6 files changed, 91 insertions, 33 deletions
diff --git a/include/cru/ui/controls/Control.h b/include/cru/ui/controls/Control.h
index 9a237f8b..242db3f4 100644
--- a/include/cru/ui/controls/Control.h
+++ b/include/cru/ui/controls/Control.h
@@ -10,6 +10,7 @@ namespace cru::ui::controls {
  * methods:
  *  - GetControlType()
  *  - ForEachChild(const std::function<void(Control*)>& predicate)
+ *  - RemoveChild(Control* child)
  *  - GetRenderObject()
  */
 class CRU_UI_API Control : public Object {
@@ -35,6 +36,14 @@ class CRU_UI_API Control : public Object {
 
   virtual void ForEachChild(const std::function<void(Control*)>& predicate) = 0;
 
+  /**
+   *  \remarks This method should be permissive, which means if the specified
+   * child control is not a real child of this then nothing will be done.
+   */
+  virtual void RemoveChild(Control* child) = 0;
+
+  void RemoveFromParent();
+
  public:
   virtual render::RenderObject* GetRenderObject() const = 0;
 
@@ -129,7 +138,7 @@ class CRU_UI_API Control : public Object {
 
   //*************** region: tree ***************
  protected:
-  virtual void OnParentChanged(Control* old_parent, Control* new_parent);
+  virtual void OnParentChanged(Control* old_parent, Control* new_parent) {}
 
  protected:
   virtual void OnMouseHoverChange(bool newHover) { CRU_UNUSED(newHover) }
diff --git a/include/cru/ui/controls/LayoutControl.h b/include/cru/ui/controls/LayoutControl.h
index b42cfc9a..59ffaee2 100644
--- a/include/cru/ui/controls/LayoutControl.h
+++ b/include/cru/ui/controls/LayoutControl.h
@@ -17,12 +17,30 @@ class CRU_UI_API LayoutControl : public Control {
   ~LayoutControl() override = default;
 
  public:
+  const std::vector<Control*>& GetChildren() const { return children_; }
+  Index GetChildCount() const { return children_.size(); }
+  Control* GetChild(Index index) const { return children_[index]; }
+  Index IndexOf(Control* control) const {
+    auto it = std::find(children_.begin(), children_.end(), control);
+    if (it == children_.end()) {
+      return -1;
+    }
+    return it - children_.begin();
+  }
+
   void ForEachChild(const std::function<void(Control*)>& callback) override {
     for (auto child : children_) {
       callback(child);
     }
   }
 
+  void RemoveChild(Control* child) override {
+    auto index = IndexOf(child);
+    if (index != -1) {
+      RemoveChildAt(index);
+    }
+  }
+
   render::RenderObject* GetRenderObject() const override {
     return container_render_object_.get();
   }
@@ -31,7 +49,7 @@ class CRU_UI_API LayoutControl : public Control {
     return container_render_object_.get();
   }
 
-  void AddChild(Control* child, Index position) {
+  void AddChildAt(Control* child, Index position) {
     Expects(child);
     Expects(child->GetParent() == nullptr);
     if (position < 0) position = 0;
@@ -43,7 +61,9 @@ class CRU_UI_API LayoutControl : public Control {
     container_render_object_->AddChild(child->GetRenderObject(), position);
   }
 
-  void RemoveChild(Index position) {
+  void AddChild(Control* child) { AddChildAt(child, GetChildCount()); }
+
+  void RemoveChildAt(Index position) {
     if (position < 0 || position >= children_.size()) return;
     auto child = children_[position];
     children_.erase(children_.begin() + position);
@@ -51,6 +71,14 @@ class CRU_UI_API LayoutControl : public Control {
     container_render_object_->RemoveChild(position);
   }
 
+  void ClearChildren() {
+    for (auto child : children_) {
+      child->SetParent(nullptr);
+    }
+    children_.clear();
+    container_render_object_->ClearChildren();
+  }
+
   const typename TRenderObject::ChildLayoutData& GetChildLayoutData(
       Index position) {
     return container_render_object_->GetChildLayoutDataAt(position);
diff --git a/include/cru/ui/controls/NoChildControl.h b/include/cru/ui/controls/NoChildControl.h
index 1b864b20..f22fd85e 100644
--- a/include/cru/ui/controls/NoChildControl.h
+++ b/include/cru/ui/controls/NoChildControl.h
@@ -15,5 +15,7 @@ class CRU_UI_API NoChildControl : public Control {
 
  public:
   void ForEachChild(const std::function<void(Control*)>& callback) override;
+
+  void RemoveChild(Control* child) override;
 };
 }  // namespace cru::ui::controls
diff --git a/include/cru/ui/controls/SingleChildControl.h b/include/cru/ui/controls/SingleChildControl.h
index 037d6dd3..d40d7a27 100644
--- a/include/cru/ui/controls/SingleChildControl.h
+++ b/include/cru/ui/controls/SingleChildControl.h
@@ -48,8 +48,14 @@ class CRU_UI_API SingleChildControl : public Control {
     }
   }
 
+  void RemoveChild(Control* child) override {
+    if (child_ == child) {
+      SetChild(nullptr);
+    }
+  }
+
  private:
-  Control* child_;
+  Control* child_ = nullptr;
   std::unique_ptr<TRenderObject> container_render_object_;
 };
 }  // namespace cru::ui::controls
diff --git a/include/cru/ui/render/LayoutRenderObject.h b/include/cru/ui/render/LayoutRenderObject.h
index d6882f9a..c8678deb 100644
--- a/include/cru/ui/render/LayoutRenderObject.h
+++ b/include/cru/ui/render/LayoutRenderObject.h
@@ -26,7 +26,7 @@ class CRU_UI_API LayoutRenderObject : public RenderObject {
 
   Index GetChildCount() const { return static_cast<Index>(children_.size()); }
   RenderObject* GetChildAt(Index position) {
-    Expects(position > 0 && position < GetChildCount());
+    Expects(position >= 0 && position < GetChildCount());
     return children_[position].render_object;
   }
   void AddChild(RenderObject* render_object, Index position) {
@@ -35,12 +35,22 @@ class CRU_UI_API LayoutRenderObject : public RenderObject {
     children_.insert(children_.begin() + position,
                      ChildData{render_object, ChildLayoutData()});
     render_object->SetParent(this);
+    InvalidateLayout();
   }
 
   void RemoveChild(Index position) {
     Expects(position > 0 && position < GetChildCount());
     children_[position].render_object->SetParent(nullptr);
     children_.erase(children_.begin() + position);
+    InvalidateLayout();
+  }
+
+  void ClearChildren() {
+    for (auto child : children_) {
+      child.render_object->SetParent(nullptr);
+    }
+    children_.clear();
+    InvalidateLayout();
   }
 
   const ChildLayoutData& GetChildLayoutDataAt(Index position) const {
diff --git a/include/cru/ui/render/RenderObject.h b/include/cru/ui/render/RenderObject.h
index cfa72b7d..bef2859e 100644
--- a/include/cru/ui/render/RenderObject.h
+++ b/include/cru/ui/render/RenderObject.h
@@ -5,34 +5,36 @@
 #include "cru/common/String.h"
 
 namespace cru::ui::render {
-// Render object will not destroy its children when destroyed. Control must
-// manage lifecycle of its render objects. Since control will destroy its
-// children when destroyed, render objects will be destroyed along with it.
-//
-// About layout:
-// Render object should be able to deal with arbitrary size as the result of
-// measure and layout.
-//
-// Parent may pass calculated preferred size down. But the preferred size set on
-// child itself takes precedence.
-//
-// Each render object should obey the measure requirement to set size and report
-// a warning when that requirement can't be satisfied with probably bigger size
-// of children than that of itself and optional visual effect to indicate that.
-//
-// If size of chilren are less than min size requirement, then render object
-// should try to fill the rest area. If size of children are more than max size
-// requirement, then render object should display a warning of the layout
-// problem and use the max size of itself with children exceeding its bound.
-// (Or better you could use some visual effect to indicate that.)
-//
-// To write a custom RenderObject, override following methods:
-// public:
-//  void Draw(platform::graphics::IPainter* painter) override;
-//  RenderObject* HitTest(const Point& point) override;
-// protected:
-//  Size OnMeasureContent(const MeasureRequirement& requirement) override;
-//  void OnLayoutContent(const Rect& content_rect) override;
+/**
+ * ### Layout
+ *
+ * Render object should be able to deal with _arbitrary_ size as the result of
+ * measure and layout.
+ *
+ * Parent may pass calculated preferred size down. But the preferred size set on
+ * child itself takes precedence.
+ *
+ * Each render object should obey the measure requirement to set size and report
+ * a warning when that requirement can't be satisfied with probably bigger size
+ * of children than that of itself and optional visual effect to indicate that.
+ *
+ * If size of chilren are less than min size requirement, then render object
+ * should try to fill the rest area. If size of children are more than max size
+ * requirement, then render object should display a warning of the layout
+ * problem and use the max size of itself with children exceeding its bound.
+ * (Or better you could use some visual effect to indicate that.)
+ *
+ * ### Create New Render Object
+ *
+ * To write a custom RenderObject, override following methods:
+ *
+ * public:
+ *  void Draw(platform::graphics::IPainter* painter) override;
+ *  RenderObject* HitTest(const Point& point) override;
+ * protected:
+ *  Size OnMeasureContent(const MeasureRequirement& requirement) override;
+ *  void OnLayoutContent(const Rect& content_rect) override;
+ */
 class CRU_UI_API RenderObject : public Object {
   CRU_DEFINE_CLASS_LOG_TAG(u"cru::ui::render::RenderObject")
 
@@ -137,6 +139,7 @@ class CRU_UI_API RenderObject : public Object {
 
   virtual void OnAttachedControlChanged(controls::Control* old_control,
                                         controls::Control* new_control) {}
+
   virtual void OnResize(const Size& new_size) {}
 
  private: