Listener & Emitter Class Example

Emitter Class

Create an emitting class having a listener_type from template sf::TListener.
Instantiate the type

class MyEmitter
{
  public:
    typedef sf::TListener<std::string&> listener_type;
    listener_type::emitter_type emitter;
 
    std::string callThem()
    {
        std::string s(1, '$');
        emitter.callListeners(s);
        return s;
    }
};

Listener Class

Derive the class from sf::ListenerList to link/register any type of listener.

class MyListener :sf::ListenerList
{
  public:
    explicit MyListener(std::string ofs)
        :offset(std::move(ofs)) {}
 
    auto unlinkIt()
    {
        return delete_null(link_ptr);
    }
 
    void linkIt(MyEmitter* emitter)
    {
        MyEmitter::listener_type::func_type lambda = [&](std::string& s)
        {
            s += offset;
        };
 
        link_ptr = emitter->emitter.linkListener(this, lambda);
    }
  
  private:  
    MyEmitter::listener_type* link_ptr{nullptr};
    std::string offset;
};