QGC cannot connect with gazebo simulator

#1

Hello everyone,
I tried the tutorial ‘https://dev.px4.io/en/simulation/ros_interface.html’. QGC could connect with the simulator when i tried ‘make posix_sitl_default gazebo’. But when I tried to use gazebo with ROS wrappers, I did ‘roslaunch px4 posix_sitl.launch’. The simulator can be started, but QGC can not communicate with the simulator. Has anyone meet this problem? How can i do to make QGC communicate with the simulator.
Thank you.