...

21 files changed, 167 insertions, 173 deletions

diff --git a/include/cru/ui/Base.h b/include/cru/ui/Base.h
index 182c00f2..b16edbfc 100644
--- a/include/cru/ui/Base.h
+++ b/include/cru/ui/Base.h
@@ -46,10 +46,6 @@ namespace host {
 class WindowHost;
 }
 
-namespace render {
-class RenderObject;
-}
-
 namespace style {
 class StyleRuleSet;
 class StyleRuleSetBind;
diff --git a/include/cru/ui/controls/Base.h b/include/cru/ui/controls/Base.h
deleted file mode 100644
index 21f1c563..00000000
--- a/include/cru/ui/controls/Base.h
+++ /dev/null
@@ -1,4 +0,0 @@
-#pragma once
-#include "../Base.h"
-
-namespace cru::ui::controls {}  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/Button.h b/include/cru/ui/controls/Button.h
index 00253793..d35d7ef8 100644
--- a/include/cru/ui/controls/Button.h
+++ b/include/cru/ui/controls/Button.h
@@ -1,19 +1,19 @@
 #pragma once
-#include "ContentControl.h"
+#include "SingleChildControl.h"
 
+#include "../controls/SingleChildControl.h"
 #include "../helper/ClickDetector.h"
+#include "../render/BorderRenderObject.h"
 #include "IBorderControl.h"
 #include "IClickableControl.h"
 #include "cru/common/Event.h"
-#include "cru/ui/render/BorderRenderObject.h"
-#include "cru/ui/style/ApplyBorderStyleInfo.h"
 
 namespace cru::ui::controls {
-class CRU_UI_API Button : public ContentControl,
+class CRU_UI_API Button : public SingleChildControl<render::BorderRenderObject>,
                           public virtual IClickableControl,
                           public virtual IBorderControl {
  public:
-  static constexpr StringView control_type = u"Button";
+  static constexpr StringView kControlType = u"Button";
 
   static Button* Create() { return new Button(); }
 
@@ -27,9 +27,7 @@ class CRU_UI_API Button : public ContentControl,
   Button& operator=(Button&& other) = delete;
   ~Button() override;
 
-  String GetControlType() const final { return control_type.ToString(); }
-
-  render::RenderObject* GetRenderObject() const override;
+  String GetControlType() const final { return kControlType.ToString(); }
 
  public:
   helper::ClickState GetClickState() override {
@@ -47,8 +45,6 @@ class CRU_UI_API Button : public ContentControl,
   void ApplyBorderStyle(const style::ApplyBorderStyleInfo& style) override;
 
  private:
-  std::unique_ptr<render::BorderRenderObject> render_object_{};
-
   helper::ClickDetector click_detector_;
 };
 }  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/Container.h b/include/cru/ui/controls/Container.h
index 926e395e..adb0fad1 100644
--- a/include/cru/ui/controls/Container.h
+++ b/include/cru/ui/controls/Container.h
@@ -1,11 +1,12 @@
 #pragma once
-#include "ContentControl.h"
+#include "SingleChildControl.h"
 
-#include "cru/ui/render/BorderRenderObject.h"
+#include "../render/BorderRenderObject.h"
 
 namespace cru::ui::controls {
-class CRU_UI_API Container : public ContentControl {
-  static constexpr StringView control_type = u"Container";
+class CRU_UI_API Container
+    : public SingleChildControl<render::BorderRenderObject> {
+  static constexpr StringView kControlType = u"Container";
 
  protected:
   Container();
@@ -17,11 +18,6 @@ class CRU_UI_API Container : public ContentControl {
   ~Container() override;
 
  public:
-  String GetControlType() const final { return control_type.ToString(); }
-
-  render::RenderObject* GetRenderObject() const override;
-
- private:
-  std::unique_ptr<render::BorderRenderObject> render_object_;
+  String GetControlType() const final { return kControlType.ToString(); }
 };
 }  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/ContentControl.h b/include/cru/ui/controls/ContentControl.h
deleted file mode 100644
index 5600ec25..00000000
--- a/include/cru/ui/controls/ContentControl.h
+++ /dev/null
@@ -1,37 +0,0 @@
-#pragma once
-#include "Control.h"
-
-
-namespace cru::ui::controls {
-class CRU_UI_API ContentControl : public Control {
- protected:
-  ContentControl() = default;
-
- public:
-  ContentControl(const ContentControl& other) = delete;
-  ContentControl(ContentControl&& other) = delete;
-  ContentControl& operator=(const ContentControl& other) = delete;
-  ContentControl& operator=(ContentControl&& other) = delete;
-  ~ContentControl() override = default;
-
-  Control* GetChild() const;
-  void SetChild(Control* child);
-
- protected:
-  virtual void OnChildChanged(Control* old_child, Control* new_child);
-
-  render::RenderObject* GetContainerRenderObject() const {
-    return container_render_object_;
-  }
-  void SetContainerRenderObject(render::RenderObject* ro) {
-    container_render_object_ = ro;
-  }
-
- private:
-  using Control::AddChild;
-  using Control::RemoveChild;
-
- private:
-  render::RenderObject* container_render_object_ = nullptr;
-};
-}  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/Control.h b/include/cru/ui/controls/Control.h
index 3927e604..9a237f8b 100644
--- a/include/cru/ui/controls/Control.h
+++ b/include/cru/ui/controls/Control.h
@@ -1,14 +1,18 @@
 #pragma once
-#include "Base.h"
-
+#include "../Base.h"
 #include "../events/UiEvents.h"
-#include "cru/common/Event.h"
-#include "cru/ui/render/RenderObject.h"
+#include "../render/RenderObject.h"
 
 namespace cru::ui::controls {
-class CRU_UI_API Control : public Object {
-  friend host::WindowHost;
 
+/**
+ *  \remarks If you want to write a new control. You should override following
+ * methods:
+ *  - GetControlType()
+ *  - ForEachChild(const std::function<void(Control*)>& predicate)
+ *  - GetRenderObject()
+ */
+class CRU_UI_API Control : public Object {
  protected:
   Control();
 
@@ -24,22 +28,12 @@ class CRU_UI_API Control : public Object {
 
   //*************** region: tree ***************
  public:
-  host::WindowHost* GetWindowHost() const;
+  virtual host::WindowHost* GetWindowHost() const;
 
   Control* GetParent() const { return parent_; }
+  void SetParent(Control* parent);
 
-  const std::vector<Control*>& GetChildren() const { return children_; }
-  Index IndexOf(Control* child) const;
-
-  // Traverse the tree rooted the control including itself.
-  void TraverseDescendants(const std::function<void(Control*)>& predicate);
-
-  bool IsAutoDeleteChildren() const { return auto_delete_children_; }
-  void SetAutoDeleteChildren(bool auto_delete_children) {
-    auto_delete_children_ = auto_delete_children;
-  }
-
-  void RemoveFromParent();
+  virtual void ForEachChild(const std::function<void(Control*)>& predicate) = 0;
 
  public:
   virtual render::RenderObject* GetRenderObject() const = 0;
@@ -135,24 +129,13 @@ class CRU_UI_API Control : public Object {
 
   //*************** region: tree ***************
  protected:
-  void AddChild(Control* control, Index position);
-  void RemoveChild(Index position);
-  virtual void OnAddChild(Control* child, Index position);
-  virtual void OnRemoveChild(Control* child, Index position);
   virtual void OnParentChanged(Control* old_parent, Control* new_parent);
-  virtual void OnAttachToHost(host::WindowHost* host);
-  virtual void OnDetachFromHost(host::WindowHost* host);
 
  protected:
   virtual void OnMouseHoverChange(bool newHover) { CRU_UNUSED(newHover) }
 
  private:
   Control* parent_ = nullptr;
-  std::vector<Control*> children_;
-
-  host::WindowHost* window_host_ = nullptr;
-
-  bool auto_delete_children_ = true;
 
  private:
   bool is_mouse_over_ = false;
diff --git a/include/cru/ui/controls/FlexLayout.h b/include/cru/ui/controls/FlexLayout.h
index 8fdb3aef..15494742 100644
--- a/include/cru/ui/controls/FlexLayout.h
+++ b/include/cru/ui/controls/FlexLayout.h
@@ -10,9 +10,10 @@ using render::FlexCrossAlignment;
 using render::FlexDirection;
 using render::FlexMainAlignment;
 
-class CRU_UI_API FlexLayout : public LayoutControl {
+class CRU_UI_API FlexLayout
+    : public LayoutControl<render::FlexLayoutRenderObject> {
  public:
-  static constexpr StringView control_type = u"FlexLayout";
+  static constexpr StringView kControlType = u"FlexLayout";
 
   static FlexLayout* Create() { return new FlexLayout(); }
 
@@ -26,9 +27,7 @@ class CRU_UI_API FlexLayout : public LayoutControl {
   FlexLayout& operator=(FlexLayout&& other) = delete;
   ~FlexLayout() override;
 
-  String GetControlType() const final { return control_type.ToString(); }
-
-  render::RenderObject* GetRenderObject() const override;
+  String GetControlType() const final { return kControlType.ToString(); }
 
   FlexMainAlignment GetContentMainAlign() const;
   void SetContentMainAlign(FlexMainAlignment value);
@@ -38,11 +37,5 @@ class CRU_UI_API FlexLayout : public LayoutControl {
 
   FlexCrossAlignment GetItemCrossAlign() const;
   void SetItemCrossAlign(FlexCrossAlignment alignment);
-
-  FlexChildLayoutData GetChildLayoutData(Control* control);
-  void SetChildLayoutData(Control* control, FlexChildLayoutData data);
-
- private:
-  std::shared_ptr<render::FlexLayoutRenderObject> render_object_;
 };
 }  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/IBorderControl.h b/include/cru/ui/controls/IBorderControl.h
index 3178d7f2..f8f2f88d 100644
--- a/include/cru/ui/controls/IBorderControl.h
+++ b/include/cru/ui/controls/IBorderControl.h
@@ -1,6 +1,5 @@
 #pragma once
 #include "../style/ApplyBorderStyleInfo.h"
-#include "Base.h"
 #include "cru/common/Base.h"
 
 namespace cru::ui::controls {
diff --git a/include/cru/ui/controls/IClickableControl.h b/include/cru/ui/controls/IClickableControl.h
index 48b3ad5f..67fa43ab 100644
--- a/include/cru/ui/controls/IClickableControl.h
+++ b/include/cru/ui/controls/IClickableControl.h
@@ -1,8 +1,7 @@
 #pragma once
-#include "Base.h"
 
+#include "../helper/ClickDetector.h"
 #include "cru/common/Event.h"
-#include "cru/ui/helper/ClickDetector.h"
 
 namespace cru::ui::controls {
 struct CRU_UI_API IClickableControl : virtual Interface {
diff --git a/include/cru/ui/controls/LayoutControl.h b/include/cru/ui/controls/LayoutControl.h
index 639ecc74..b42cfc9a 100644
--- a/include/cru/ui/controls/LayoutControl.h
+++ b/include/cru/ui/controls/LayoutControl.h
@@ -2,11 +2,12 @@
 #include "Control.h"
 
 namespace cru::ui::controls {
+template <typename TRenderObject>
 class CRU_UI_API LayoutControl : public Control {
  protected:
-  LayoutControl() = default;
-  explicit LayoutControl(render::RenderObject* container_render_object)
-      : container_render_object_(container_render_object) {}
+  LayoutControl() : container_render_object_(new TRenderObject()) {
+    container_render_object_->SetAttachedControl(this);
+  }
 
  public:
   LayoutControl(const LayoutControl& other) = delete;
@@ -15,23 +16,54 @@ class CRU_UI_API LayoutControl : public Control {
   LayoutControl& operator=(LayoutControl&& other) = delete;
   ~LayoutControl() override = default;
 
-  using Control::AddChild;
-  using Control::RemoveChild;
+ public:
+  void ForEachChild(const std::function<void(Control*)>& callback) override {
+    for (auto child : children_) {
+      callback(child);
+    }
+  }
 
-  void ClearChildren();
+  render::RenderObject* GetRenderObject() const override {
+    return container_render_object_.get();
+  }
 
- protected:
-  // If container render object is not null. Render object of added or removed
-  // child control will automatically sync to the container render object.
-  render::RenderObject* GetContainerRenderObject() const;
-  void SetContainerRenderObject(render::RenderObject* ro) {
-    container_render_object_ = ro;
+  TRenderObject* GetContainerRenderObject() const {
+    return container_render_object_.get();
+  }
+
+  void AddChild(Control* child, Index position) {
+    Expects(child);
+    Expects(child->GetParent() == nullptr);
+    if (position < 0) position = 0;
+    if (position > children_.size()) position = children_.size();
+    children_.insert(children_.begin() + position, child);
+    child->SetParent(this);
+
+    assert(child->GetRenderObject());
+    container_render_object_->AddChild(child->GetRenderObject(), position);
+  }
+
+  void RemoveChild(Index position) {
+    if (position < 0 || position >= children_.size()) return;
+    auto child = children_[position];
+    children_.erase(children_.begin() + position);
+    child->SetParent(nullptr);
+    container_render_object_->RemoveChild(position);
   }
 
-  void OnAddChild(Control* child, Index position) override;
-  void OnRemoveChild(Control* child, Index position) override;
+  const typename TRenderObject::ChildLayoutData& GetChildLayoutData(
+      Index position) {
+    return container_render_object_->GetChildLayoutDataAt(position);
+  }
+
+  void SetChildLayoutData(Index position,
+                          typename TRenderObject::ChildLayoutData data) {
+    container_render_object_->SetChildLayoutDataAt(position, data);
+  }
 
  private:
-  render::RenderObject* container_render_object_ = nullptr;
+  std::unique_ptr<TRenderObject> container_render_object_;
+
+  std::vector<Control*> children_;
 };
 }  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/NoChildControl.h b/include/cru/ui/controls/NoChildControl.h
index 6d2168cb..1b864b20 100644
--- a/include/cru/ui/controls/NoChildControl.h
+++ b/include/cru/ui/controls/NoChildControl.h
@@ -13,8 +13,7 @@ class CRU_UI_API NoChildControl : public Control {
   NoChildControl& operator=(NoChildControl&& other) = delete;
   ~NoChildControl() override = default;
 
- private:
-  using Control::AddChild;
-  using Control::RemoveChild;
+ public:
+  void ForEachChild(const std::function<void(Control*)>& callback) override;
 };
-}  // namespace cru::ui
+}  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/RootControl.h b/include/cru/ui/controls/RootControl.h
index 41424286..a1878836 100644
--- a/include/cru/ui/controls/RootControl.h
+++ b/include/cru/ui/controls/RootControl.h
@@ -1,16 +1,14 @@
 #pragma once
 #include "LayoutControl.h"
 
-#include "cru/common/Base.h"
 #include "cru/common/Event.h"
-#include "cru/platform/gui/Base.h"
 #include "cru/platform/gui/Window.h"
-#include "cru/ui/Base.h"
 #include "cru/ui/host/WindowHost.h"
 #include "cru/ui/render/StackLayoutRenderObject.h"
 
 namespace cru::ui::controls {
-class CRU_UI_API RootControl : public LayoutControl {
+class CRU_UI_API RootControl
+    : public LayoutControl<render::StackLayoutRenderObject> {
  protected:
   explicit RootControl(Control* attached_control);
 
@@ -20,7 +18,9 @@ class CRU_UI_API RootControl : public LayoutControl {
   ~RootControl() override;
 
  public:
-  render::RenderObject* GetRenderObject() const override;
+  host::WindowHost* GetWindowHost() const override {
+    return window_host_.get();
+  }
 
   platform::gui::INativeWindow* GetNativeWindow();
 
@@ -30,8 +30,6 @@ class CRU_UI_API RootControl : public LayoutControl {
  private:
   std::unique_ptr<host::WindowHost> window_host_;
 
-  std::unique_ptr<render::StackLayoutRenderObject> render_object_;
-
   Control* attached_control_;
 
   EventRevokerListGuard
diff --git a/include/cru/ui/controls/ScrollView.h b/include/cru/ui/controls/ScrollView.h
index 7bc9b226..43b6390c 100644
--- a/include/cru/ui/controls/ScrollView.h
+++ b/include/cru/ui/controls/ScrollView.h
@@ -1,33 +1,26 @@
 #pragma once
-#include "ContentControl.h"
-#include "cru/common/Base.h"
-#include "cru/ui/render/RenderObject.h"
+#include "SingleChildControl.h"
 
 #include "cru/ui/render/ScrollRenderObject.h"
 
-#include <memory>
-#include <string_view>
-
 namespace cru::ui::controls {
-class CRU_UI_API ScrollView : public ContentControl {
+class CRU_UI_API ScrollView
+    : public SingleChildControl<render::ScrollRenderObject> {
  public:
   static ScrollView* Create() { return new ScrollView(); }
 
-  static constexpr StringView control_type = u"ScrollView";
+  static constexpr StringView kControlType = u"ScrollView";
 
+ protected:
   ScrollView();
 
+ public:
   CRU_DELETE_COPY(ScrollView)
   CRU_DELETE_MOVE(ScrollView)
 
-  ~ScrollView() override = default;
+  ~ScrollView() override;
 
  public:
-  String GetControlType() const override { return control_type.ToString(); }
-
-  render::RenderObject* GetRenderObject() const override;
-
- private:
-  std::unique_ptr<render::ScrollRenderObject> scroll_render_object_;
+  String GetControlType() const override { return kControlType.ToString(); }
 };
 }  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/SingleChildControl.h b/include/cru/ui/controls/SingleChildControl.h
new file mode 100644
index 00000000..037d6dd3
--- /dev/null
+++ b/include/cru/ui/controls/SingleChildControl.h
@@ -0,0 +1,55 @@
+#pragma once
+#include "Control.h"
+
+namespace cru::ui::controls {
+template <typename TRenderObject>
+class CRU_UI_API SingleChildControl : public Control {
+ protected:
+  SingleChildControl() : container_render_object_(new TRenderObject()) {
+    container_render_object_->SetAttachedControl(this);
+  }
+
+ public:
+  CRU_DELETE_COPY(SingleChildControl)
+  CRU_DELETE_MOVE(SingleChildControl)
+
+  ~SingleChildControl() override {}
+
+  Control* GetChild() const { return child_; }
+  void SetChild(Control* child) {
+    if (child == child_) return;
+
+    assert(child == nullptr || child->GetParent() == nullptr);
+
+    if (child_) {
+      child_->SetParent(nullptr);
+    }
+
+    child_ = child;
+
+    if (child) {
+      child->SetParent(this);
+    }
+
+    container_render_object_->SetChild(child->GetRenderObject());
+  }
+
+  render::RenderObject* GetRenderObject() const override {
+    return container_render_object_.get();
+  }
+
+  TRenderObject* GetContainerRenderObject() const {
+    return container_render_object_.get();
+  }
+
+  void ForEachChild(const std::function<void(Control*)>& predicate) override {
+    if (child_) {
+      predicate(child_);
+    }
+  }
+
+ private:
+  Control* child_;
+  std::unique_ptr<TRenderObject> container_render_object_;
+};
+}  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/StackLayout.h b/include/cru/ui/controls/StackLayout.h
index 36e8ab43..28e0e796 100644
--- a/include/cru/ui/controls/StackLayout.h
+++ b/include/cru/ui/controls/StackLayout.h
@@ -1,11 +1,13 @@
 #pragma once
 #include "LayoutControl.h"
-#include "cru/ui/Base.h"
+
+#include "../render/StackLayoutRenderObject.h"
 
 namespace cru::ui::controls {
-class CRU_UI_API StackLayout : public LayoutControl {
+class CRU_UI_API StackLayout
+    : public LayoutControl<render::StackLayoutRenderObject> {
  public:
-  static constexpr StringView control_type = u"StackLayout";
+  static constexpr StringView kControlType = u"StackLayout";
 
   static StackLayout* Create() { return new StackLayout(); }
 
@@ -18,14 +20,6 @@ class CRU_UI_API StackLayout : public LayoutControl {
 
   ~StackLayout() override;
 
-  String GetControlType() const final { return control_type.ToString(); }
-
-  render::RenderObject* GetRenderObject() const override;
-
-  const StackChildLayoutData& GetChildLayoutData(Index position);
-  void SetChildLayoutData(Index position, StackChildLayoutData data);
-
- private:
-  std::shared_ptr<render::StackLayoutRenderObject> render_object_;
+  String GetControlType() const final { return kControlType.ToString(); }
 };
 }  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/TextBlock.h b/include/cru/ui/controls/TextBlock.h
index 3f87d96c..feb5cfa3 100644
--- a/include/cru/ui/controls/TextBlock.h
+++ b/include/cru/ui/controls/TextBlock.h
@@ -8,7 +8,7 @@ namespace cru::ui::controls {
 class CRU_UI_API TextBlock : public NoChildControl,
                              public virtual ITextHostControl {
  public:
-  static constexpr StringView control_type = u"TextBlock";
+  static constexpr StringView kControlType = u"TextBlock";
 
   static TextBlock* Create();
   static TextBlock* Create(String text, bool selectable = false);
@@ -23,7 +23,7 @@ class CRU_UI_API TextBlock : public NoChildControl,
   TextBlock& operator=(TextBlock&& other) = delete;
   ~TextBlock() override;
 
-  String GetControlType() const final { return control_type.ToString(); }
+  String GetControlType() const final { return kControlType.ToString(); }
 
   render::RenderObject* GetRenderObject() const override;
 
diff --git a/include/cru/ui/controls/TextBox.h b/include/cru/ui/controls/TextBox.h
index 10f67b72..0632cc12 100644
--- a/include/cru/ui/controls/TextBox.h
+++ b/include/cru/ui/controls/TextBox.h
@@ -1,6 +1,7 @@
 #pragma once
 #include "NoChildControl.h"
 
+#include "../render/BorderRenderObject.h"
 #include "../render/TextRenderObject.h"
 #include "IBorderControl.h"
 #include "TextHostControlService.h"
diff --git a/include/cru/ui/controls/TextHostControlService.h b/include/cru/ui/controls/TextHostControlService.h
index 67b075c5..0d4a20cf 100644
--- a/include/cru/ui/controls/TextHostControlService.h
+++ b/include/cru/ui/controls/TextHostControlService.h
@@ -1,6 +1,4 @@
 #pragma once
-#include "Base.h"
-
 #include "../render/TextRenderObject.h"
 #include "cru/platform/gui/InputMethod.h"
 #include "cru/platform/gui/TimerHelper.h"
diff --git a/include/cru/ui/events/MouseEventArgs.h b/include/cru/ui/events/MouseEventArgs.h
index 11ce6463..1320002d 100644
--- a/include/cru/ui/events/MouseEventArgs.h
+++ b/include/cru/ui/events/MouseEventArgs.h
@@ -1,6 +1,8 @@
 #pragma once
 #include "UiEventArgs.h"
 
+#include "../render/RenderObject.h"
+
 #include <optional>
 
 namespace cru::ui::events {
diff --git a/include/cru/ui/host/WindowHost.h b/include/cru/ui/host/WindowHost.h
index 80076afd..1de915e0 100644
--- a/include/cru/ui/host/WindowHost.h
+++ b/include/cru/ui/host/WindowHost.h
@@ -1,6 +1,7 @@
 #pragma once
 #include "../Base.h"
 
+#include "../render/RenderObject.h"
 #include "cru/common/Event.h"
 #include "cru/platform/gui/Cursor.h"
 #include "cru/platform/gui/UiApplication.h"
diff --git a/include/cru/ui/render/LayoutRenderObject.h b/include/cru/ui/render/LayoutRenderObject.h
index 62ee9005..d6882f9a 100644
--- a/include/cru/ui/render/LayoutRenderObject.h
+++ b/include/cru/ui/render/LayoutRenderObject.h
@@ -11,7 +11,7 @@ class CRU_UI_API LayoutRenderObject : public RenderObject {
 
  private:
   struct ChildData {
-    RenderObject* child;
+    RenderObject* render_object;
     ChildLayoutData layout_data;
   };
 
@@ -43,19 +43,19 @@ class CRU_UI_API LayoutRenderObject : public RenderObject {
     children_.erase(children_.begin() + position);
   }
 
-  void SetChildLayoutData(Index position, ChildLayoutData data) {
+  const ChildLayoutData& GetChildLayoutDataAt(Index position) const {
     Expects(position >= 0 && position < GetChildCount());
-    children_[position].layout_data = std::move(data);
-    InvalidateLayout();
+    return children_[position].layout_data;
   }
 
-  const ChildLayoutData& GetChildLayoutData(Index position) const {
+  void SetChildLayoutDataAt(Index position, ChildLayoutData data) {
     Expects(position >= 0 && position < GetChildCount());
-    return children_[position].layout_data;
+    children_[position].layout_data = std::move(data);
+    InvalidateLayout();
   }
 
   void Draw(platform::graphics::IPainter* painter) override {
-    for (auto& child : children_) {
+    for (const auto& child : children_) {
       painter->PushState();
       painter->ConcatTransform(
           Matrix::Translation(child.render_object->GetOffset()));