[Vince]

Intriguing question. Something like this might work. Haven't tested it, though.

PHP код:

public OnTrailerUpdate(playerid, vehicleid)
{
    // vehicleid is the id of the trailer
    new playerVehicle = GetPlayerVehicleID(playerid);
    
    if(playerVehicle) 
    {
        static attachedTrailer[MAX_VEHICLES]; 
        new currentTrailer = GetVehicleTrailer(playerVehicle);
        
        if(currentTrailer == vehicleid && attachedTrailer[playerVehicle] == 0)
        {
            OnVehicleTrailerAttached(playerVehicle, playerid, vehicleid);
            attachedTrailer[playerVehicle] = vehicleid;
        }
        else if(currentTrailer == 0 && attachedTrailer[playerVehicle] == vehicleid)
        {
            OnVehicleTrailerDetached(playerVehicle, playerid, vehicleid);
            attachedTrailer[playerVehicle] = 0;
        }
    }
    return 1;
}
OnVehicleTrailerAttached(vehicleid, playerid, trailerid)
{
    printf("new trailer with id %d attached to vehicle %d, driven by %d", trailerid, vehicleid, playerid);
}
OnVehicleTrailerDetached(vehicleid, playerid, oldtrailerid)
{
    printf("old trailer with id %d detached from vehicle %d, driven by %d", oldtrailerid, vehicleid, playerid);
} 


Important to note is that these custom callbacks will only get called if the player that sends those updates is actually in the driver's cabine. A trailer can also be connected by pushing it but in that case this custom callback will not fire until someone actually enters the driver's cabin.