Overscroll and Elasticity for views::ScrollView

ui/views/examples/scroll_view_example.cc

Index: ui/views/examples/scroll_view_example.cc
diff --git a/ui/views/examples/scroll_view_example.cc b/ui/views/examples/scroll_view_example.cc
index 4fd1aaa2970948ed351eff7775a654532e9aa837..687056ce32bd3a5ce195c44cff60dd6fc62d6eca 100644
--- a/ui/views/examples/scroll_view_example.cc
+++ b/ui/views/examples/scroll_view_example.cc
@@ -64,11 +64,11 @@ void ScrollViewExample::CreateExampleView(View* container) {
   big_square_ = new LabelButton(this, ASCIIToUTF16("Big Square"));
   small_square_ = new LabelButton(this, ASCIIToUTF16("Small Square"));
   scroll_to_ = new LabelButton(this, ASCIIToUTF16("Scroll to"));
-  scrollable_ = new ScrollableView();
+  nested_ = new LabelButton(this, ASCIIToUTF16("Nested"));
   scroll_view_ = new ScrollView();
+  CreateScrollable();
   scroll_view_->SetContents(scrollable_);
-  scrollable_->SetBounds(0, 0, 1000, 100);
-  scrollable_->SetColor(SK_ColorYELLOW, SK_ColorCYAN);
+  nested_scrolls_ = nullptr;
 
   GridLayout* layout = new GridLayout(container);
   container->SetLayoutManager(layout);
@@ -82,7 +82,7 @@ void ScrollViewExample::CreateExampleView(View* container) {
 
   // Add control buttons.
   column_set = layout->AddColumnSet(1);
-  for (int i = 0; i < 5; i++) {
+  for (int i = 0; i < 6; i++) {
     column_set->AddColumn(GridLayout::FILL, GridLayout::FILL, 1,
                           GridLayout::USE_PREF, 0, 0);
   }
@@ -92,9 +92,50 @@ void ScrollViewExample::CreateExampleView(View* container) {
   layout->AddView(big_square_);
   layout->AddView(small_square_);
   layout->AddView(scroll_to_);
+  layout->AddView(nested_);
+}
+
+void ScrollViewExample::CreateScrollable() {
+  scrollable_ = new ScrollableView();
+  scrollable_->SetBounds(0, 0, 1000, 100);
+  scrollable_->SetColor(SK_ColorYELLOW, SK_ColorCYAN);
+}
+
+void ScrollViewExample::CreateNestedScrolls() {
+  const int kNestedHeight = 500;
+  nested_scrolls_ = new View();
+  nested_scrolls_->SetBounds(0, 0, 1000, kNestedHeight);
+  // Add two scroll views.
+  ScrollView* left = new ScrollView();
+  ScrollView* right = new ScrollView();
+  left->SetBounds(0, 0, 500, kNestedHeight);
+  right->SetBounds(500, 0, 500, kNestedHeight);
+
+  // The left scrollable is tall. Scrolling vertically inside it should scroll
+  // the inner ScrollView first, then the outer ScrollView when reaching the
+  // bounds. Scrolling horizontally should affect the outer scroll view, but
+  // elasticity should affect only the inner ScrollView (both directions).
+  CreateScrollable();
+  scrollable_->SetBounds(0, 0, 400, 1000);
+  left->SetContents(scrollable_);
+
+  // The right scrollable is too small to scroll. The outer scroll view should
+  // always scroll, and it should get all the elasticity.
+  CreateScrollable();
+  scrollable_->SetBounds(0, 0, 100, 100);
+  right->SetContents(scrollable_);
+
+  nested_scrolls_->AddChildView(left);
+  nested_scrolls_->AddChildView(right);
 }
 
 void ScrollViewExample::ButtonPressed(Button* sender, const ui::Event& event) {
+  if (nested_scrolls_ && sender != nested_) {
+    CreateScrollable();
+    scroll_view_->SetContents(scrollable_);
+    nested_scrolls_ = nullptr;
+  }
+
   if (sender == wide_) {
     scrollable_->SetBounds(0, 0, 1000, 100);
     scrollable_->SetColor(SK_ColorYELLOW, SK_ColorCYAN);
@@ -110,6 +151,10 @@ void ScrollViewExample::ButtonPressed(Button* sender, const ui::Event& event) {
   } else if (sender == scroll_to_) {
     scroll_view_->contents()->ScrollRectToVisible(
         gfx::Rect(20, 500, 1000, 500));
+  } else if (sender == nested_) {
+    if (!nested_scrolls_)
+      CreateNestedScrolls();
+    scroll_view_->SetContents(nested_scrolls_);
   }
   scroll_view_->Layout();
 }