...

39 files changed, 210 insertions, 450 deletions

diff --git a/demos/main/main.cpp b/demos/main/main.cpp
index 38fad739..41320858 100644
--- a/demos/main/main.cpp
+++ b/demos/main/main.cpp
@@ -14,11 +14,7 @@
 #include "cru/ui/host/WindowHost.h"
 
 using cru::platform::gui::IUiApplication;
-using cru::ui::controls::Button;
-using cru::ui::controls::FlexLayout;
-using cru::ui::controls::TextBlock;
-using cru::ui::controls::TextBox;
-using cru::ui::controls::Window;
+using namespace cru::ui::controls;
 
 int main() {
   IUiApplication* application = cru::platform::bootstrap::CreateUiApplication();
@@ -40,9 +36,9 @@ int main() {
   const auto window = Window::Create();
 
   const auto flex_layout = FlexLayout::Create();
-  flex_layout->SetFlexDirection(cru::ui::FlexDirection::Vertical);
-  flex_layout->SetContentMainAlign(cru::ui::FlexCrossAlignment::Center);
-  flex_layout->SetItemCrossAlign(cru::ui::FlexCrossAlignment::Center);
+  flex_layout->SetFlexDirection(FlexDirection::Vertical);
+  flex_layout->SetContentMainAlign(FlexCrossAlignment::Center);
+  flex_layout->SetItemCrossAlign(FlexCrossAlignment::Center);
 
   window->AddChild(flex_layout, 0);
 
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()));
diff --git a/src/ui/CMakeLists.txt b/src/ui/CMakeLists.txt
index d358940f..98d21c9e 100644
--- a/src/ui/CMakeLists.txt
+++ b/src/ui/CMakeLists.txt
@@ -5,10 +5,8 @@ add_library(cru_ui SHARED
 	components/Menu.cpp
 	controls/Button.cpp
 	controls/Container.cpp
-	controls/ContentControl.cpp
 	controls/Control.cpp
 	controls/FlexLayout.cpp
-	controls/LayoutControl.cpp
 	controls/NoChildControl.cpp
 	controls/Popup.cpp
 	controls/RootControl.cpp
diff --git a/src/ui/components/Menu.cpp b/src/ui/components/Menu.cpp
index c6db8e4a..3134bbb6 100644
--- a/src/ui/components/Menu.cpp
+++ b/src/ui/components/Menu.cpp
@@ -33,7 +33,7 @@ void MenuItem::SetText(String text) { text_->SetText(std::move(text)); }
 
 Menu::Menu() {
   container_ = controls::FlexLayout::Create();
-  container_->SetFlexDirection(FlexDirection::Vertical);
+  container_->SetFlexDirection(controls::FlexDirection::Vertical);
 }
 
 Menu::~Menu() {
diff --git a/src/ui/controls/Button.cpp b/src/ui/controls/Button.cpp
index e42bfae7..d7d157c5 100644
--- a/src/ui/controls/Button.cpp
+++ b/src/ui/controls/Button.cpp
@@ -10,11 +10,7 @@
 
 namespace cru::ui::controls {
 Button::Button() : click_detector_(this) {
-  render_object_ = std::make_unique<render::BorderRenderObject>();
-  render_object_->SetAttachedControl(this);
-  SetContainerRenderObject(render_object_.get());
-  render_object_->SetBorderEnabled(true);
-
+  GetContainerRenderObject()->SetBorderEnabled(true);
   auto default_button_style =
       ThemeManager::GetInstance()->GetResourceStyleRuleSet(u"button.style");
   GetStyleRuleSet()->SetParent(std::move(default_button_style));
@@ -22,11 +18,7 @@ Button::Button() : click_detector_(this) {
 
 Button::~Button() = default;
 
-render::RenderObject* Button::GetRenderObject() const {
-  return render_object_.get();
-}
-
 void Button::ApplyBorderStyle(const style::ApplyBorderStyleInfo& style) {
-  render_object_->ApplyBorderStyle(style);
+  GetContainerRenderObject()->ApplyBorderStyle(style);
 }
 }  // namespace cru::ui::controls
diff --git a/src/ui/controls/Container.cpp b/src/ui/controls/Container.cpp
index 92ac3847..7b0c10a9 100644
--- a/src/ui/controls/Container.cpp
+++ b/src/ui/controls/Container.cpp
@@ -5,16 +5,7 @@
 #include "cru/ui/render/RenderObject.h"
 
 namespace cru::ui::controls {
-Container::Container() {
-  render_object_ = std::make_unique<render::BorderRenderObject>();
-  render_object_->SetBorderEnabled(false);
-  render_object_->SetAttachedControl(this);
-  SetContainerRenderObject(render_object_.get());
-}
+Container::Container() {}
 
 Container::~Container() = default;
-
-render::RenderObject* Container::GetRenderObject() const {
-  return render_object_.get();
-}
 }  // namespace cru::ui::controls
diff --git a/src/ui/controls/ContentControl.cpp b/src/ui/controls/ContentControl.cpp
deleted file mode 100644
index 8b421e09..00000000
--- a/src/ui/controls/ContentControl.cpp
+++ /dev/null
@@ -1,31 +0,0 @@
-#include "cru/ui/controls/ContentControl.h"
-
-namespace cru::ui::controls {
-Control* ContentControl::GetChild() const {
-  if (GetChildren().empty()) return nullptr;
-  return GetChildren()[0];
-}
-
-void ContentControl::SetChild(Control* child) {
-  Control* old_child = nullptr;
-  if (!GetChildren().empty()) {
-    old_child = GetChildren()[0];
-    this->RemoveChild(0);
-  }
-  if (child) {
-    this->AddChild(child, 0);
-  }
-  OnChildChanged(old_child, child);
-}
-
-void ContentControl::OnChildChanged(Control* old_child, Control* new_child) {
-  if (container_render_object_) {
-    if (old_child) {
-      container_render_object_->RemoveChild(0);
-    }
-    if (new_child) {
-      container_render_object_->AddChild(new_child->GetRenderObject(), 0);
-    }
-  }
-}
-}  // namespace cru::ui::controls
diff --git a/src/ui/controls/Control.cpp b/src/ui/controls/Control.cpp
index 36d5cd60..df71f660 100644
--- a/src/ui/controls/Control.cpp
+++ b/src/ui/controls/Control.cpp
@@ -31,31 +31,21 @@ Control::Control() {
   });
 }
 
-Control::~Control() {
-  if (auto_delete_children_) {
-    for (const auto child : children_) {
-      delete child;
-    }
-  }
-}
-
-host::WindowHost* Control::GetWindowHost() const { return window_host_; }
+Control::~Control() {}
 
-Index Control::IndexOf(Control* child) const {
-  for (Index i = 0; i < children_.size(); ++i) {
-    if (children_[i] == child) return i;
+host::WindowHost* Control::GetWindowHost() const {
+  auto parent = GetParent();
+  if (parent) {
+    return parent->GetWindowHost();
   }
-  return -1;
+  return nullptr;
 }
 
-void Control::TraverseDescendants(
-    const std::function<void(Control*)>& predicate) {
-  predicate(this);
-  for (auto c : GetChildren()) c->TraverseDescendants(predicate);
-}
-
-void Control::RemoveFromParent() {
-  if (parent_) parent_->RemoveChild(parent_->IndexOf(this));
+void Control::SetParent(Control* parent) {
+  if (parent_ == parent) return;
+  auto old_parent = parent_;
+  parent_ = parent;
+  OnParentChanged(old_parent, parent);
 }
 
 bool Control::HasFocus() {
@@ -117,65 +107,4 @@ void Control::SetCursor(std::shared_ptr<ICursor> cursor) {
 std::shared_ptr<style::StyleRuleSet> Control::GetStyleRuleSet() {
   return style_rule_set_;
 }
-
-void Control::AddChild(Control* control, const Index position) {
-  Expects(control->GetParent() ==
-          nullptr);  // The control already has a parent.
-  Expects(position >= 0);
-  Expects(position <= static_cast<Index>(
-                          children_.size()));  // The position is out of range.
-
-  children_.insert(children_.cbegin() + position, control);
-
-  const auto old_parent = control->parent_;
-  control->parent_ = this;
-
-  OnAddChild(control, position);
-  control->OnParentChanged(old_parent, this);
-
-  if (window_host_)
-    control->TraverseDescendants([this](Control* control) {
-      control->window_host_ = window_host_;
-      control->OnAttachToHost(window_host_);
-    });
-}
-
-void Control::RemoveChild(const Index position) {
-  Expects(position >= 0);
-  Expects(position < static_cast<Index>(
-                         children_.size()));  // The position is out of range.
-
-  const auto i = children_.cbegin() + position;
-  const auto control = *i;
-
-  children_.erase(i);
-  control->parent_ = nullptr;
-
-  OnRemoveChild(control, position);
-  control->OnParentChanged(this, nullptr);
-
-  if (window_host_)
-    control->TraverseDescendants([this](Control* control) {
-      control->window_host_ = nullptr;
-      control->OnDetachFromHost(window_host_);
-    });
-}
-
-void Control::OnAddChild(Control* child, Index position) {
-  CRU_UNUSED(child)
-  CRU_UNUSED(position)
-}
-void Control::OnRemoveChild(Control* child, Index position) {
-  CRU_UNUSED(child)
-  CRU_UNUSED(position)
-}
-
-void Control::OnParentChanged(Control* old_parent, Control* new_parent) {
-  CRU_UNUSED(old_parent)
-  CRU_UNUSED(new_parent)
-}
-
-void Control::OnAttachToHost(host::WindowHost* host) { CRU_UNUSED(host) }
-
-void Control::OnDetachFromHost(host::WindowHost* host) { CRU_UNUSED(host) }
 }  // namespace cru::ui::controls
diff --git a/src/ui/controls/FlexLayout.cpp b/src/ui/controls/FlexLayout.cpp
index ecf4d428..8d71cfdb 100644
--- a/src/ui/controls/FlexLayout.cpp
+++ b/src/ui/controls/FlexLayout.cpp
@@ -1,70 +1,31 @@
 #include "cru/ui/controls/FlexLayout.h"
 
 namespace cru::ui::controls {
-using render::FlexLayoutRenderObject;
-
-FlexLayout::FlexLayout() {
-  render_object_.reset(new FlexLayoutRenderObject());
-  render_object_->SetAttachedControl(this);
-  SetContainerRenderObject(render_object_.get());
-}
+FlexLayout::FlexLayout() = default;
 
 FlexLayout::~FlexLayout() = default;
 
-render::RenderObject* FlexLayout::GetRenderObject() const {
-  return render_object_.get();
-}
-
-namespace {
-Index FindPosition(render::RenderObject* parent, render::RenderObject* child) {
-  const auto& render_objects = parent->GetChildren();
-  const auto find_result =
-      std::find(render_objects.cbegin(), render_objects.cend(), child);
-  if (find_result == render_objects.cend()) {
-    throw std::logic_error("Control is not a child of FlexLayout.");
-  }
-  return static_cast<Index>(find_result - render_objects.cbegin());
-}
-}  // namespace
-
-FlexChildLayoutData FlexLayout::GetChildLayoutData(Control* control) {
-  Expects(control);
-  return render_object_->GetChildLayoutData(
-      FindPosition(render_object_.get(), control->GetRenderObject()));
-}
-
-void FlexLayout::SetChildLayoutData(Control* control,
-                                    FlexChildLayoutData data) {
-  Expects(control);
-  render_object_->SetChildLayoutData(
-      FindPosition(render_object_.get(), control->GetRenderObject()),
-      std::move(data));
-}
-
 FlexMainAlignment FlexLayout::GetContentMainAlign() const {
-  return render_object_->GetContentMainAlign();
+  return GetContainerRenderObject()->GetContentMainAlign();
 }
 
 void FlexLayout::SetContentMainAlign(FlexMainAlignment value) {
-  if (value == GetContentMainAlign()) return;
-  render_object_->SetContentMainAlign(value);
+  GetContainerRenderObject()->SetContentMainAlign(value);
 }
 
 FlexDirection FlexLayout::GetFlexDirection() const {
-  return render_object_->GetFlexDirection();
+  return GetContainerRenderObject()->GetFlexDirection();
 }
 
 void FlexLayout::SetFlexDirection(FlexDirection direction) {
-  if (direction == GetFlexDirection()) return;
-  render_object_->SetFlexDirection(direction);
+  GetContainerRenderObject()->SetFlexDirection(direction);
 }
 
 FlexCrossAlignment FlexLayout::GetItemCrossAlign() const {
-  return render_object_->GetItemCrossAlign();
+  return GetContainerRenderObject()->GetItemCrossAlign();
 }
 
 void FlexLayout::SetItemCrossAlign(FlexCrossAlignment alignment) {
-  if (alignment == GetItemCrossAlign()) return;
-  render_object_->SetItemCrossAlign(alignment);
+  GetContainerRenderObject()->SetItemCrossAlign(alignment);
 }
 }  // namespace cru::ui::controls
diff --git a/src/ui/controls/LayoutControl.cpp b/src/ui/controls/LayoutControl.cpp
deleted file mode 100644
index 5c67bc86..00000000
--- a/src/ui/controls/LayoutControl.cpp
+++ /dev/null
@@ -1,24 +0,0 @@
-#include "cru/ui/controls/LayoutControl.h"
-
-#include "cru/ui/render/RenderObject.h"
-
-namespace cru::ui::controls {
-void LayoutControl::ClearChildren() {
-  while (GetChildren().size() > 0) {
-    RemoveChild(0);
-  }
-}
-
-void LayoutControl::OnAddChild(Control* child, Index position) {
-  if (container_render_object_ != nullptr) {
-    container_render_object_->AddChild(child->GetRenderObject(), position);
-  }
-}
-
-void LayoutControl::OnRemoveChild(Control* child, Index position) {
-  CRU_UNUSED(child)
-  if (container_render_object_ != nullptr) {
-    container_render_object_->RemoveChild(position);
-  }
-}
-}  // namespace cru::ui::controls
diff --git a/src/ui/controls/NoChildControl.cpp b/src/ui/controls/NoChildControl.cpp
index 29177828..4a9002ed 100644
--- a/src/ui/controls/NoChildControl.cpp
+++ b/src/ui/controls/NoChildControl.cpp
@@ -1,3 +1,8 @@
 #include "cru/ui/controls/NoChildControl.h"
 
-namespace cru::ui::controls {}
+namespace cru::ui::controls {
+void NoChildControl::ForEachChild(
+    const std::function<void(Control*)>& callback) {
+  CRU_UNUSED(callback);
+}
+}  // namespace cru::ui::controls
diff --git a/src/ui/controls/RootControl.cpp b/src/ui/controls/RootControl.cpp
index 828822c6..07647024 100644
--- a/src/ui/controls/RootControl.cpp
+++ b/src/ui/controls/RootControl.cpp
@@ -12,21 +12,14 @@
 namespace cru::ui::controls {
 RootControl::RootControl(Control* attached_control)
     : attached_control_(attached_control) {
-  render_object_ = std::make_unique<render::StackLayoutRenderObject>();
-  render_object_->SetAttachedControl(this);
-  render_object_->SetDefaultHorizontalAlignment(Alignment::Stretch);
-  render_object_->SetDefaultVertialAlignment(Alignment::Stretch);
-  SetContainerRenderObject(render_object_.get());
+  GetContainerRenderObject()->SetDefaultHorizontalAlignment(Alignment::Stretch);
+  GetContainerRenderObject()->SetDefaultVertialAlignment(Alignment::Stretch);
   window_host_ = std::make_unique<host::WindowHost>(this);
   window_host_->SetLayoutPreferToFillWindow(true);
 }
 
 RootControl::~RootControl() {}
 
-render::RenderObject* RootControl::GetRenderObject() const {
-  return render_object_.get();
-}
-
 platform::gui::INativeWindow* RootControl::GetNativeWindow() {
   return window_host_->GetNativeWindow();
 }
diff --git a/src/ui/controls/ScrollView.cpp b/src/ui/controls/ScrollView.cpp
index e87ede4b..f3b3750f 100644
--- a/src/ui/controls/ScrollView.cpp
+++ b/src/ui/controls/ScrollView.cpp
@@ -1,19 +1,7 @@
 #include "cru/ui/controls/ScrollView.h"
 
-#include "cru/ui/render/RenderObject.h"
-#include "cru/ui/render/ScrollRenderObject.h"
-
-#include <memory>
-
 namespace cru::ui::controls {
-ScrollView::ScrollView() {
-  scroll_render_object_ = std::make_unique<render::ScrollRenderObject>();
-  scroll_render_object_->SetAttachedControl(this);
-
-  SetContainerRenderObject(scroll_render_object_.get());
-}
+ScrollView::ScrollView() {}
 
-render::RenderObject* ScrollView::GetRenderObject() const {
-  return scroll_render_object_.get();
-}
+ScrollView::~ScrollView() {}
 }  // namespace cru::ui::controls
diff --git a/src/ui/controls/StackLayout.cpp b/src/ui/controls/StackLayout.cpp
index 7e45a555..55964bcd 100644
--- a/src/ui/controls/StackLayout.cpp
+++ b/src/ui/controls/StackLayout.cpp
@@ -1,29 +1,9 @@
 #include "cru/ui/controls/StackLayout.h"
-#include <memory>
-
-#include "cru/ui/render/StackLayoutRenderObject.h"
 
 namespace cru::ui::controls {
 using render::StackLayoutRenderObject;
 
-StackLayout::StackLayout() {
-  render_object_ = std::make_unique<StackLayoutRenderObject>();
-  render_object_->SetAttachedControl(this);
-  SetContainerRenderObject(render_object_.get());
-}
+StackLayout::StackLayout() = default;
 
 StackLayout::~StackLayout() = default;
-
-render::RenderObject* StackLayout::GetRenderObject() const {
-  return render_object_.get();
-}
-
-const StackChildLayoutData& StackLayout::GetChildLayoutData(Index position) {
-  return render_object_->GetChildLayoutData(position);
-}
-
-void StackLayout::SetChildLayoutData(Index position,
-                                     StackChildLayoutData data) {
-  render_object_->SetChildLayoutData(position, std::move(data));
-}
 }  // namespace cru::ui::controls
diff --git a/src/ui/controls/TextBox.cpp b/src/ui/controls/TextBox.cpp
index 11b77e99..66b6bd43 100644
--- a/src/ui/controls/TextBox.cpp
+++ b/src/ui/controls/TextBox.cpp
@@ -24,8 +24,8 @@ TextBox::TextBox()
       theme_manager->GetResourceBrush(u"text.caret.brush"));
   text_render_object_->SetEditMode(true);
 
-  border_render_object_->AddChild(scroll_render_object_.get(), 0);
-  scroll_render_object_->AddChild(text_render_object_.get(), 0);
+  border_render_object_->SetChild(scroll_render_object_.get());
+  scroll_render_object_->SetChild(text_render_object_.get());
 
   border_render_object_->SetAttachedControl(this);
   scroll_render_object_->SetAttachedControl(this);
diff --git a/src/ui/controls/Window.cpp b/src/ui/controls/Window.cpp
index 998395f3..6891c918 100644
--- a/src/ui/controls/Window.cpp
+++ b/src/ui/controls/Window.cpp
@@ -1,12 +1,5 @@
 #include "cru/ui/controls/Window.h"
 
-#include "cru/common/Base.h"
-#include "cru/platform/gui/Base.h"
-#include "cru/ui/controls/RootControl.h"
-#include "cru/ui/host/WindowHost.h"
-#include "cru/ui/render/Base.h"
-#include "cru/ui/render/StackLayoutRenderObject.h"
-
 namespace cru::ui::controls {
 Window* Window::Create(Control* attached_control) {
   return new Window(attached_control);
diff --git a/src/ui/host/WindowHost.cpp b/src/ui/host/WindowHost.cpp
index 9773c117..6849d000 100644
--- a/src/ui/host/WindowHost.cpp
+++ b/src/ui/host/WindowHost.cpp
@@ -105,11 +105,6 @@ inline void BindNativeEvent(
 
 WindowHost::WindowHost(controls::Control* root_control)
     : root_control_(root_control), focus_control_(root_control) {
-  root_control_->TraverseDescendants([this](controls::Control* control) {
-    control->window_host_ = this;
-    control->OnAttachToHost(this);
-  });
-
   root_render_object_ = root_control->GetRenderObject();
 
   this->layout_paint_cycler_ = std::make_unique<LayoutPaintCycler>(this);
diff --git a/src/ui/render/FlexLayoutRenderObject.cpp b/src/ui/render/FlexLayoutRenderObject.cpp
index ebe60395..6475d005 100644
--- a/src/ui/render/FlexLayoutRenderObject.cpp
+++ b/src/ui/render/FlexLayoutRenderObject.cpp
@@ -333,7 +333,7 @@ Size FlexLayoutRenderObject::OnMeasureContent(
   std::vector<FlexChildLayoutData> layout_data_list;
   for (int i = 0; i < GetChildCount(); i++) {
     children.push_back(GetChildAt(i));
-    layout_data_list.push_back(GetChildLayoutData(i));
+    layout_data_list.push_back(GetChildLayoutDataAt(i));
   }
 
   if (horizontal) {
@@ -353,7 +353,7 @@ void FlexLayoutRenderObject::OnLayoutContent(const Rect& content_rect) {
   std::vector<FlexChildLayoutData> layout_data_list;
   for (int i = 0; i < child_count; i++) {
     children.push_back(GetChildAt(i));
-    layout_data_list.push_back(GetChildLayoutData(i));
+    layout_data_list.push_back(GetChildLayoutDataAt(i));
   }
 
   if (direction_ == FlexDirection::Horizontal) {
diff --git a/src/ui/render/StackLayoutRenderObject.cpp b/src/ui/render/StackLayoutRenderObject.cpp
index 6c79716f..fda9a420 100644
--- a/src/ui/render/StackLayoutRenderObject.cpp
+++ b/src/ui/render/StackLayoutRenderObject.cpp
@@ -35,7 +35,7 @@ Size StackLayoutRenderObject::OnMeasureContent(
   child_max_size = Max(requirement.min.GetSizeOr0(), child_max_size);
 
   for (Index i = 0; i < GetChildCount(); ++i) {
-    auto child_layout_data = GetChildLayoutData(i);
+    auto child_layout_data = GetChildLayoutDataAt(i);
     auto horizontal_stretch =
         child_layout_data.horizontal.value_or(default_horizontal_alignment_) ==
         Alignment::Stretch;
@@ -67,7 +67,7 @@ void StackLayoutRenderObject::OnLayoutContent(const Rect& content_rect) {
 
   for (int i = 0; i < count; i++) {
     const auto child = GetChildAt(i);
-    const auto& layout_data = GetChildLayoutData(i);
+    const auto& layout_data = GetChildLayoutDataAt(i);
     const auto& size = child->GetDesiredSize();
     child->Layout(Point{
         CalculateAnchorByAlignment(