fix up graph validation.

MaterialGraphProject/Assets/GraphFramework/SerializableGraph/Editor/Implementation/SerializableGraph.cs

             m_SerializableEdges = null;
             foreach (var edge in m_Edges)
                 AddEdgeToNodeEdges(edge);
-
-            OnEnable();
-            ValidateGraph();
         }
 
         public virtual void ValidateGraph()

MaterialGraphProject/Assets/GraphFramework/SerializableGraph/Editor/Implementation/SerializableGraphObject.cs

                 m_DeserializedGraph = deserializedGraph; // graph.ReplaceWith(m_DeserializedGraph);
         }
 
+        void Validate()
+        {
+
+            if (graph != null)
+            {
+                graph.OnEnable();
+                graph.ValidateGraph();
+            }
+        }
+
+            Validate();
+
             Undo.undoRedoPerformed += UndoRedoPerformed;
             UndoRedoPerformed();
         }

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/SubGraph/AbstractSubGraphNode.cs

                 }
 
                 var id = prop.guid.GetHashCode();
-                AddSlot(MaterialSlot.CreateMaterialSlot(slotType, id, prop.displayName, prop.referenceName, SlotType.Input, prop.defaultValue));
+                MaterialSlot slot = MaterialSlot.CreateMaterialSlot(slotType, id, prop.displayName, prop.referenceName, SlotType.Input, prop.defaultValue);
+                // copy default for texture for niceness
+                if (slotType == SlotValueType.Texture2D && propType == PropertyType.Texture)
+                {
+                    var tSlot = slot as Texture2DInputMaterialSlot;
+                    var tProp = prop as TextureShaderProperty;
+                    if (tSlot != null && tProp != null)
+                        tSlot.texture = tProp.value.texture;
+                }
+                AddSlot(slot);
                 validNames.Add(id);
             }
 

MaterialGraphProject/Assets/UnityShaderEditor/Editor/Data/SubGraph/SubGraphNode.cs

     [Title("Sub-graph/Sub-graph Node")]
     public class SubGraphNode : AbstractSubGraphNode
         , IGeneratesBodyCode
+        , IOnAssetEnabled
     {
         [SerializeField]
         private string m_SerializedSubGraph = string.Empty;
             outputString.AddShaderChunk("// Subgraph ends", false);
 
             shaderBodyVisitor.AddShaderChunk(outputString.GetShaderString(0), true);
+        }
+
+        public void OnEnable()
+        {
+            UpdateSlots();
         }
     }
 }