Disable removal of a required node

Scripts/Editor/NodeEditor.cs

@@ -67,7 +67,7 @@ namespace XNodeEditor {
             serializedObject.ApplyModifiedProperties();
 
 #if ODIN_INSPECTOR
-            // Call repaint so that the graph window elements respond properly to layout changes coming from Odin    
+            // Call repaint so that the graph window elements respond properly to layout changes coming from Odin
             if (GUIHelper.RepaintRequested) {
                 GUIHelper.ClearRepaintRequest();
                 window.Repaint();
@@ -106,17 +106,22 @@ namespace XNodeEditor {
 
         /// <summary> Add items for the context menu when right-clicking this node. Override to add custom menu items. </summary>
         public virtual void AddContextMenuItems(GenericMenu menu) {
+            bool canRemove = true;
             // Actions if only one node is selected
             if (Selection.objects.Length == 1 && Selection.activeObject is XNode.Node) {
                 XNode.Node node = Selection.activeObject as XNode.Node;
                 menu.AddItem(new GUIContent("Move To Top"), false, () => NodeEditorWindow.current.MoveNodeToTop(node));
                 menu.AddItem(new GUIContent("Rename"), false, NodeEditorWindow.current.RenameSelectedNode);
+
+                canRemove = NodeGraphEditor.GetEditor(node.graph, NodeEditorWindow.current).CanRemove(node);
             }
 
             // Add actions to any number of selected nodes
             menu.AddItem(new GUIContent("Copy"), false, NodeEditorWindow.current.CopySelectedNodes);
             menu.AddItem(new GUIContent("Duplicate"), false, NodeEditorWindow.current.DuplicateSelectedNodes);
-            menu.AddItem(new GUIContent("Remove"), false, NodeEditorWindow.current.RemoveSelectedNodes);
+
+            if (canRemove) menu.AddItem(new GUIContent("Remove"), false, NodeEditorWindow.current.RemoveSelectedNodes);
+            else menu.AddItem(new GUIContent("Remove"), false, null);
 
             // Custom sctions if only one node is selected
             if (Selection.objects.Length == 1 && Selection.activeObject is XNode.Node) {
@@ -132,11 +137,10 @@ namespace XNodeEditor {
             OnRename();
             AssetDatabase.ImportAsset(AssetDatabase.GetAssetPath(target));
         }
-        
+
         /// <summary> Called after this node's name has changed. </summary>
         public virtual void OnRename() { }
-        
+
-        
         [AttributeUsage(AttributeTargets.Class)]
         public class CustomNodeEditorAttribute : Attribute,
         XNodeEditor.Internal.NodeEditorBase<NodeEditor, NodeEditor.CustomNodeEditorAttribute, XNode.Node>.INodeEditorAttrib {
@@ -152,4 +156,4 @@ namespace XNodeEditor {
             }
         }
     }
-}
+}

Scripts/Editor/NodeGraphEditor.cs

@@ -181,8 +181,25 @@ namespace XNodeEditor {
             return node;
         }
 
+        /// <summary> Return false for nodes that can't be removed </summary>
+        public virtual bool CanRemove(XNode.Node node) {
+            // Check graph attributes to see if this node is required
+            Type graphType = target.GetType();
+            XNode.NodeGraph.RequireNodeAttribute[] attribs = Array.ConvertAll(
+                graphType.GetCustomAttributes(typeof(XNode.NodeGraph.RequireNodeAttribute), true), x => x as XNode.NodeGraph.RequireNodeAttribute);
+            if (attribs.Any(x => x.Requires(node.GetType()))) {
+                if (target.nodes.Count(x => x.GetType() == node.GetType()) <= 1) {
+                    return false;
+                }
+            }
+            return true;
+        }
+
         /// <summary> Safely remove a node and all its connections. </summary>
         public virtual void RemoveNode(XNode.Node node) {
+            if (!CanRemove(node)) return;
+
+            // Remove the node
             Undo.RecordObject(node, "Delete Node");
             Undo.RecordObject(target, "Delete Node");
             foreach (var port in node.Ports)

Scripts/Editor/NodeGraphImporter.cs

@@ -23,20 +23,23 @@ namespace XNodeEditor {
                 NodeGraph.RequireNodeAttribute[] attribs = Array.ConvertAll(
                     graphType.GetCustomAttributes(typeof(NodeGraph.RequireNodeAttribute), true), x => x as NodeGraph.RequireNodeAttribute);
 
-
                 Vector2 position = Vector2.zero;
                 foreach (NodeGraph.RequireNodeAttribute attrib in attribs) {
-                    if (attrib.type0 != null) {
+                    if (attrib.type0 != null) AddRequired(graph, attrib.type0, ref position);
-                        if (!graph.nodes.Any(x => x.GetType() == attrib.type0)) {
+                    if (attrib.type1 != null) AddRequired(graph, attrib.type1, ref position);
-                            XNode.Node node = graph.AddNode(attrib.type0);
+                    if (attrib.type2 != null) AddRequired(graph, attrib.type2, ref position);
-                            node.position = position;
-                            position.x += 200;
-                            if (node.name == null || node.name.Trim() == "") node.name = NodeEditorUtilities.NodeDefaultName(attrib.type0);
-                            if (!string.IsNullOrEmpty(AssetDatabase.GetAssetPath(graph))) AssetDatabase.AddObjectToAsset(node, graph);
-                        }
-                    }
                 }
             }
         }
+
+        private static void AddRequired(NodeGraph graph, Type type, ref Vector2 position) {
+            if (!graph.nodes.Any(x => x.GetType() == type)) {
+                XNode.Node node = graph.AddNode(type);
+                node.position = position;
+                position.x += 200;
+                if (node.name == null || node.name.Trim() == "") node.name = NodeEditorUtilities.NodeDefaultName(type);
+                if (!string.IsNullOrEmpty(AssetDatabase.GetAssetPath(graph))) AssetDatabase.AddObjectToAsset(node, graph);
+            }
+        }
     }
 }

Scripts/NodeGraph.cs

@@ -110,6 +110,14 @@ namespace XNode {
                 this.type1 = type2;
                 this.type2 = type3;
             }
+
+            public bool Requires(Type type) {
+                if (type == null) return false;
+                if (type == type0) return true;
+                else if (type == type1) return true;
+                else if (type == type2) return true;
+                return false;
+            }
         }
 #endregion
     }