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Error on action_client as topic callback

asked 2018-02-13 12:44:37 -0500

bxl gravatar image

updated 2018-02-13 13:38:30 -0500

I'm trying to implement a node that subscribes to a topic to get a list of geometry_msgs/Points and then send it to action_lib client (implemented on the callback function of the subscriber) that communicate to the server.

I'm on ROS Kinetic.

Here are my subscriber:

  rospy.Subscriber(topic_name, topic_type,__goal_action_callback)

And my callback function:

  def __goal_action_callback(data):
    rospy.loginfo(RobotMoving.get_name() + " " + "I heard {}".format(data))
    ac = SimpleActionClient("nav_server", NavigateAction)

    rospy.loginfo("goalCallback: Waiting for action server to start.")

    rospy.loginfo("goalCallback: Navigation service found.")

    goal = NavigateGoal

    goal.target_pos = data


    if ac.get_state() == GoalStatus.SUCCEEDED:
        rospy.loginfo("Navigate action is completed!")
        rospy.loginfo("Navigate action failed!")

Things are working fine for the first point read. However , for the second point and further it gets this error:

[ERROR] [1518537259.290802, 30.718000]: bad callback: <function __goal_action_callback at 0x7fa5d05e5488>
Traceback (most recent call last):
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/rospy/", line 750, in _invoke_callback
  File "/home/bruno/rodain/src/rodain_get_directions/nodes/", line 27, in __goal_action_callback
    ac = SimpleActionClient("nav_server", NavigateAction)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/actionlib/", line 55, in __init__
    self.action_client = ActionClient(ns, ActionSpec)
  File "/opt/ros/kinetic/lib/python2.7/dist-packages/actionlib/", line 519, in __init__
    raise ActionException("Type is not an action spec: %s" % str(ActionSpec))
ActionException: Type is not an action spec: <class 'move_quadcopter.msg._NavigateAction.NavigateAction'>

It seems to me that relys on how things are done on background. Anyone know why it is happening?

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answered 2018-02-13 14:25:53 -0500

gvdhoorn gravatar image

updated 2018-02-13 14:36:16 -0500

ActionException: Type is not an action spec: <class 'move_quadcopter.msg._NavigateAction.NavigateAction'>

It's likely that the following statement in your callback is the problem:

goal = NavigateGoal

You're setting goal equal to the NavigateGoal class, not to an instance of it (ie: an object).

Try changing the line to:

goal = NavigateGoal()

and see whether that works any better.

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the way i've done the subscriber function will get one Point than invoke the callback or it will get all the Points and after i have all call the callback? For me seems it's getting one-by-one but I don't know why.

bxl gravatar image bxl  ( 2018-02-13 17:28:15 -0500 )edit

Your callback will be called for each incoming message, so for N msgs, you will submit N goals to your action server.

gvdhoorn gravatar image gvdhoorn  ( 2018-02-14 01:51:43 -0500 )edit

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Asked: 2018-02-13 12:44:37 -0500

Seen: 2,403 times

Last updated: Feb 13 '18