Add BLayoutItem::LayoutInvalidated() hook. Leave BLayoutItem::InvalidateLayout() (and therefore BLayout::InvalidateLayout()) virtual. This is needed to let BLayout override it for invalidation propagations.

headers/os/interface/Layout.h

@@ -48,7 +48,7 @@ public:
 
 	// Layouting related methods
 
-			void				InvalidateLayout(bool children = false);
+	virtual	void				InvalidateLayout(bool children = false);
 			void				Relayout(bool immediate = false);
 			void				RequireLayout();
 			bool				IsValid();

headers/os/interface/LayoutItem.h

@@ -59,10 +59,11 @@ public:
 	virtual	status_t			AllUnarchived(const BMessage* from);
 
 protected:
-
 			void				SetLayout(BLayout* layout);
 
 	// hook methods
+	virtual	void				LayoutInvalidated(bool children);
+
 	virtual	void				AttachedToLayout();
 	virtual	void				DetachedFromLayout(BLayout* layout);
 

src/kits/interface/LayoutItem.cpp

@@ -72,6 +72,7 @@ BLayoutItem::View()
 void
 BLayoutItem::InvalidateLayout(bool children)
 {
+	LayoutInvalidated(children);
 	if (fLayout)
 		fLayout->InvalidateLayout(children);
 }
@@ -183,6 +184,13 @@ BLayoutItem::SetLayout(BLayout* layout)
 }
 
 
+void
+BLayoutItem::LayoutInvalidated(bool children)
+{
+	// hook method
+}
+
+
 void
 BLayoutItem::AttachedToLayout()
 {

src/kits/interface/ViewLayoutItem.cpp

@@ -157,13 +157,6 @@ BViewLayoutItem::View()
 }
 
 
-void
-BViewLayoutItem::InvalidateLayout(bool children)
-{
-	fView->InvalidateLayout(children);
-}
-
-
 void
 BViewLayoutItem::Relayout(bool immediate)
 {
@@ -220,6 +213,13 @@ BViewLayoutItem::Instantiate(BMessage* from)
 }
 
 
+void
+BViewLayoutItem::LayoutInvalidated(bool children)
+{
+	fView->InvalidateLayout(children);
+}
+
+
 void
 BViewLayoutItem::AncestorVisibilityChanged(bool shown)
 {

src/kits/interface/ViewLayoutItem.h

@@ -36,7 +36,6 @@ public:
 
 	virtual	BView*				View();
 
-	virtual	void				InvalidateLayout(bool children = false);
 	virtual	void				Relayout(bool immediate = false);
 
 	virtual	status_t			Archive(BMessage* into, bool deep = true) const;
@@ -45,6 +44,7 @@ public:
 	static	BArchivable*		Instantiate(BMessage* from);
 
 protected:
+	virtual	void				LayoutInvalidated(bool children);
 	virtual void				AncestorVisibilityChanged(bool shown);
 
 private: