[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 70ff14fd6b4feb2838251819af30b34515ef2cf2..2e10a6167c09c371ecf615a9977e864a74af317c 100644
--- a/ash/common/system/tray/tray_details_view.cc
+++ b/ash/common/system/tray/tray_details_view.cc
@@ -16,10 +16,161 @@
 #include "ui/views/controls/scroll_view.h"
 #include "ui/views/controls/separator.h"
 #include "ui/views/layout/box_layout.h"
+#include "ui/views/view_targeter.h"
+#include "ui/views/view_targeter_delegate.h"
 
 namespace ash {
 namespace {
 
+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 until the next one "pushes" it up 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 views::ViewTargeterDelegate {
+ public:
+  ScrollContentsView() {
+    SetEventTargeter(base::MakeUnique<views::ViewTargeter>(this));
+    SetLayoutManager(
+        new views::BoxLayout(views::BoxLayout::kVertical, 0, 0, 1));
+  }
+  ~ScrollContentsView() override {}
+
+ protected:
+  // views::View:
+  void OnBoundsChanged(const gfx::Rect& previous_bounds) override {
+    PositionHeaderRows();
+  }
+
+  void PaintChildren(const ui::PaintContext& context) override {
+    for (int i = 0; i < child_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; i < child_count(); ++i) {
+      views::View* view = child_at(i);
+      if (view->id() == kHeaderRowId)
+        headers_.push_back(Header(view));
+    }
+    PositionHeaderRows();
+  }
+
+  void ViewHierarchyChanged(
+      const ViewHierarchyChangedDetails& details) override {
+    if (!details.is_add && details.parent == this) {
+      headers_.erase(std::remove_if(headers_.begin(), headers_.end(),
+                                    [details](const Header& header) {
+                                      return header.view() == details.child;
+                                    }),
+                     headers_.end());
+    }
+  }
+
+  View* TargetForRect(View* root, const gfx::Rect& rect) override {
+    // Give header rows first dibs on events.
+    for (auto& header : headers_) {
+      views::View* view = header.view();
+      gfx::Rect local_to_header = rect;
+      local_to_header.Offset(-view->x(), -view->y());
+      if (ViewTargeterDelegate::DoesIntersectRect(view, local_to_header))
+        return ViewTargeterDelegate::TargetForRect(view, local_to_header);
+    }
+    return ViewTargeterDelegate::TargetForRect(root, rect);
+  }
+
+ private:
+  // A structure that keeps the original offset of each header between the
+  // calls to Layout() to allow keeping track ofwhich view should be sticky.

[Evan Stade, 2016/11/03 19:24:31]

nit: of which

[varkha, 2016/11/03 21:29:30]

Done.

+  class Header {
+   public:
+    Header(views::View* header)
+        : view_(header), offset_(header->y()), sticky_(true) {
+      DecorateAsSticky(false);
+    }
+
+    // Sets decorations on a header row to indicate whether it is |sticky|.
+    void DecorateAsSticky(bool sticky) {
+      if (sticky_ == sticky)
+        return;
+      sticky_ = sticky;
+      if (sticky) {
+        view_->SetBorder(views::Border::CreateSolidSidedBorder(
+            0, 0, kHeaderRowSeparatorThickness, 0, kHeaderRowSeparatorColor));
+      } else {
+        view_->SetBorder(views::Border::CreateSolidSidedBorder(
+            kHeaderRowSeparatorThickness, 0, 0, 0, kHeaderRowSeparatorColor));
+      }
+    }
+
+    const views::View* view() const { return view_; }

[Evan Stade, 2016/11/03 19:24:31]

what do you need this version for?

[varkha, 2016/11/03 21:29:30]

Line 77 uses it (to keep the iterator const). Line 56 I think would be using it
as well.

+    views::View* view() {
+      return const_cast<views::View*>(const_cast<const Header*>(this)->view());
+    }
+    int offset() const { return offset_; }
+
+   private:
+    // A header View that can be decorated as sticky.
+    views::View* view_;
+
+    // Offset from the top of ScrollContentsView to |view|'s original vertical
+    // position.
+    int offset_;
+
+    // True if the header is decorated as sticky with a shadow below.
+    bool sticky_;
+  };
+
+  // Adjusts y-position of header rows allowing one or two rows to stick to the
+  // top of the visible viewport.
+  void PositionHeaderRows() {
+    const int scroll_offset = -y();
+    auto previous_header = headers_.rend();
+    for (auto header = headers_.rbegin(); header != headers_.rend(); ++header) {
+      views::View* header_view = header->view();

[Evan Stade, 2016/11/03 19:24:31]

nit: declare in the tightest scope it's needed

[varkha, 2016/11/03 21:29:30]

Done.

+      if (header->offset() < scroll_offset) {
+        if (previous_header != headers_.rend() &&
+            previous_header->view()->y() <
+                scroll_offset + header_view->height()) {
+          // Lower header displacing the header above.
+          header_view->SetY(previous_header->view()->y() -
+                            header_view->height());
+          header->DecorateAsSticky(false);
+          previous_header->DecorateAsSticky(false);
+        } else {
+          // A header becomes sticky.
+          header_view->SetY(scroll_offset);
+          header->DecorateAsSticky(true);
+          header_view->Layout();
+          header_view->SchedulePaint();
+        }
+        break;
+      } else {

[Evan Stade, 2016/11/03 19:24:32]

no else after break (I would actually invert the check and continue)

[varkha, 2016/11/03 21:29:30]

Done.

+        header->DecorateAsSticky(false);
+        previous_header = header;
+      }
+    }
+  }
+
+  // Header child views that stick to the top of visible viewport when scrolled.
+  std::vector<Header> headers_;
+
+  DISALLOW_COPY_AND_ASSIGN(ScrollContentsView);
+};
+
 // Constants for the title row in material design.
 const int kTitleRowVerticalPadding = 4;
 const int kTitleRowSeparatorBorderHeight = 1;
@@ -65,8 +216,6 @@ class TitleRowSeparatorLayout : public views::LayoutManager {
   }
 };
 
-}  // namespace
-
 class ScrollSeparator : public views::View {
  public:
   ScrollSeparator() {}
@@ -74,7 +223,7 @@ 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);
   }
@@ -85,6 +234,8 @@ class ScrollSeparator : public views::View {
   DISALLOW_COPY_AND_ASSIGN(ScrollSeparator);
 };
 
+}  // namespace
+
 class ScrollBorder : public views::Border {
  public:
   ScrollBorder() {}
@@ -93,7 +244,7 @@ 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;
@@ -105,7 +256,7 @@ 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);
 };
@@ -161,7 +312,7 @@ void TrayDetailsView::CreateTitleRow(int string_id) {
     title_row_separator_->SetLayoutManager(new TitleRowSeparatorLayout);
     views::Separator* separator =
         new views::Separator(views::Separator::HORIZONTAL);
-    separator->SetColor(ash::kTitleRowSeparatorBorderColor);
+    separator->SetColor(kTitleRowSeparatorBorderColor);
     separator->SetPreferredSize(kTitleRowSeparatorBorderHeight);
     separator->SetBorder(views::Border::CreateEmptyBorder(
         kTitleRowSeparatorHeight - kTitleRowSeparatorBorderHeight, 0, 0, 0));
@@ -181,9 +332,7 @@ void TrayDetailsView::CreateTitleRow(int string_id) {
 
 void TrayDetailsView::CreateScrollableList() {
   DCHECK(!scroller_);
-  scroll_content_ = new views::View;
-  scroll_content_->SetLayoutManager(
-      new views::BoxLayout(views::BoxLayout::kVertical, 0, 0, 1));
+  scroll_content_ = new ScrollContentsView();
   scroller_ = new FixedSizedScrollView;
   scroller_->SetContentsView(scroll_content_);