[ash-md] Makes Wi-Fi header row sticky when network list is scrolled

ash/common/system/tray/tray_details_view.cc

Index: ash/common/system/tray/tray_details_view.cc
diff --git a/ash/common/system/tray/tray_details_view.cc b/ash/common/system/tray/tray_details_view.cc
index c34c81bafa848cf0048dcb592ba386d6921b76bd..a0d694d490c64fb3d54594fe13dafa8b531ec709 100644
--- a/ash/common/system/tray/tray_details_view.cc
+++ b/ash/common/system/tray/tray_details_view.cc
@@ -15,7 +15,119 @@
 #include "ui/views/controls/scroll_view.h"
 #include "ui/views/layout/box_layout.h"
 
-namespace ash {
+namespace {
+
+const int kHeaderRowId = 1000;
+const int kHeaderRowSeparatorThickness = 1;
+const SkColor kHeaderRowSeparatorColor = SkColorSetA(SK_ColorBLACK, 0x1F);
+
+// A view that is used as ScrollView contents. It supports designating some of
+// the children as sticky header rows. The sticky header rows are not scrolled
+// above the top of the visible viewport and are painted above other children.
+// To indicate that a child is a sticky header row use set_id(kHeaderRowId).
+class ScrollContentsView : public views::View {
+ public:
+  ScrollContentsView(ash::TrayDetailsView* tray_details_view) {}
+  ~ScrollContentsView() override {}
+
+ protected:
+  // views::View.
+  void OnBoundsChanged(const gfx::Rect& previous_bounds) override {
+    ScrollChildren();
+  }
+
+  void PaintChildren(const ui::PaintContext& context) override {
+    for (int i = 0, count = child_count(); i < count; ++i) {
+      if (child_at(i)->id() != kHeaderRowId && !child_at(i)->layer())
+        child_at(i)->Paint(context);
+    }
+    // Paint header rows above other children in Z-order.
+    for (auto& header : headers_) {
+      if (!header.view->layer())
+        header.view->Paint(context);
+    }
+  }
+
+  void Layout() override {
+    views::View::Layout();
+    headers_.clear();
+    for (int i = 0, count = child_count(); i < count; ++i) {
+      views::View* header = child_at(i);
+      if (header->id() == kHeaderRowId)
+        headers_.push_back(Header(header));
+    }
+    ScrollChildren();
+  }
+
+  void ViewHierarchyChanged(
+      const ViewHierarchyChangedDetails& details) override {
+    if (!details.is_add && details.parent == this) {
+      auto header = std::find(headers_.begin(), headers_.end(), details.child);
+      if (header != headers_.end())
+        headers_.erase(header);
+    }
+  }
+
+ private:
+  class Header {
+   public:
+    Header(views::View* header) : view(header), offset(header->bounds().y()) {}
+    bool operator==(views::View* other) { return view == other; }
+
+    views::View* view;
+    int offset;
+  };
+
+  // Sets decorations on a header row to indicate whether it is sticky.
+  static void ShowHeaderSticky(views::View* header, bool show_sticky) {
+    if (show_sticky) {
+      header->SetBorder(views::Border::CreateSolidSidedBorder(
+          0, 0, kHeaderRowSeparatorThickness, 0, kHeaderRowSeparatorColor));
+    } else {
+      header->SetBorder(views::Border::CreateSolidSidedBorder(
+          kHeaderRowSeparatorThickness, 0, 0, 0, kHeaderRowSeparatorColor));
+    }
+  }
+
+  // Adjusts y-position of header rows allowing one or two rows to stick to the
+  // top of the visible viewport.
+  void ScrollChildren() {
+    const int scroll_offset = -bounds().y();
+    Header* previous_header = nullptr;
+    for (auto& header : headers_) {
+      gfx::Rect header_bounds = header.view->bounds();
+      if (scroll_offset > header.offset) {
+        header_bounds.set_y(scroll_offset);
+        header.view->SetBoundsRect(header_bounds);
+        ShowHeaderSticky(header.view, true);
+        header.view->Layout();
+        header.view->SchedulePaint();
+        if (previous_header) {
+          header_bounds = previous_header->view->bounds();
+          header_bounds.set_y(previous_header->offset);
+          previous_header->view->SetBoundsRect(header_bounds);
+          ShowHeaderSticky(previous_header->view, false);
+        }
+        previous_header = &header;
+      } else if (previous_header &&
+                 header_bounds.y() < previous_header->view->bounds().bottom()) {
+        gfx::Rect previous_header_bounds = previous_header->view->bounds();
+        previous_header_bounds.set_y(header_bounds.y() -
+                                     previous_header->view->bounds().height());
+        previous_header->view->SetBoundsRect(previous_header_bounds);
+        ShowHeaderSticky(previous_header->view, false);
+        ShowHeaderSticky(header.view, false);
+      } else {
+        ShowHeaderSticky(header.view, false);
+      }
+    }
+  }
+
+  // Header child views that stick to the top of visible viewport when scrolled.
+  std::vector<Header> headers_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScrollContentsView);
+};
 
 class ScrollSeparator : public views::View {
  public:
@@ -24,17 +136,22 @@ class ScrollSeparator : public views::View {
   ~ScrollSeparator() override {}
 
  private:
-  // Overriden from views::View.
+  // views::View.
   void OnPaint(gfx::Canvas* canvas) override {
-    canvas->FillRect(gfx::Rect(0, height() / 2, width(), 1), kBorderLightColor);
+    canvas->FillRect(gfx::Rect(0, height() / 2, width(), 1),
+                     ash::kBorderLightColor);
   }
   gfx::Size GetPreferredSize() const override {
-    return gfx::Size(1, kTrayPopupScrollSeparatorHeight);
+    return gfx::Size(1, ash::kTrayPopupScrollSeparatorHeight);
   }
 
   DISALLOW_COPY_AND_ASSIGN(ScrollSeparator);
 };
 
+}  // namespace
+
+namespace ash {
+
 class ScrollBorder : public views::Border {
  public:
   ScrollBorder() {}
@@ -43,7 +160,7 @@ class ScrollBorder : public views::Border {
   void set_visible(bool visible) { visible_ = visible; }
 
  private:
-  // Overridden from views::Border.
+  // views::Border.
   void Paint(const views::View& view, gfx::Canvas* canvas) override {
     if (!visible_)
       return;
@@ -55,7 +172,7 @@ class ScrollBorder : public views::Border {
 
   gfx::Size GetMinimumSize() const override { return gfx::Size(0, 1); }
 
-  bool visible_;
+  bool visible_ = false;
 
   DISALLOW_COPY_AND_ASSIGN(ScrollBorder);
 };
@@ -113,7 +230,7 @@ void TrayDetailsView::CreateTitleRow(int string_id) {
 
 void TrayDetailsView::CreateScrollableList() {
   DCHECK(!scroller_);
-  scroll_content_ = new views::View;
+  scroll_content_ = new ScrollContentsView(this);
   scroll_content_->SetLayoutManager(
       new views::BoxLayout(views::BoxLayout::kVertical, 0, 0, 1));
   scroller_ = new FixedSizedScrollView;