Possibility to disable Snaplines in a Derived Extension via returning CanPlace = false

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/Extensions/DefaultPlacementBehavior.cs

@@ -50,7 +50,7 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 			ExtendedItem.AddBehavior(typeof(IPlacementBehavior), this);
 		}
 
-		public virtual bool CanPlace(ICollection<DesignItem> childItems, PlacementType type, PlacementAlignment position)
+		public virtual bool CanPlace(IEnumerable<DesignItem> childItems, PlacementType type, PlacementAlignment position)
 		{
 			return true;
 		}
@@ -80,6 +80,11 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 		{
 		}
 
+		public virtual bool CanPlaceItem(PlacementInformation info)
+		{
+			return true;
+		}
+
 		public virtual void SetPosition(PlacementInformation info)
 		{
 			if (info.Operation.Type != PlacementType.Move)

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/Extensions/SnaplinePlacementBehavior.cs

@@ -225,6 +225,9 @@ namespace ICSharpCode.WpfDesign.Designer.Extensions
 			
 			AddLines(containerRect, 0, false);
 
+			if (!CanPlace(operation.PlacedItems.Select(x => x.Item), operation.Type, PlacementAlignment.Center))
+				return;
+
 			foreach (var item in AllDesignItems() /* ExtendedItem.ContentProperty.CollectionElements */
 			         .Except(operation.PlacedItems.Select(f => f.Item))
 			         .Where(x=> x.View != null && !GetDisableSnaplines(x.View))) {

src/AddIns/DisplayBindings/WpfDesign/WpfDesign.Designer/Project/RootItemBehavior.cs

@@ -38,12 +38,9 @@ namespace ICSharpCode.WpfDesign.Designer
 			_rootItem.AddBehavior(typeof(IRootPlacementBehavior),this);
 		}
 
-		public bool CanPlace(System.Collections.Generic.ICollection<DesignItem> childItems, PlacementType type, PlacementAlignment position)
+		public bool CanPlace(IEnumerable<DesignItem> childItems, PlacementType type, PlacementAlignment position)
 		{
-			return type == PlacementType.Resize &&
-				(position == PlacementAlignment.Right
-				 || position == PlacementAlignment.BottomRight
-				 || position == PlacementAlignment.Bottom);
+			return type == PlacementType.Resize && (position == PlacementAlignment.Right || position == PlacementAlignment.BottomRight || position == PlacementAlignment.Bottom);
 		}
 		
 		public void BeginPlacement(PlacementOperation operation)

src/AddIns/DisplayBindings/WpfDesign/WpfDesign/Project/PlacementBehavior.cs

@@ -31,7 +31,7 @@ namespace ICSharpCode.WpfDesign
 		/// <summary>
 		/// Gets if the child element can be resized.
 		/// </summary>
-		bool CanPlace(ICollection<DesignItem> childItems, PlacementType type, PlacementAlignment position);
+		bool CanPlace(IEnumerable<DesignItem> childItems, PlacementType type, PlacementAlignment position);
 		
 		/// <summary>
 		/// Starts placement mode for this container.