Wt

#include <Wt/WApplication.h>

#include <Wt/WContainerWidget.h>

#include <Wt/WMenu.h>

#include <Wt/WStackedWidget.h>

#include <Wt/WText.h>

#include <Wt/WTextEdit.h>

#include <functional>

#include <memory>

class DeferredWidget final : public Wt::WContainerWidget {

public:

  using WidgetCreator = std::function<std::unique_ptr<Wt::WWidget>()>;

  explicit DeferredWidget(WidgetCreator f);

  ~DeferredWidget() override;

  void load() override;

private:

  WidgetCreator f_;

};

DeferredWidget::DeferredWidget(WidgetCreator f)

  : f_(std::move(f))

{ }

DeferredWidget::~DeferredWidget() = default;

void DeferredWidget::load()

{

  if (!loaded()) {

    addWidget(f_());

  }

  WContainerWidget::load();

}

class Application final : public Wt::WApplication

{

public:

  explicit Application(const Wt::WEnvironment &env);

  ~Application() override;

};

Application::Application(const Wt::WEnvironment &env)

  : Wt::WApplication(env)

{

  auto stack = root()->addNew<Wt::WStackedWidget>();

  auto menu = root()->insertNew<Wt::WMenu>(0, stack);

  menu->addItem(Wt::utf8("One"), std::make_unique<DeferredWidget>([]{

    return std::make_unique<Wt::WText>(Wt::utf8("One"));

  }));

  menu->addItem(Wt::utf8("Two"), std::make_unique<DeferredWidget>([]{

    return std::make_unique<Wt::WText>(Wt::utf8("Two"));

  }));

  menu->addItem(Wt::utf8("WTextEdit"), std::make_unique<DeferredWidget>([]{

    auto container = std::make_unique<Wt::WContainerWidget>();

    auto textEdit = container->addNew<Wt::WTextEdit>();

    textEdit->resize(400, 300);

    return container;

  }));

}

Application::~Application() = default;

int main(int argc, char *argv[])

{

  return Wt::WRun(argc, argv, [](const Wt::WEnvironment &env) {

    return std::make_unique<Application>(env);

  });

}