订阅和发布_话题通信探索

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1.话题订阅与发布

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import rclpy
from rclpy.node import Node
import requests
from example_interfaces.msg import String
from queue import Queue

class NovelPubNode(Node):
    def __init__(self,node_name):
        super().__init__(node_name)
        self.get_logger().info(f'{node_name},启动！！！！')
        self.novels_queue=Queue() #创建队列 存数据
        self.novel_publisher_ = self.create_publisher(String,'novel',10)
        self.timer_ = self.create_timer(5,self.timer_callback)#创建定时器

    def timer_callback(self):
        #self.novel_publisher_.publish()
        if self.novels_queue.qsize()>0:#判断队列大小
            line=self.novels_queue.get()
            msg=String()#组装
            msg.data=line
            self.novel_publisher_.publish(msg)
            self.get_logger().info(f'发布了：{msg}')

    def download(self,url):
        response = requests.get(url)
        response.encoding = 'utf-8'
        text = response.text
        self.get_logger().info(f'下载{url},{len(text)}')
        for line in response.text.splitlines():
            self.novels_queue.put(line)#按行分割

def main():
    rclpy.init()
    node = NovelPubNode('novel_pub')
    node.download('http://0.0.0.0:8000/novel1.txt')
    rclpy.spin(node)
    rclpy.shutdown()

ps：

1.执行ros2 run demo_python_topic novel_pub_node时要同时在另一个终端打开服务器python3 -m http.s
erver（这里没注意到当时拖了好几周才解决）

2.ros2 topic echo /novel早于ros2 run demo_python_topic novel_pub_node才能接受到完整的内容

先启动订阅者，再启动发布者（服啦 每次都先启动完发布者，再开订阅者，我说怎么有时候可以收到最后两行。。。）