Question

I make a interface class in C++ for voice recognition, i´m using the Julius API. http://julius.sourceforge.jp/en_index.php?q=index-en.html.

Well, my class has some events, these events will be triggered by the Julius API.
The Julius API has the function call callback_add with this signature:

int callback_add (Recog *recog, int code, void(*func)(Recog *recog, void *data), void data)

I using some ‘proxy’ functions to Invoke the events and passing this functions to callback_add.

If the property event is static, it works fine, but if is a non static, inside the proxy function the property not be recognized.

The difficult is because I have to use the callback_add function and can’t modify this.

Here is a summary of the class with 2 events (static and non-static)

Header

#ifndef FALAENGINE_H_
#define FALAENGINE_H_

#pragma once

extern "C"{
#include <julius/julius.h>
}

namespace FalaAPI {

    public ref class FalaEngine
    {
    public:
        FalaEngine();
        ~FalaEngine();

        // Events
        delegate void OnRecognizedDele(FalaAPI::RecoResult^ result);
        static property OnRecognizedDele^ OnRecognized;

        delegate void OnEngineStartDele();
        property OnEngineStartDele^ OnEngineStart;

    private:
        Recog *recog;
        Jconf *jconf;
    };
}

#endif /* FALAENGINE_H_*/

Source

#include "stdafx.h"

using System::String;
using System::Console;

#include "FalaEngine.h"
#include <windows.h>

namespace FalaAPI{
    void StartOnEngineStart()(Recog *recog, void * dummy){
        if(FalaEngine::OnEngineStart->GetInvocationList()->Length > 0)
            FalaEngine::OnEngineStart->Invoke();
    }

    void StartOnRecognized()(Recog *recog, void * dummy){
        if(FalaEngine::OnRecognized->GetInvocationList()->Length > 0)
            FalaEngine::OnRecognized->Invoke();
    }

    FalaEngine::FalaEngine(){
        recog = j_recog_new();
        jconf = j_jconf_new();

        //Julius callback Functions
        callback_add(recog, CALLBACK_EVENT_PROCESS_ONLINE, StartOnEngineStart, NULL);

        callback_add(recog, CALLBACK_RESULT, StartOnRecognized, NULL);
    }
}

The problem occurs inside StartOnEngineStart function:

error C2227: left of ‘->GetInvocationList’ must point to class/struct/union/generic type

Answer 1

A non-static member exists separately in each instance. You haven’t specified which instance contains the delegate you want to inspect, you’ve only specified a class (and there may be many instances).

Try using the dummy parameter to pass your instance. But be careful, because the garbage collector will move objects around unless you have pinned them, so simply passing the address will not work. You need to create and pass a GCHandle instead. (Be careful not to leak the GCHandle, or your object will never be released)

---

Something like this should be effective:

ref class FalaEngine;

struct EngineHandle
{
    gcroot<FalaEngine^> handle;
    EngineHandle(FalaEngine^ engine) : handle(engine) {}
};

public ref class FalaEngine
{
    clr_scoped_ptr<EngineHandle> callback_ptr;
public:
    FalaEngine();
    ~FalaEngine();

    // Events
    delegate void OnRecognizedDele(FalaAPI::RecoResult^ result);
    property OnRecognizedDele^ OnRecognized;


    delegate void OnEngineStartDele();
    property OnEngineStartDele^ OnEngineStart;

private:
    Recog *recog;
    Jconf *jconf;
};

void StartOnEngineStart(Recog *recog, void * dummy)
{
    FalaEngine^ that = static_cast<EngineHandle*>(dummy)->handle;
    that->OnEngineStart(); // C++/CLI already checks if the invocation list is empty
}


void StartOnRecognized(Recog *recog, void * dummy)
{
    FalaEngine^ that = static_cast<EngineHandle*>(dummy)->handle;
    that->OnRecognized(recog->get_result());
}

FalaEngine::FalaEngine()
    : callback_ptr(new EngineHandle(this))
{
    recog = j_recog_new();
    jconf = j_jconf_new();


    //Julius callback Functions
    callback_add(recog, CALLBACK_EVENT_PROCESS_ONLINE, StartOnEngineStart, callback_ptr.get());

    callback_add(recog, CALLBACK_RESULT, StartOnRecognized, callback_ptr.get());

}

The clr_scoped_ptr class is here. There are not many license requirements, make sure you follow them though if you use it.