Add index to EntryState

include/ftxui/component/component_base.hpp

@@ -44,6 +44,7 @@ class ComponentBase {
   ComponentBase* Parent() const;
   Component& ChildAt(size_t i);
   size_t ChildCount() const;
+  int IndexOf(ComponentBase* child) const;
   void Add(Component children);
   void Detach();
   void DetachAllChildren();

include/ftxui/component/component_options.hpp

@@ -25,6 +25,7 @@ struct EntryState {
   bool state;         ///< The state of the button/checkbox/radiobox
   bool active;        ///< Whether the entry is the active one.
   bool focused;       ///< Whether the entry is one focused by the user.
+  int index;          ///< Index of the entry when applicable or -1.
 };
 
 struct UnderlineOption {

src/ftxui/component/button.cpp

@@ -53,6 +53,7 @@ class ButtonBase : public ComponentBase, public ButtonOption {
         false,
         active,
         focused_or_hover,
+        -1,
     };
 
     auto element = (transform ? transform : DefaultTransform)  //

src/ftxui/component/checkbox.cpp

@@ -32,6 +32,7 @@ class CheckboxBase : public ComponentBase, public CheckboxOption {
         *checked,
         is_active,
         is_focused || hovered_,
+        -1,
     };
     auto element = (transform ? transform : CheckboxOption::Simple().transform)(
         entry_state);

src/ftxui/component/component.cpp

@@ -51,6 +51,18 @@ size_t ComponentBase::ChildCount() const {
   return children_.size();
 }
 
+/// @brief Return index of child or -1 if not found.
+/// @ingroup component
+int ComponentBase::IndexOf(ComponentBase* child) const {
+  int index = 0;
+  for (Component c : children_) {
+    if (&(*c) == child)
+      return index;
+    index++;
+  }
+  return -1;
+}
+
 /// @brief Add a child.
 /// @@param child The child to be attached.
 /// @ingroup component

src/ftxui/component/menu.cpp

@@ -127,6 +127,7 @@ class MenuBase : public ComponentBase, public MenuOption {
           false,
           is_selected,
           is_focused,
+          i,
       };
 
       auto focus_management = (selected_focus_ != i) ? nothing
@@ -630,6 +631,7 @@ Component MenuEntry(MenuEntryOption option) {
           false,
           hovered_,
           focused,
+          Parent()->IndexOf(this),
       };
 
       const Element element =

src/ftxui/component/menu_test.cpp

@@ -226,5 +226,52 @@ TEST(MenuTest, AnimationsVertical) {
   }
 }
 
+TEST(MenuTest, EntryIndex) {
+  int selected = 0;
+  std::vector<std::string> entries = {"0", "1", "2"};
+
+  auto option = MenuOption::Vertical();
+  option.entries = &entries;
+  option.selected = &selected;
+  option.entries_option.transform = [&](const EntryState& state) {
+    int curidx = std::stoi(state.label);
+    EXPECT_EQ(state.index, curidx);
+    return text(state.label);
+  };
+  auto menu = Menu(option);
+  menu->OnEvent(Event::ArrowDown);
+  menu->OnEvent(Event::ArrowDown);
+  menu->OnEvent(Event::Return);
+  entries.resize(2);
+  (void)menu->Render();
+}
+
+TEST(MenuTest, MenuEntryIndex) {
+  int selected = 0;
+
+  MenuEntryOption option;
+  option.transform = [&](const EntryState& state) {
+    int curidx = std::stoi(state.label);
+    EXPECT_EQ(state.index, curidx);
+    return text(state.label);
+  };
+  auto menu = Container::Vertical(
+      {
+          MenuEntry("0", option),
+          MenuEntry("1", option),
+          MenuEntry("2", option),
+      },
+      &selected);
+
+  menu->OnEvent(Event::ArrowDown);
+  menu->OnEvent(Event::ArrowDown);
+  menu->OnEvent(Event::Return);
+  for(int idx = 0; idx < menu->ChildCount(); idx++)
+  {
+    auto child = menu->ChildAt(idx);
+    EXPECT_EQ(menu->IndexOf(&(*child)), idx);  
+  }
+}
+
 }  // namespace ftxui
 // NOLINTEND

src/ftxui/component/radiobox.cpp

@@ -44,6 +44,7 @@ class RadioboxBase : public ComponentBase, public RadioboxOption {
           selected() == i,
           is_selected,
           is_focused,
+          i,
       };
       auto element =
           (transform ? transform : RadioboxOption::Simple().transform)(state);