websockettpp回调(通过函数指针的Class方法）

我举了这个例子https://github.com/zaphoyd/websocketpp/blob/develop/examples/testee_server/testee_server.cpp并创建了一个简单的类，如下所示：

namespace __webauth__ {
struct ws_config: public websocketpp::config::asio {
    // pull default settings from our core config
    typedef websocketpp::config::asio core;
    typedef core::concurrency_type concurrency_type;
    typedef core::request_type request_type;
    typedef core::response_type response_type;
    typedef core::message_type message_type;
    typedef core::con_msg_manager_type con_msg_manager_type;
    typedef core::endpoint_msg_manager_type endpoint_msg_manager_type;
    typedef core::alog_type alog_type;
    typedef core::elog_type elog_type;
    typedef core::rng_type rng_type;
    typedef core::endpoint_base endpoint_base;
    static bool const enable_multithreading = true;
    struct transport_config: public core::transport_config {
        typedef core::concurrency_type concurrency_type;
        typedef core::elog_type elog_type;
        typedef core::alog_type alog_type;
        typedef core::request_type request_type;
        typedef core::response_type response_type;
        static bool const enable_multithreading = true;
    };
    typedef websocketpp::transport::asio::endpoint<transport_config> transport_type;
    static const websocketpp::log::level elog_level =
            websocketpp::log::elevel::none;
    static const websocketpp::log::level alog_level =
            websocketpp::log::alevel::none;
    /// permessage_compress extension
    struct permessage_deflate_config {
    };
    typedef websocketpp::extensions::permessage_deflate::enabled<
            permessage_deflate_config> permessage_deflate_type;
};
typedef websocketpp::server<ws_config> server;
// use placeholders
using websocketpp::lib::placeholders::_1;
using websocketpp::lib::placeholders::_2;
using websocketpp::lib::bind;
// define message type
typedef server::message_ptr message_ptr;
// define property tree (JSON)
using boost::property_tree::ptree;
using boost::property_tree::basic_ptree;
class Dispatcher {
public:
    void start();
private:
    server dispatcher;       // Create a server endpoint
    short dport = 8888;
    // callbacks
    void on_message(server* s, websocketpp::connection_hdl hdl, message_ptr msg);
};
} // end webauth namespace

但是，当我尝试从start（）成员函数调用on_message回调时，如下所示：

dispatcher.set_message_handler（绑定（&on\ymessage，&dispatcher，：：_1，：：_2））

I get the following error:
Multiple markers at this line
    - required from here
    - ISO C++ forbids taking the address of an unqualified or parenthesized non-static member function to form a pointer to 
     member function. Say ‘&__webauth__::Dispatcher::on_message’ [-fpermissive]
    - candidate is:
    - no matching function for call to 
     ‘websocketpp::server<__webauth__::ws_config>::set_message_handler(boost::_bi::bind_t<boost::_bi::unspecified, void 
     (__webauth__::Dispatcher::*)(websocketpp::server<__webauth__::ws_config>*, std::weak_ptr<void>, 
     std::shared_ptr<websocketpp::message_buffer::message<websocketpp::message_buffer::alloc::con_msg_manager> >), 
     boost::_bi::list3<boost::_bi::value<websocketpp::server<__webauth__::ws_config>*>, boost::arg<1>, boost::arg<2> > >)’

我知道我需要通过函数指针正确地调用类方法，但我不知道如何在我创建的类中调用on_message回调。有人知道如何完成这项任务吗？

这是start（）函数：

// ********************
//  Dispatcher (Public)
// ********************
void Dispatcher::start() {
    info("Dispatcher::start");
    try {
        // Total silence
        dispatcher.clear_access_channels(websocketpp::log::alevel::all);
        dispatcher.clear_error_channels(websocketpp::log::alevel::all);
        // Initialize ASIO
        dispatcher.init_asio();
        dispatcher.set_reuse_addr(true);
        // Register our message handler
       dispatcher.set_message_handler(bind(&on_message,&dispatcher,::_1,::_2));
        // Listen on specified port with extended listen backlog
        dispatcher.set_listen_backlog(8192);
        dispatcher.listen(dport);
        // Start the dispatcher accept loop
        dispatcher.start_accept();
        typedef websocketpp::lib::shared_ptr<websocketpp::lib::thread> thread_ptr;
        thread_ptr ts;
        ts = websocketpp::lib::make_shared<websocketpp::lib::thread>(&server::run, &dispatcher);
        ts->join();
    } catch (websocketpp::exception const & e) {
        std::cout << "exception: " << e.what() << std::endl;
    }
}