ROS2-4章：话题（Topic）详细讲解

目录

++[一、Topic（话题）... 2](#一、Topic（话题）... 2)++

++[1.1 创建话题 发布者（Publiser）... 2](#1.1 创建话题 发布者（Publiser）... 2)++

++[1.1.1先进入代码空间... 2](#1.1.1先进入代码空间... 2)++

++[1.1.2创建一个功能包topic_test，以及一个话题发布者publisher 2](#1.1.2创建一个功能包topic_test，以及一个话题发布者publisher 2)++

++[1.1.3打开 vs code. 3](#1.1.3打开 vs code. 3)++

++[1.1.4修改 publisher.py文件内容... 3](#1.1.4修改 publisher.py文件内容... 3)++

++[1.1.5 编译、安装、运行... 4](#1.1.5 编译、安装、运行... 4)++

++[1.2. 创建话题 订阅者（Subscriber）... 5](#1.2. 创建话题 订阅者（Subscriber）... 5)++

++[1.2.1先进入代码空间... 5](#1.2.1先进入代码空间... 5)++

++[1.2.2打开 vs code. 5](#1.2.2打开 vs code. 5)++

++[1.2.3修改 subscriber.py文件内容... 5](#1.2.3修改 subscriber.py文件内容... 5)++

++[1.2.4注册可执行节点... 6](#1.2.4注册可执行节点... 6)++

++[1.2.4 编译、安装... 7](#1.2.4 编译、安装... 7)++

++[1.2.5 运行... 7](#1.2.5 运行... 7)++

一、Topic（话题）

Topic（话题）是 ROS 2 中最基础、最常用的通信方式，它采用发布/订阅（Publish-Subscribe）模型，主要用于节点间异步、单向的数据流传输。

在 ROS 2 中，编写 Topic 通信的代码逻辑非常标准化。无论是 C++ 还是 Python，通常都遵循面向对象编程的思想，核心分为**发布者（Publisher）和订阅者（Subscriber）**两部分。

1. 1. 创建话题 发布者（Publiser）

以下是 Topic 代码逻辑的通用步骤（以 Python 为例，C++ 逻辑完全对称）：创建一个功能包topic_test；包含一个话题发布者节点Publiser；

1.1.1先进入代码空间

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| root@LHAYR:~# cd ~/ros2_ws/src/ root@LHAYR:~/ros2_ws/src# |

1.1.2创建一个功能包topic_test，以及一个话题发布者publisher

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| root@LHAYR:~# cd ~/ros2_ws/src/ root@LHAYR:~/ros2_ws/src# ros2 pkg create --build-type ament_python --node-name publisher --dependencies rclpy std_msgs --license MIT topic_test going to create a new package package name: topic_test destination directory: /root/ros2_ws/src package format: 3 version: 0.0.0 description: TODO: Package description maintainer: 'root \' licenses: 'MIT' build type: ament_python dependencies: 'rclpy', 'std_msgs' node_name: publisher creating folder ./topic_test creating ./topic_test/package.xml creating source folder creating folder ./topic_test/topic_test creating ./topic_test/setup.py creating ./topic_test/setup.cfg creating folder ./topic_test/resource creating ./topic_test/resource/topic_test creating ./topic_test/topic_test/init.py creating folder ./topic_test/test creating ./topic_test/test/test_copyright.py creating ./topic_test/test/test_flake8.py creating ./topic_test/test/test_pep257.py creating ./topic_test/topic_test/publisher.py root@LHAYR:~/ros2_ws/src# 指令中各个参数的详细解析： * ros2 pkg create：这是 ROS 2 中用于创建新软件功能包（Package）的核心命令。 * --build-type ament_python：指定该功能包的构建类型为 Python。ament_python 表示系统会按照 Python 项目的标准（如使用 setup.py）来编译和安装这个包。 * --node-name publisher：这是一个可选参数，用于在创建包时自动生成一个名为 publisher 的节点模板文件（即 publisher.py）。 * --dependencies rclpy std_msgs：声明该功能包运行所需的依赖库。这里指定了 rclpy（ROS 2 的 Python 客户端库）和 std_msgs（标准消息类型库，如字符串、整数等）。 * --license MIT：声明该功能包的开源许可证类型为 MIT。 * topic_test：这是你自定义的功能包名称，必须放在命令的最后。系统会在当前目录下生成一个名为 topic_test 的文件夹。 |

1.1.3打开 vs code

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| root@LHAYR:~/ros2_ws/src# code . root@LHAYR:~/ros2_ws/src# |

1.1.4修改 publisher.py文件内容

修改 publisher.py文件内容（src/topic_test/topic_test/publisher.py）

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| #发布者 import rclpy #倒入rclpy库文件 from rclpy.node import Node # 从 rclpy 中导入 Node 基类，后续自定义节点都要继承它 from std_msgs.msg import String# 导入 ROS 2 内置的标准字符串消息类型，用于定义通信的数据格式 class PubNode(Node): def init(self, node_name='pubnode'): super().init(node_name=node_name) self.pub = self.create_publisher(String, '/hello', 5) # 初始化消息对象 self.msg = String() self.num = 0 # 获取日志记录器 self.logger = self.get_logger() # 创建定时器：每1秒执行一次pubmsg方法 self.create_timer(1.0, self.pubmsg) def pubmsg(self): # 格式化消息内容 self.msg.data = f"the {self.num}th hello message." self.num += 1 # 发布消息 self.pub.publish(self.msg) # 打印日志 self.logger.info(f'send message: {self.msg.data}') def main(args=None): rclpy.init(args=args) node = PubNode() try: rclpy.spin(node) except Exception: # node.destroy_node() rclpy.shutdown() exit(0) if name == 'main': main() |

1.1.5 编译、安装、运行

1. 保存代码，进行编译，安装（跟新环境变量） 和运行

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| root@LHAYR:~/ros2_ws# colcon build --packages-select topic_test --symlink-install Starting >>> topic_test Finished <<< topic_test 0.64s Summary: 1 package finished 0.74s root@LHAYR:~/ros2_ws# # 刷新环境（关键！每次编译后都要做） root@LHAYR:~/ros2_ws# source install/setup.bash #运行程序 root@LHAYR:~/ros2_ws# ros2 run topic_test publisher INFO 1782968817.189284816 pubnode: send message: the 0th hello message. INFO 1782968818.182780941 pubnode: send message: the 1th hello message. INFO 1782968819.182797906 pubnode: send message: the 2th hello message. INFO 1782968820.182748389 pubnode: send message: the 3th hello message. INFO 1782968821.182864452 pubnode: send message: the 4th hello message. |

1. 用指令检测是否发布成功 ros2 topic echo /hello

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| root@LHAYR:~/ros2_ws/src# ros2 topic echo /hello data: the 71th hello message. --- data: the 72th hello message. |

1.2. 创建话题 订阅者（Subscriber）

订阅者（Subscriber）的代码逻辑

订阅者的作用是被动监听特定话题，一旦有新数据到来就自动执行处理逻辑。

1.2.1先进入代码空间

先进入到cd ros2_ws/src/topic_test/topic_test代码空间，新建一个 订阅者文件subsriber.py

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| root@LHAYR:~# cd ros2_ws/src/topic_test/topic_test root@LHAYR:~/ros2_ws/src/topic_test/topic_test# ls init.py pycache publisher.py root@LHAYR:~/ros2_ws/src/topic_test/topic_test# touch subscriber.py root@LHAYR:~/ros2_ws/src/topic_test/topic_test# ls init.py pycache publisher.py subscriber.py root@LHAYR:~/ros2_ws/src/topic_test/topic_test# |

1.2.2打开 vs code

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| root@LHAYR:~/ros2_ws/src# code . root@LHAYR:~/ros2_ws/src# |

1.2.3修改 subscriber.py文件内容

修改 subscriber.py文件内容（src/topic_test/topic_test/subscriber.py）

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| # 订阅者 import rclpy from rclpy.node import Node from std_msgs.msg import String class SubNode(Node): def init(self, node_name='subnode'): super().init(node_name=node_name) # 创建订阅者，监听 /hello 话题，回调函数为 self.process_msg self.sub = self.create_subscription(String, '/hello', self.process_msg, 5) def process_msg(self, msg): # 使用 get_logger() 打印收到的消息 self.get_logger().info(f'receive msg: {msg.data}') def main(args=None): rclpy.init(args=args) node = SubNode() try: rclpy.spin(node) except KeyboardInterrupt: pass finally: # 确保节点资源被正确销毁 node.destroy_node() rclpy.shutdown() if name == 'main': main() |

1.2.4注册可执行节点

在vs code 中打开修改 setup.py文件内容（src/topic_test/setip.py）

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| entry_points={ 'console_scripts': 'publisher = topic_test.publisher:main', 'subscriber = topic_test.subscriber:main', , }, |
| |

1.2.4 编译、安装

保存代码，进行编译，安装（跟新环境变量）

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| r root@LHAYR:~/ros2_ws# colcon build --packages-select topic_test --symlink-install Starting >>> topic_test Finished <<< topic_test 0.58s Summary: 1 package finished 0.64s root@LHAYR:~/ros2_ws# source install/setup.bash |

1.2.5 运行

终端 1重新加载环境，运行发布者：

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| root@LHAYR:~/ros2_ws# cd ~/ros2_ws root@LHAYR:~/ros2_ws# source install/setup.bash root@LHAYR:~/ros2_ws# ros2 run topic_test publisher INFO 1782979604.017530886 pubnode: send message: the 0th hello message. INFO 1782979605.012724652 pubnode: send message: the 1th hello message. |

终端 2重新加载环境，运行订阅者：

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| root@LHAYR:~/ros2_ws# cd ~/ros2_ws root@LHAYR:~/ros2_ws# source install/setup.bash root@LHAYR:~/ros2_ws# ros2 run topic_test subscriber INFO 1782979624.020452777 subnode: receive msg: the 20th hello message. INFO 1782979625.015337360 subnode: receive msg: the 21th hello message. INFO 1782979626.014765692 subnode: receive msg: the 22th hello message. INFO 1782979627.012906893 subnode: receive msg: the 23th hello message. |