[escher] Add a ScrollViewDelegate

escher/include/escher/scroll_view_data_source.h

@@ -3,12 +3,23 @@
 
 #include <kandinsky.h>
 
+class ScrollViewDataSource;
+
+class ScrollViewDelegate {
+public:
+  virtual void scrollViewDidChangeOffset(ScrollViewDataSource * scrollViewDataSource) = 0;
+};
+
 class ScrollViewDataSource {
 public:
-  ScrollViewDataSource();
-  KDPoint offset() const;
+  ScrollViewDataSource() : m_delegate(nullptr), m_offset(KDPointZero) {}
+  KDPoint offset() const { return m_offset; }
   bool setOffset(KDPoint offset);
+  void setScrollViewDelegate(ScrollViewDelegate * delegate) {
+    m_delegate = delegate;
+  }
 private:
+  ScrollViewDelegate * m_delegate;
   KDPoint m_offset;
 };
 

escher/include/escher/scrollable_view.h

@@ -6,7 +6,7 @@
 
 class ScrollableView : public Responder, public ScrollView {
 public:
- ScrollableView(Responder * parentResponder, View * view, ScrollViewDataSource * dataSource);
+  ScrollableView(Responder * parentResponder, View * view, ScrollViewDataSource * dataSource);
   bool handleEvent(Ion::Events::Event event) override;
   void reloadScroll(bool forceRelayout = false);
 protected:

escher/src/scroll_view_data_source.cpp

@@ -1,19 +1,12 @@
 #include <escher/scroll_view_data_source.h>
 
-ScrollViewDataSource::ScrollViewDataSource() :
-  m_offset(KDPointZero)
-{
-}
-
-KDPoint ScrollViewDataSource::offset() const {
-  return m_offset;
-}
-
 bool ScrollViewDataSource::setOffset(KDPoint offset) {
   if (offset != m_offset) {
     m_offset = offset;
+    if (m_delegate) {
+      m_delegate->scrollViewDidChangeOffset(this);
+    }
     return true;
   }
   return false;
 }
-