ROS的动作非常适合时间不确定，目标导向型的操作接口。原理上用话题实现，其本质是相关于规定了一系列话题（目标、结果、反馈、取消等）的组合使用方法的高层协议。
1、定义动作 与 相关话题说明
选中action目录名，右键AddActionFile,这里定义类似定时器的动作，格式与service类似，分为goal、result、feedback三段，同样由‘---’分隔，文件Timer.action内容：
#the goal
duration time_to_wait # Specify which dishwasher we want to use
---
#the result
duration timer_elapsed
int32 updates_sent
---
# the feedback message
duration timer_elapsed
duration timer_remaining为了帮助理解，我这里先把动作有关的测试结果展示出来，添加并启动动作服务端simple_action_server与客户端程序simple_action_client（后文有详细介绍）以后，新出现了timer动作的五个话题：
wsc@wsc-pc:~/ros1_ws$ rostopic list
/rosout
/rosout_agg
/timer/cancel
/timer/feedback
/timer/goal
/timer/result
其中goal、cancer消息 ，由client端发布，server端订阅，而result、feedback消息 ，由server端发布，client端订阅，话题的详细信息如下：
wsc@wsc-pc:~/ros1_ws$ rostopic info /timer/goal
Type: ros_dev_test/TimerActionGoal
Publishers:
* /simple_action_client (http://wsc-pc:35747/)
Subscribers:
* /simple_action_server (http://wsc-pc:41467/)
wsc@wsc-pc:~/ros1_ws$ rostopic info /timer/result
Type: ros_dev_test/TimerActionResult
Publishers:
* /simple_action_server (http://wsc-pc:41467/)
Subscribers:
* /simple_action_client (http://wsc-pc:34939/)
wsc@wsc-pc:~/ros1_ws$ rostopic info /timer/feedback
Type: ros_dev_test/TimerActionFeedback
Publishers:
* /simple_action_server (http://wsc-pc:41467/)
Subscribers:
* /simple_action_client (http://wsc-pc:42565/)
wsc@wsc-pc:~/ros1_ws$ rostopic info /timer/cancel
Type: actionlib_msgs/GoalID
Publishers:
* /simple_action_client (http://wsc-pc:40621/)
Subscribers:
* /simple_action_server (http://wsc-pc:41467/)以/timer/goal为例，其消息类型为TimerActionGoal，我们来看看其详细信息：
wsc@wsc-pc:~/ros1_ws$ rosmsg show TimerActionGoal
[ros_dev_test/TimerActionGoal]:
std_msgs/Header header
uint32 seq
time stamp
string frame_id
actionlib_msgs/GoalID goal_id
time stamp
string id
ros_dev_test/TimerGoal goal
duration time_to_wait可以看出其是一个组合消息，其中与我们自己定义相关的是ros_dev_test/TimerGoal，其详细信息如下：
wsc@wsc-pc:~/ros1_ws$ rosmsg show TimerGoal
[ros_dev_test/TimerGoal]:
duration time_to_wait
可以看出这个是和action文件的goal段对应可以来的，另外还有：
wsc@wsc-pc:~/ros1_ws$ rosmsg show TimerResult
[ros_dev_test/TimerResult]:
duration timer_elapsed
int32 updates_sent
wsc@wsc-pc:~/ros1_ws$ rosmsg show TimerFeedback
[ros_dev_test/TimerFeedback]:
duration timer_elapsed
duration timer_remaining以上的 TimerAction、TimerActionGoal、TimerActionFeedback、TimerActionResult、TimerGoal、TimerFeedback、TimerResult在加入action动作文件后由ROS编译系统自动生成，同样，添加action文件需要对CMakeLists.txt、package.xml 进行的修改RoboWare Studio也替我们自动完成了，CMakeLists.txt主要修改了以下几处：
2、实现动作server端
代码及注释如下：
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import rospy
import time
#actionlib包含了了SimpleActionServer
import actionlib
# 导入action文件自动生成的消息类
from ros_dev_test.msg import TimerAction,TimerGoal,TimerResult
#goal处理函数并返回处理结果
def do_timer(goal):
start_time=time.time()
time.sleep(goal.time_to_wait.to_sec())
result=TimerResult()
result.timer_elapsed=rospy.Duration.from_sec(time.time()-start_time)
result.updates_sent=0
action_server.set_succeeded(result)
rospy.init_node('simple_action_server')
action_server=actionlib.SimpleActionServer('timer',TimerAction,do_timer,False)
action_server.start()
rospy.spin()注意运行前先要通过chmod u+x 命令添加运行权限。
3、client端使用动作
使用服务的client端代码及注释如下：
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import rospy
import time
#actionlib包含了了SimpleActionServer
import actionlib
# 导入action文件自动生成的消息类
from ros_dev_test.msg import TimerAction,TimerGoal,TimerResult
rospy.init_node('simple_action_client')
action_client=actionlib.SimpleActionClient('timer',TimerAction)
#等待服务启动
action_client.wait_for_server()
#发送goal消息
goal=TimerGoal()
goal.time_to_wait=rospy.Duration.from_sec(5.0)
action_client.send_goal(goal)
action_client.wait_for_result()
print('Time elapsed: %f' %(action_client.get_result().timer_elapsed.to_sec()))注意运行前先要通过chmod u+x 命令添加运行权限。
3、完整一点的server端与client端代码
#!/usr/bin/env python
# -*- coding: utf-8 -*-
import rospy
import time
#actionlib包含了了SimpleActionServer
import actionlib
# 导入action文件自动生成的消息类
from ros_dev_test.msg import TimerAction,TimerGoal,TimerResult,TimerFeedback
#goal处理函数并返回处理结果
def do_timer(goal):
start_time=time.time()
update_count=0
#异常处理
if goal.time_to_wait.to_sec()>60.0:
result=TimerResult()
result.timer_elapsed=rospy.Duration.from_sec(time.time()-start_time)
result.updates_sent=update_count
#动作异常退出
action_server.set_aborted(result,'Timer aborted due to too-long wait')
return
while((time.time()-start_time)<goal.time_to_wait.to_sec()):
#判断是否发生中断，比如收到新的目标或者客户端取消目标等
if action_server.is_preempt_requested():
result=TimerResult()
result.timer_elapsed=rospy.Duration.from_sec(time.time()-start_time)
result.updates_sent=update_count
action_server.set_preempted(result,'Timer preempted')
return
feedback=TimerFeedback()
feedback.timer_elapsed=rospy.Duration.from_sec(time.time()-start_time)
feedback.timer_remaining=goal.time_to_wait-feedback.timer_elapsed
action_server.publish_feedback(feedback)
update_count+=1
time.sleep(1)
result=TimerResult()
result.timer_elapsed=rospy.Duration.from_sec(time.time()-start_time)
result.updates_sent=update_count
action_server.set_succeeded(result,'Timer completed successfully')
rospy.init_node('simple_action_server')
action_server=actionlib.SimpleActionServer('timer',TimerAction,do_timer,False)
action_server.start()
print 'start server'
rospy.spin()#!/usr/bin/env python
# -*- coding: utf-8 -*-
import rospy
import time
#actionlib包含了了SimpleActionServer
import actionlib
# 导入action文件自动生成的消息类
from ros_dev_test.msg import TimerAction,TimerGoal,TimerResult,TimerFeedback
def feedback_callback(feedback):
print('[feedback] timer_elapsed %f'% (feedback.timer_elapsed.to_sec()))
print('[feedback] timer_remaining %f'% (feedback.timer_remaining.to_sec()))
rospy.init_node('simple_action_client')
action_client=actionlib.SimpleActionClient('timer',TimerAction)
#等待服务启动
action_client.wait_for_server()
#发送goal消息
goal=TimerGoal()
goal.time_to_wait=rospy.Duration.from_sec(5.0)
action_client.send_goal(goal,feedback_cb=feedback_callback)
#测试时间超长异常
# goal.time_to_wait=rospy.Duration.from_sec(70.0)
# action_client.send_goal(goal)
#测试中途取消终止目标
# time.sleep(3.0)
# action_client.cancel_goal()
action_client.wait_for_result()
print('[Result] state: %d' %(action_client.get_state()))
print('[Result] status: %s' %(action_client.get_goal_status_text()))
print('[Result] Updates_sent: %f' %(action_client.get_result().updates_sent))
print('[Result] Time elapsed: %f' %(action_client.get_result().timer_elapsed.to_sec()))