Experimental alignment layout manager using a property on the views

ui/views/attributes.h

Index: ui/views/attributes.h
diff --git a/ui/views/attributes.h b/ui/views/attributes.h
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+// Copyright (c) 2016 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_VIEWS_ATTRIBUTES_H_
+#define UI_VIEWS_ATTRIBUTES_H_
+
+#include <algorithm>
+#include <cmath>
+#include <map>
+#include <memory>
+#include <string>
+#include <utility>
+
+#include "base/macros.h"
+#include "base/memory/ptr_util.h"
+#include "ui/views/views_export.h"
+
+namespace views {
+
+class View;
+
+using AttributeId = void*;
+
+template <typename T>
+class AttributeIdHelper {
+ public:
+  static AttributeId GetAttributeId() {
+    return T::TYPE_NOT_AVAILABLE();
+  }
+};
+
+template <typename T>
+AttributeId GetAttributeId() {
+  return AttributeIdHelper<T>::GetAttributeId();
+}
+
+#define _REGISTER_ATTRIBUTE_ID(T)                                         \
+template <>                                                               \
+class AttributeIdHelper<T> {                                              \
+ public:                                                                  \
+  static AttributeId GetAttributeId() {                                   \
+    static const AttributeId id = AttributeIdFactory::GetAttributeId(#T); \
+    return id;                                                            \
+  }                                                                       \
+}
+
+#define REGISTER_ATTRIBUTE_ID(T) _REGISTER_ATTRIBUTE_ID(T)
+
+class VIEWS_EXPORT AttributeIdFactory {
+ public:
+  static AttributeId GetAttributeId(const char* typeName);
+ private:
+  class AttributeIdHolder {
+   public:
+    AttributeIdHolder() { attribute_id_ = static_cast<AttributeId>(this); }
+    AttributeId GetAttributeId() { return attribute_id_; }
+   private:
+    AttributeId attribute_id_;
+  };
+  AttributeIdFactory() {}
+  using AttributeIdMap =
+    std::map<std::string, std::unique_ptr<AttributeIdHolder>>;
+  static AttributeIdMap map_;
+  DISALLOW_COPY_AND_ASSIGN(AttributeIdFactory);
+};
+
+class VIEWS_EXPORT Attribute {
+ public:
+  enum class NotifyType {
+    AttributeAdded,
+    AttributeRemoved,
+  };
+  Attribute() : view_(nullptr) {};
+  virtual ~Attribute() {};
+  void AddedToView(View *view) { view_ = view; }
+  template <class T> T* AsAttribute() {
+    if (Identity() == GetAttributeId<T>())
+      return static_cast<T*>(this);
+    return nullptr;
+  }
+  virtual AttributeId Identity() const;
+  View *view() { return view_; }
+  virtual void Notification(NotifyType type, Attribute *attribute) {}
+  void RemovedFromView() { view_ = nullptr; }
+  virtual void ViewNotification(View* view) {}
+ private:
+  View *view_;
+  DISALLOW_COPY_AND_ASSIGN(Attribute);
+};
+
+REGISTER_ATTRIBUTE_ID(Attribute);
+
+template <class Content, class A = Attribute>
+class CustomAttribute : public A {
+  static_assert(std::is_base_of<Attribute, A>::value,
+                "'A' must derive from Attribute");
+ public:
+  CustomAttribute() {};
+  CustomAttribute(const Content& content) : content_(content) {}
+  ~CustomAttribute() override {};
+  inline Content& GetContent() { return content_; }
+  AttributeId Identity() const override {
+    return GetAttributeId<CustomAttribute<Content, A>>();
+  }
+ private:
+  Content content_;
+  CustomAttribute(const CustomAttribute&) = delete;
+  void operator=(const CustomAttribute&) = delete;
+};
+
+class VIEWS_EXPORT AttributeContainer {
+ public:
+  AttributeContainer(View *view);
+  ~AttributeContainer();
+  template <class T> bool Add(std::unique_ptr<T> attribute) {
+    AttributeId attributeId = GetAttributeId<T>();
+    T* attr = attribute.get();
+    if (map_.insert(AttributeMap::value_type(attributeId,
+        std::move(attribute))).second) {
+      Notification(Attribute::NotifyType::AttributeAdded, attr);
+      if (view_) {
+        attribute->AddedToView(view_);
+        attribute->ViewNotification(view_);
+      }
+      return true;
+    }
+    return false;
+  }
+  bool Remove(const AttributeId AttributeId);
+  template <class T> bool Find(T*& attribute) {
+    static_assert(std::is_base_of<Attribute, T>::value,
+      "'T' must derive from Attribute");
+    AttributeMap::iterator it = map_.find(GetAttributeId<T>());
+    bool found = it != map_.end();
+    if (found) {
+      Attribute* a = it->second.get();
+      if (a)
+        attribute = a->AsAttribute<T>();
+      else
+        found = false;
+    }
+    return found;
+  }
+  void ViewNotification(View *view);
+ private:
+  AttributeContainer();
+  void Notification(Attribute::NotifyType type, Attribute *attribute);
+  using AttributeMap = std::map<AttributeId, std::unique_ptr<Attribute>>;
+  AttributeMap map_;
+  View *view_;
+  DISALLOW_COPY_AND_ASSIGN(AttributeContainer);
+};
+
+} // namespace views
+
+#endif  // UI_VIEWS_ATTRIBUTES_H_