Combining function, bind, c++ and managed code

Question

I have a c++ function which is expecting a function object (AuthenticateNotifyFunc) to be passed to it thus:

class lc_Authenticate
{
public:
   typedef enum {
     kAbort,
     kContinue
   } lc_AuthenticateStatus;

   typedef std::tr1::function<lc_AuthenticateStatus (const string &msg)> AuthenticateNotifyFunc;

   bool Authenticate(lc_AuthenticateParams &params,
                     AuthenticateNotifyFunc notifyFunc);
}

Within a managed c++ project, I am attempting to define a parameter to pass to the above function thus:

public ref class Form1 : public System::Windows::Forms::Form
{
    public:
    lc_Authenticate::lc_AuthenticateStatus UpdateStatus(const string &msg)
    {
        <<DO SOMETHING>>
        return(lc_Authenticate::kContinue);
    }
    void test()
    {
        string appKey, appSecret;
        appKey = GetString(this->appKeyTextBox->Text);
        appSecret = GetString(this->appSecretTextBox->Text);

        lc_Authenticate dbauth;
        lc_AuthenticateParams params(appKey, appSecret);

        //  DOESN'T COMPILE won't let me take address of member function
        // or know about _1
        lc_Authenticate::AuthenticateNotifyFunc func =
            std::tr1::bind(&Form1::UpdateStatus, this, _1);

        dbauth.Authenticate(params, func);
    }
};

So I am trying to implement a generic method of passing a function to a c++ method in such a way that it doesn't care whether the passed function is static or a member function. And I'm not clear how do do this from managed code.

Answer 1

You cannot bind to an instance method of a managed class by design. The garbage collector moves the object around when compacting the heap, causing this to change. You'll need to use a managed delegate. So you can't avoid a native helper class that provides the stable callback you need for your function<>. You can get back to managed code from there with Marshal::GetFunctionPointerForDelegate().