [MarshalAs(UnmanagedType.I1)] bool hasNewLayout);
 
         [DllImport(DllName, ExactSpelling = true, CallingConvention = CallingConvention.Cdecl)]
         [return: MarshalAs(UnmanagedType.I1)]

csharp/Facebook.Yoga/YogaLogger.cs

@@ -10,6 +10,10 @@
 using System;
 using System.Runtime.InteropServices;
 
+#if __IOS__
+using ObjCRuntime;
+#endif
+
 namespace Facebook.Yoga
 {
     internal static class YogaLogger
@@ -18,26 +22,30 @@ namespace Facebook.Yoga
         public delegate void Func(YogaLogLevel level, string message);
 
         private static bool _initialized;
-        private static Func _managedLogger = null;
 
         public static Func Logger = null;
 
+#if (UNITY_IOS && !UNITY_EDITOR) || __IOS__
+        [MonoPInvokeCallback(typeof(Func))]
+#endif
+        public static void LoggerInternal(YogaLogLevel level, string message)
+        {
+            if (Logger != null)
+            {
+                Logger(level, message);
+            }
+
+            if (level == YogaLogLevel.Error)
+            {
+                throw new InvalidOperationException(message);
+            }
+        }
+
         public static void Initialize()
         {
             if (!_initialized)
             {
-                _managedLogger = (level, message) => {
+                Native.YGInteropSetLogger(LoggerInternal);
-                    if (Logger != null)
-                    {
-                        Logger(level, message);
-                    }
-
-                    if (level == YogaLogLevel.Error)
-                    {
-                        throw new InvalidOperationException(message);
-                    }
-                };
-                Native.YGInteropSetLogger(_managedLogger);
                 _initialized = true;
             }
         }

csharp/Facebook.Yoga/YogaNode.cs

@@ -12,6 +12,11 @@ using System.Collections;
 using System.Collections.Generic;
 using System.Text;
 
+#if __IOS__
+using System.Runtime.InteropServices;
+using ObjCRuntime;
+#endif
+
 namespace Facebook.Yoga
 {
     public partial class YogaNode : IEnumerable<YogaNode>
@@ -20,10 +25,11 @@ namespace Facebook.Yoga
         private WeakReference _parent;
         private List<YogaNode> _children;
         private MeasureFunction _measureFunction;
-        private YogaMeasureFunc _ygMeasureFunc;
         private BaselineFunction _baselineFunction;
-        private YogaBaselineFunc _ygBaselineFunc;
         private object _data;
+#if (UNITY_IOS && !UNITY_EDITOR) || __IOS__
+        private GCHandle _managed;
+#endif
 
         public YogaNode()
         {
@@ -542,18 +548,58 @@ namespace Facebook.Yoga
             return _children != null ? _children.IndexOf(node) : -1;
         }
 
+#if (UNITY_IOS && !UNITY_EDITOR) || __IOS__
+        private void SetContext()
+        {
+            if (!_managed.IsAllocated)
+            {
+                _managed = GCHandle.Alloc(this, GCHandleType.Weak);
+                Native.YGNodeSetContext(_ygNode, GCHandle.ToIntPtr(_managed));
+            }
+        }
+
+        private static YogaNode GetManaged(IntPtr ygNodePtr)
+        {
+            var node = GCHandle.FromIntPtr(Native.YGNodeGetContext(ygNodePtr)).Target as YogaNode;
+            if (node == null)
+            {
+                throw new InvalidOperationException("YogaNode is already deallocated");
+            }
+
+            return node;
+        }
+#endif
+
         public void SetMeasureFunction(MeasureFunction measureFunction)
         {
             _measureFunction = measureFunction;
-            _ygMeasureFunc = measureFunction != null ? MeasureInternal : (YogaMeasureFunc)null;
+            YogaMeasureFunc func = null;
-            Native.YGNodeSetMeasureFunc(_ygNode, _ygMeasureFunc);
+            if (measureFunction != null)
+            {
+#if (UNITY_IOS && !UNITY_EDITOR) || __IOS__
+                SetContext();
+                func = MeasureInternalIOS;
+#else
+                func = MeasureInternal;
+#endif
+            }
+            Native.YGNodeSetMeasureFunc(_ygNode, func);
         }
 
         public void SetBaselineFunction(BaselineFunction baselineFunction)
         {
             _baselineFunction = baselineFunction;
-            _ygBaselineFunc = baselineFunction != null ? BaselineInternal : (YogaBaselineFunc)null;
+            YogaBaselineFunc func = null;
-            Native.YGNodeSetBaselineFunc(_ygNode, _ygBaselineFunc);
+            if (baselineFunction != null)
+            {
+#if (UNITY_IOS && !UNITY_EDITOR) || __IOS__
+                SetContext();
+                func = BaselineInternalIOS;
+#else
+                func = BaselineInternal;
+#endif
+            }
+            Native.YGNodeSetBaselineFunc(_ygNode, func);
         }
 
         public void CalculateLayout()
@@ -565,6 +611,20 @@ namespace Facebook.Yoga
                 Native.YGNodeStyleGetDirection(_ygNode));
         }
 
+#if (UNITY_IOS && !UNITY_EDITOR) || __IOS__
+        [MonoPInvokeCallback(typeof(YogaMeasureFunc))]
+        private static YogaSize MeasureInternalIOS(
+            IntPtr ygNodePtr,
+            float width,
+            YogaMeasureMode widthMode,
+            float height,
+            YogaMeasureMode heightMode)
+        {
+            var node = GetManaged(ygNodePtr);
+            return node.MeasureInternal(IntPtr.Zero, width, widthMode, height, heightMode);
+        }
+#endif
+
         private YogaSize MeasureInternal(
             IntPtr node,
             float width,
@@ -572,6 +632,7 @@ namespace Facebook.Yoga
             float height,
             YogaMeasureMode heightMode)
         {
+
             if (_measureFunction == null)
             {
                 throw new InvalidOperationException("Measure function is not defined.");
@@ -580,6 +641,18 @@ namespace Facebook.Yoga
             return _measureFunction(this, width, widthMode, height, heightMode);
         }
 
+#if (UNITY_IOS && !UNITY_EDITOR) || __IOS__
+        [MonoPInvokeCallback(typeof(YogaBaselineFunc))]
+        private static float BaselineInternalIOS(
+            IntPtr ygNodePtr,
+            float width,
+            float height)
+        {
+            var node = GetManaged(ygNodePtr);
+            return node.BaselineInternal(IntPtr.Zero, width, height);
+        }
+#endif
+
         private float BaselineInternal(IntPtr node, float width, float height)
         {
             if (_baselineFunction == null)