run a subscriber callback once using rospy.spin()

edit

This: http://answers.ros.org/question/46613/rospy-how-do-you-unsubscribe-to-a-topic-from-within-the-callback/ solution works, at the cost of having to make the subscriber global.

my trick is create spinOnce function by calling it, the callback will be called

def spinOnce(self):
    r = rospy.Rate(self.rate)
    r.sleep()

2 Steps : Flag set to 0 in the class __init__ method. Step 1 : I believe a better alternate is to define the call back method in a class along with the subscriber. And then setting a flag which will be set to one once the callback method has been called for the first time.

Step 2 : Once the Flag has been set 1, in the subscriber declaration block, return to the called block.

An Example is given below : (Tested Works)

class frontCam : def __init__(self): self.flag = 0 rospy.init_node("DFC") self.getVideo()

def getVideo(self) :
    rospy.Rate(1)
    self.image_sub = rospy.Subscriber('Subscribed TOPIC', Message_Type, self.callback )
    print 'Getting Video Feed . . . ' 
    if (self.flag == 1)
        return
    try :
        rospy.spin()
    except KeyboardInterrupt :
        print "Shutting Down"

def callback(self, data) :
    self.flag = 1

However if you guys want, can close the callback method after a certain period using the ropy.sleep() and the return statement as well.

Hi, i tried the given code but my program was stuck on the rospy.spin() procedure after calling the callback for the forst time ! is there a way i can exit from that blocking statement to a next statement ? Thanks