ROS与Python入门教程-actionlib-开发简单的action客户端

ROS与Python入门教程-actionlib-开发简单的action客户端

说明

• 使用SimpleActionClient库创建Python的Fibonacci(斐波那契数列)action客户端
• 发送目标并获取反馈结果

介绍

• 了解actionlib，查看actionlib_tutorials
• 访问代码库
• actionlib_tutorials/simple_action_client/fibonacci_client.py

代码

#! /usr/bin/env python

import roslib; roslib.load_manifest('actionlib_tutorials')
import rospy

# Brings in the SimpleActionClient
import actionlib

# Brings in the messages used by the fibonacci action, including the
# goal message and the result message.
import actionlib_tutorials.msg

def fibonacci_client():
    # Creates the SimpleActionClient, passing the type of the action
    # (FibonacciAction) to the constructor.
    client = actionlib.SimpleActionClient('fibonacci', actionlib_tutorials.msg.FibonacciAction)

    # Waits until the action server has started up and started
    # listening for goals.
    client.wait_for_server()

    # Creates a goal to send to the action server.
    goal = actionlib_tutorials.msg.FibonacciGoal(order=20)

    # Sends the goal to the action server.
    client.send_goal(goal)

    # Waits for the server to finish performing the action.
    client.wait_for_result()

    # Prints out the result of executing the action
    return client.get_result()  # A FibonacciResult

if __name__ == '__main__':
    try:
        # Initializes a rospy node so that the SimpleActionClient can
        # publish and subscribe over ROS.
        rospy.init_node('fibonacci_client_py')
        result = fibonacci_client()
        print "Result:", ', '.join([str(n) for n in result.sequence])
    except rospy.ROSInterruptException:
        print "program interrupted before completion"

代码分析：

• 代码：import actionlib_tutorials.msg

• 分析：导入生成的消息，action会生成用于发送目标，接受反馈的消息。

• 代码：client = actionlib.SimpleActionClient('fibonacci', actionlib_tutorials.msg.FibonacciAction)

• 分析：创建action客户端，action客户端和action服务器端利用一系列主题(在actionlib协议描述)交流。action名称描述了包含这些主题的命名空间，并且action规范消息描述了这些主题应该传递什么信息。

• 代码：client.wait_for_server()

• 分析：在action服务器端运行之前发送目标是无效的，这行就等待直到action服务器端连接上。

• 代码：

# Creates a goal to send to the action server.
goal = actionlib_tutorials.msg.FibonacciGoal(order=20)

# Sends the goal to the action server.
client.send_goal(goal)

• 分析：创建目标并发送到action服务器端

• 代码：

# Waits for the server to finish performing the action.
client.wait_for_result()

# Prints out the result of executing the action
return client.get_result()  # A FibonacciResult

• 分析：等待action服务器端完成运算，并取得反馈的结果。

运行客户端

• 运行roscore

$ roscore

• 运行服务器端

$ rosrun actionlib_tutorials fibonacci_server

• 运行客户端

$ rosrun actionlib_tutorials fibonacci_client.py