[yezizhu]

Nothing wrong with the code.
Try to check debug info.

Код:

public OnPlayerEnterVehicle(playerid, vehicleid, ispassenger)
{
  printf("_%d_",IsTrailerAttachedToVehicle(vehicleid));
  if(IsTrailerAttachedToVehicle(vehicleid))
  {
  TextDrawHideForPlayer(playerid, weburl);
  } else {
  TextDrawShowForPlayer(playerid, weburl);
  }

  return 1;
}