1. 自定义topic消息

1.1 创建package

ros2 pkg create --build-type ament_cmake msg_srv

可以修改package.xml文件如下信息

<description>C++ client server tutorial</description>
<maintainer email="you@email.com">Your Name</maintainer>
<license>Apache License 2.0</license>

1.2 在工程下创建msg文件夹,创建Num.msg文件并填写如下内容

int64 num

1.3 配置cmake

find_package(rosidl_default_generators REQUIRED)
rosidl_generate_interfaces(${PROJECT_NAME}
  "msg/Num.msg"
)

出现如下问题
Could NOT find OpenSSL, try to set the path to OpenSSL root folder in the system variable OPENSSL_ROOT_DIR (missing: OPENSSL_LIBRARIES OPENSSL_INCLUDE_DIR)
执行如下命令即可

sudo apt-get install libssl-dev

1.4 配置package.xml文件

<build_depend>rosidl_default_generators</build_depend>
<exec_depend>rosidl_default_runtime</exec_depend>
<member_of_group>rosidl_interface_packages</member_of_group>

1.5 编译工程

colcon build --packages-select msg_srv

1.6 显示消息详情

ros2 interface show msg_srv/msg/Num

2. 使用自定义的topic消息

2.1 publisher

import rclpy
from rclpy.node import Node
from msg_srv.msg import Num
class MyNode(Node):
    def __init__(self):
        super(MyNode, self).__init__('publisher_py')
        self.publisher = self.create_publisher(Num, 'py_topic', 10)
        timer_period = 0.5  # seconds
        self.timer = self.create_timer(timer_period, self.timer_callback)
        self.i = 0
    def timer_callback(self):
        msg = Num()
        msg.num = self.i
        self.publisher.publish(msg)
        self.get_logger().info('Publishing: "%d"' % msg.num)
        self.i += 1
def main():
    rclpy.init()
    node = MyNode()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()
if __name__ == '__main__':
    main()

2.2 subscriber

import rclpy
from rclpy.node import Node
from msg_srv.msg import Num
class MyNode(Node):
    def __init__(self):
        super(MyNode, self).__init__('subscriber_node')
        self.subscription = self.create_subscription(Num, 'py_topic', self.msg_call_back, 10)
    def msg_call_back(self, msg):
        self.get_logger().info(f'msg:{msg.num}')
def main():
    rclpy.init()
    node = MyNode()
    rclpy.spin(node)
    node.destroy_node()
    rclpy.shutdown()
if __name__ == '__main__':
    main()

2.3 package.xml配置

<exec_depend>msg_srv</exec_depend>

2.4 setup.py配置

entry_points={
    'console_scripts': [
        ...
        'publisher_msg = py_pubsub.publisher_msg:main',
        'subscriber_msg = py_pubsub.subscriber_msg:main',
    ],
},

2.5 编译工程

colcon build

2.6 运行节点

ros2 run py_pubsub publisher_msg 
ros2 run py_pubsub subscriber_msg