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2 ROS2话题通讯基础(2)

ROS2话题通讯基础

2.5 自定义话题通讯

2.5.1 自定义话题通讯的一般流程

    1. 创建ROS2功能包，功能包可以只用来作为存放自定义的msg/srv，不需要节点node的功能包，且--build-type必须是ament_camke ，因为目前来看，Python的自定义的消息或者服务也需要通过cmake编译出来再调用，功能包必须是下划线的推荐命名方法，而不是大小写的驼峰，否则会报错，如下所示：

2 ROS2话题通讯基础(2)-LMLPHP

--- stderr: msgDemoError                         
CMake Error at /opt/ros/humble/share/rosidl_adapter/cmake/rosidl_adapt_interfaces.cmake:59 (message):
  execute_process(/usr/bin/python3.10 -m rosidl_adapter --package-name
  msgDemoError --arguments-file
  /mnt/hgfs/VMware/ROS2_DEMO/2_Chapter/code/build/msgDemoError/rosidl_adapter__arguments__msgDemoError.json
  --output-dir
  /mnt/hgfs/VMware/ROS2_DEMO/2_Chapter/code/build/msgDemoError/rosidl_adapter/msgDemoError
  --output-file
  /mnt/hgfs/VMware/ROS2_DEMO/2_Chapter/code/build/msgDemoError/rosidl_adapter/msgDemoError.idls)
  returned error code 1:

  Error processing 'String name' of 'msgDemoError/Student': ''msgDemoError'
  is an invalid package name.  It should have the pattern
  '^(?!.*__)(?!.*_$)[a-z][a-z0-9_]*$''

  Traceback (most recent call last):

    File "/usr/lib/python3.10/runpy.py", line 196, in _run_module_as_main
      return _run_code(code, main_globals, None,
    File "/usr/lib/python3.10/runpy.py", line 86, in _run_code
      exec(code, run_globals)
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/__main__.py", line 19, in <module>
      sys.exit(main())
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/main.py", line 53, in main
      abs_idl_file = convert_to_idl(
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/__init__.py", line 19, in convert_to_idl
      return convert_msg_to_idl(
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/msg/__init__.py", line 28, in convert_msg_to_idl
      msg = parse_message_string(package_name, input_file.stem, content)
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/parser.py", line 520, in parse_message_string
      Type(type_string, context_package_name=pkg_name),
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/parser.py", line 277, in __init__
      super(Type, self).__init__(
    File "/opt/ros/humble/local/lib/python3.10/dist-packages/rosidl_adapter/parser.py", line 201, in __init__
      raise InvalidResourceName(

  rosidl_adapter.parser.InvalidResourceName: 'msgDemoError' is an invalid
  package name.  It should have the pattern
  '^(?!.*__)(?!.*_$)[a-z][a-z0-9_]*$'

Call Stack (most recent call first):
  /opt/ros/humble/share/rosidl_cmake/cmake/rosidl_generate_interfaces.cmake:130 (rosidl_adapt_interfaces)
  CMakeLists.txt:16 (rosidl_generate_interfaces)


---
Failed   <<< msgDemoError [1.53s, exited with code 1]
    1. 在ROS2功能包内创建msg文件夹，里面存放自定义的.msg消息文件，并且 .msg文件必须是大写开头的符合类的命名规则
    1. 配置packages.xml文件，都需要配置下面的内容(下面的配置项与.msg文件无关，是默认的固定配置)
<!-- 这一项是针对在msg中可能用到的其他依赖项，例如geomtry_msgs等等，如过没有用到就不添加 -->
<depend>其他的depend</depend>

<!-- 下面三项是必须的 -->
<build_depend>rosidl_default_generators</build_depend>
<exec_depend>rosidl_default_runtime</exec_depend>
<member_of_group>rosidl_interface_packages</member_of_group>
    1. 配置CMakeLists.txt文件,find_package和rosidl_generate_interfaces
# 0. 是针对在msg中可能用到的其他依赖项，例如geomtry_msgs等等，则需要添加
# find_package(geometry_msgs REQUIRED)

# 1. rosidl_default_generators是必须添加的内容
find_package(rosidl_default_generators REQUIRED)

# 2. rosidl_generate_interfaces必须配置，里面添加msg文件位置
rosidl_generate_interfaces(${PROJECT_NAME}
# 2.1 添加自定义的msg位置，例如存放在功能包的msg文件夹下的xxx.msg
  "msg/xxx.msg"
# 2.2 可选，如果xxx.msg依赖了其他的内容,例如依赖了geometry_msgs
  DEPENDENCIES geometry_msgs
)
    1. 编译功能包:colcon build --packages-select <功能包名>
    1. 此时激活install目录下的setup.bash如. install/setup.bash，可以通过ros2 interface show <功能包名称>/msg/xxx.msg查看到xxx.msg内容，此时编译好的msg的.c文件存放在install/<功能包名>/include下，.py文件则存放在install/<功能包名>/local/

2.5.2 创建自定义话题消息简单例子

  1. 创建自定义消息功能包msg_demo，采用ament_cmake方式：ros2 pkg create msg_demo --build-type ament_cmake

  2. 在功能包内创建msg文件夹，其中存放Demo.msg文件，文件内容如下：其中还依赖geometry_msgs

geometry_msgs/Point center
float64 radius
  1. 此时的功能包内部的目录结构如下：tree -a
pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code/msg_demo$ tree -a
.
├── CMakeLists.txt
├── include
│   └── msg_demo
├── msg
│   └── Demo.msg
├── package.xml
└── src

4 directories, 3 files
  1. 配置packages.xml添加依赖项，特别的是该Demo.msg还需依赖gemotry_msgs:
<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
  <name>msg_demo</name>
  <version>0.0.0</version>
  <description>TODO: Package description</description>
  <maintainer email="pldz@R7000.com">pldz</maintainer>
  <license>TODO: License declaration</license>

  <buildtool_depend>ament_cmake</buildtool_depend>

  <!-- 自定义Demo.msg中依赖geometry_msgs所以添加到depend -->
  <depend>geometry_msgs</depend>

  <!-- 构建自定义msg的必须依赖项 -->
  <buildtool_depend>rosidl_default_generators</buildtool_depend>
  <exec_depend>rosidl_default_runtime</exec_depend>
  <member_of_group>rosidl_interface_packages</member_of_group>

  <test_depend>ament_lint_auto</test_depend>
  <test_depend>ament_lint_common</test_depend>

  <export>
    <build_type>ament_cmake</build_type>
  </export>
</package>
  1. 配置CMakeLists.txt文件，添加构建自定义Demo.msg的依赖：
cmake_minimum_required(VERSION 3.8)
project(msg_demo)

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

# find dependencies
find_package(ament_cmake REQUIRED)
# uncomment the following section in order to fill in
# further dependencies manually.
# find_package(<dependency> REQUIRED)

# 1. 自定义的Demo.msg依赖geometry_msgs
find_package(geometry_msgs REQUIRED)
# 2. 必须添加的构建自定义包辅助包的位置
find_package(rosidl_default_generators REQUIRED)

# 3. 构建自定义msg
rosidl_generate_interfaces(${PROJECT_NAME}
  "msg/Demo.msg"                # Demo.msg的位置    
  DEPENDENCIES geometry_msgs    # 创建Demo.msg需要的依赖
)

if(BUILD_TESTING)
  find_package(ament_lint_auto REQUIRED)
  # the following line skips the linter which checks for copyrights
  # comment the line when a copyright and license is added to all source files
  set(ament_cmake_copyright_FOUND TRUE)
  # the following line skips cpplint (only works in a git repo)
  # comment the line when this package is in a git repo and when
  # a copyright and license is added to all source files
  set(ament_cmake_cpplint_FOUND TRUE)
  ament_lint_auto_find_test_dependencies()
endif()

ament_package()

  1. 构建功能包：colcon build --packages-select msg_demo

  2. 查看自定义的消息：激活环境：. install/setup.bash ，查看自定义消息ros2 interface show msg_demo/msg/Demo

pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code$ colcon build --packages-select msg_demo
Starting >>> msg_demo
Finished <<< msg_demo [10.4s]                     

Summary: 1 package finished [10.7s]
pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code$ . install/setup.bash 
pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code$ ros2 interface show msg_demo/msg/Demo 
geometry_msgs/Point center
        float64 x
        float64 y
        float64 z
float64 radius
  1. 查看instll下面的文件：其中.c的class文件在install/<功能包名>/include/<功能包名>/<功能包名>/msg/**，.py在install/<功能包名>/local/lib/python3.10/dist-packages/<功能包名>/msg/**

2 ROS2话题通讯基础(2)-LMLPHP

2.5.3 快速创建C/C++和Python自定义话题通讯的Student.msg

  1. 新建功能包：ros2 pkg create student_msg --build-type ament_cmake

  2. 创建msg文件夹和Student.msg文件，写入如下内容:

string   name
int32    exam
float64  score
  1. 不需要其他依赖项，配置packages.xml添加下面三项即可：
<build_depend>rosidl_default_generators</build_depend>
<exec_depend>rosidl_default_runtime</exec_depend>
<member_of_group>rosidl_interface_packages</member_of_group>
  1. 配置CMakeLists.txt：
find_package(rosidl_default_generators REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "msg/Student.msg"
)
  1. 快速构建：colcon build --packages-select student_msg:
pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code$ colcon build --packages-select student_msg
Starting >>> student_msg
Finished <<< student_msg [8.93s]                     

Summary: 1 package finished [9.21s]

2.6 使用C/C++实现自定义话题通讯

2.6.1 创建C/C++自定义话题发布方功能包并编写节点文件

  1. 创建ROS2功能包,这里为了省的创建node文件直接指定了cpp_idl_pub，指令如下：ros2 pkg create cpp_idl_pub --build-type ament_cmake --node-name cppIdlPubNode，

  2. 配置Vscode：配置Vscode的settings.json：

{
    "C_Cpp.default.includePath": [
        "/opt/ros/humble/include/**",
        "./install/student_msg/include/**"
    ],
    "python.analysis.extraPaths": [
        "/opt/ros/humble/local/lib/python3.10/dist-packages/"
    ],
}
  1. 编写自定义节点文件cppIdlPubNode.cpp：
#include "rclcpp/rclcpp.hpp"

// 1. 添加自定义消息头文件，如果vscode出现下划线警告，则需要配置settings.json添加include路径
#include "student_msg/msg/student.hpp"

// C++14中的时间库
using namespace std::chrono_literals;

// 2. 引入Student.msg生成的Student类
using student_msg::msg::Student;

class CppIdlMsgPub: public rclcpp::Node
{
  public:
      /* 3. ROS2节点的构造函数，其中包括一个node对象（初始化时候没有给出节点的名称），
      * 和属性exam_（初始化为0,类型为size_t)，以及属性socre_（类型为double_t初始值为60.0） */
      CppIdlMsgPub(const char* nodeName):Node(nodeName), exam_(0), score_(60.0)
      {
        // 4. 创建发布者,参数分别为话题名称myStudent，和发布队列的长队为10
        publisher_ = this->create_publisher<Student>("myStudent", 10);
        // 5. 创建定时器，设置发布的频率，并绑定定时执行的事件，这里给到的是CppIdlMsgPub类的函数
        timer_ = this->create_wall_timer(500ms, std::bind(&CppIdlMsgPub::timer_callback, this));
      }

  private:
     // 6. 定义回调函数
    void timer_callback()
    {
      Student stu = Student();
      // 6.1 姓名zhangsan
      stu.name = "zhangsan";
      // 6.2 考试次数递增
      stu.exam = exam_++;
      // 6.3 分数一直递增
      stu.score = score_;
      score_ += 0.1;
      
      RCLCPP_INFO(this->get_logger(), "Student: '%s', exam time: %d, socre is : %f", stu.name.c_str(),stu.exam,stu.score);
      publisher_->publish(stu);

      
    }

    // 5. 计时器、发布者和计数器字段的声明
    rclcpp::TimerBase::SharedPtr timer_;
    rclcpp::Publisher<Student>::SharedPtr publisher_;
    size_t exam_;
    double_t score_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  // 创建节点，给出构造的节点名为CppIdlMsgPubNode
  rclcpp::spin(std::make_shared<CppIdlMsgPub>("CppIdlMsgPubNode"));
  rclcpp::shutdown();
  return 0;
}

2.6.2 配置C/C++自定义话题发布方功能包

  1. 配置packages.xml文件，添加依赖项有rclcpp用于构建节点，和student_msg用于构建Student.msg：
<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
  <name>cpp_idl_pub</name>
  <version>0.0.0</version>
  <description>TODO: Package description</description>
  <maintainer email="pldz@R7000.com">pldz</maintainer>
  <license>TODO: License declaration</license>

  <buildtool_depend>ament_cmake</buildtool_depend>

  <!-- 添加依赖项  -->
  <depend>rclcpp</depend>
  <depend>student_msg</depend>

  <test_depend>ament_lint_auto</test_depend>
  <test_depend>ament_lint_common</test_depend>

  <export>
    <build_type>ament_cmake</build_type>
  </export>
</package>
  1. 配置CMakeLists.txt：
cmake_minimum_required(VERSION 3.8)
project(cpp_idl_pub)

if(CMAKE_COMPILER_IS_GNUCXX OR CMAKE_CXX_COMPILER_ID MATCHES "Clang")
  add_compile_options(-Wall -Wextra -Wpedantic)
endif()

# find dependencies
find_package(ament_cmake REQUIRED)

# 1. 添加依赖项
find_package(rclcpp REQUIRED)
find_package(student_msg REQUIRED)
# uncomment the following section in order to fill in
# further dependencies manually.
# find_package(<dependency> REQUIRED)

# 2. 默认是已经创建了构建节点的文件配置
add_executable(cppIdlPubNode src/cppIdlPubNode.cpp)

# 3. 默认已经包括<INSTALL_INTERFACE>的路径也不用更改
target_include_directories(cppIdlPubNode PUBLIC
  $<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
  $<INSTALL_INTERFACE:include>)


# 4. ament工具构建节点的依赖配置
ament_target_dependencies(
  cppIdlPubNode
  rclcpp
  student_msg
)

target_compile_features(cppIdlPubNode PUBLIC c_std_99 cxx_std_17)  # Require C99 and C++17

# 5. Install配置，默认ros2 run <包名>的配置
install(TARGETS cppIdlPubNode
  DESTINATION lib/${PROJECT_NAME})

if(BUILD_TESTING)
  find_package(ament_lint_auto REQUIRED)
  # the following line skips the linter which checks for copyrights
  # comment the line when a copyright and license is added to all source files
  set(ament_cmake_copyright_FOUND TRUE)
  # the following line skips cpplint (only works in a git repo)
  # comment the line when this package is in a git repo and when
  # a copyright and license is added to all source files
  set(ament_cmake_cpplint_FOUND TRUE)
  ament_lint_auto_find_test_dependencies()
endif()

# 6. 生成包的环境
ament_package()

2.6.3 编译并运行C/C++自定义话题发布方功能包

  1. 编译： colcon build --packages-select cpp_idl_pub

  2. 激活环境：. install/setup.bash

  3. 运行：ros2 run cpp_idl_pub cppIdlPubNode

pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code$ colcon build --packages-select cpp_idl_pub
Starting >>> cpp_idl_pub
Finished <<< cpp_idl_pub [10.0s]                     

Summary: 1 package finished [10.4s]
pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code$ . install/setup.bash
pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code$ ros2 run cpp_idl_pub cppIdlPubNode 
[INFO] [1683041064.126034476] [CppIdlMsgPubNode]: Student: 'zhangsan', exam time: 0, socre is : 60.000000
[INFO] [1683041064.625514370] [CppIdlMsgPubNode]: Student: 'zhangsan', exam time: 1, socre is : 60.100000
[INFO] [1683041065.125571561] [CppIdlMsgPubNode]: Student: 'zhangsan', exam time: 2, socre is : 60.200000
^C[INFO] [1683041082.271152379] [rclcpp]: signal_handler(signum=2)

2.6.4 创建C/C++自定义话题订阅方功能包并编辑节点文件

  1. 创建ROS2功能包，包名为cpp_idl_sub，节点名称为cppIdlSubNode，并直接指定依赖项为rclcpp和student_msg，如下所示：ros2 pkg create cpp_idl_sub --build-type ament_cmake --node-name cppIdlSubNode --dependencies rclcpp student_msg

  2. 编辑节点文件：订阅Student类型的话题，话题名为myStudent:

#include "rclcpp/rclcpp.hpp"

// 1. 添加自定义消息头文件，如果vscode出现下划线警告，则需要配置settings.json添加include路径
#include "student_msg/msg/student.hpp"

// 占位符，结合std::bind函数的绑定使用
using std::placeholders::_1;

// 2. 引入Student.msg生成的Student类
using student_msg::msg::Student;

class CppIdlMsgSub: public rclcpp::Node
{
  public:
      /* 3. ROS2节点的构造函数，其中包括一个node对象（初始化时候没有给出节点的名称），
      * 和属性exam_（初始化为0,类型为size_t)，以及属性socre_（类型为double_t初始值为60.0） */
      CppIdlMsgSub(const char* nodeName):Node(nodeName)
      {
      subscription_ = this->create_subscription<Student>(
      "myStudent", 10, std::bind(&CppIdlMsgSub::topic_callback, this, _1));
      }

  private:
    // 4. 定义订阅到消息的回调函数
    void topic_callback(const Student & stu) const
    {
      RCLCPP_INFO(this->get_logger(), "I heard: %s, exam: %d, score: %f", stu.name.c_str(),stu.exam, stu.score);
    }

    // 5. 计时器、发布者和计数器字段的声明
    rclcpp::Subscription<Student>::SharedPtr subscription_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  // 创建节点，给出构造的节点名为CppIdlMsgSubNode
  rclcpp::spin(std::make_shared<CppIdlMsgSub>("CppIdlMsgSubNode"));
  rclcpp::shutdown();
  return 0;
}

2.6.5 编译并运行C/C++自定义话题订阅节点

  1. 由于在创建包时候已经指定了依赖项，可以不用再进行配置packages.xml和CMakeLists.txt文件，直接编译colcon build --packages-select cpp_idl_sub

  2. 激活环境：. install/setup.bash

  3. 运行：
    2 ROS2话题通讯基础(2)-LMLPHP

2.7 使用Python实现自定义话题通讯

2.7.1 创建Python自定义话题订阅方节点并编写节点内容

  1. 创建ROS2 Python发布方功能包，包名为python_idl_pub,节点名为pythonIdlPubNode：ros2 pkg create python_idl_pub --build-type ament_python --node-name pythonIdlPubNode

  2. 配置Vscode环境：在settings.json中添加Python的依赖项位置，虽然编译不影响报错，但是vscode的警告看着也不习惯：

2 ROS2话题通讯基础(2)-LMLPHP

  1. 编写订阅节点：
import rclpy
from rclpy.node import Node

# 1. 导入包，如果vscode下划线警告，则需要配置settings.json
from student_msg.msg import Student


class PythonIdlPub(Node):

    def __init__(self, nodeName):
        # 1. 初始化父类构造函数，其中节点名需要创建时候指定
        super().__init__(nodeName)
        self.exam_ = 0
        self.score_ = 60.0
        # 2. 声明发布者，发布消息类型为Student，话题名为myStudent,队列大小为10
        self.publisher_ = self.create_publisher(Student, 'myStudent', 10)
        # 3. 创建定时器，其中更新频率为0.5秒，并绑定回调函数
        self.timer = self.create_timer(0.5, self.timer_callback)
        
    # 4. 定义回调函数
    def timer_callback(self):
        stu = Student()
        stu.name = "zhangsan"
        stu.exam = self.exam_
        stu.score = self.score_

        self.publisher_.publish(stu)
        self.get_logger().info('Publishing: name: {}, exam:{}, score:{}'.format(stu.name,stu.exam,stu.score))
        self.exam_ += 1
        self.score_ += 0.1


def main(args=None):
    rclpy.init(args=args)
    pythonIdlPubNode = PythonIdlPub("pythonIdlPubNode")
    rclpy.spin(pythonIdlPubNode)
    # 销毁节点
    pythonIdlPubNode.destroy_node()
    rclpy.shutdown()


if __name__ == '__main__':
    main()

2.7.2 配置Python自定义订阅方功能包

  1. 配置packages.xml增加rclpy和student_msg两个依赖项，注意Python本身是可执行文件，因此它的为<exec_depend>与C/C++的<depend>关键字不同：
<?xml version="1.0"?>
<?xml-model href="http://download.ros.org/schema/package_format3.xsd" schematypens="http://www.w3.org/2001/XMLSchema"?>
<package format="3">
  <name>python_idl_pub</name>
  <version>0.0.0</version>
  <description>TODO: Package description</description>
  <maintainer email="pldz@R7000.com">pldz</maintainer>
  <license>TODO: License declaration</license>

  <test_depend>ament_copyright</test_depend>
  <test_depend>ament_flake8</test_depend>
  <test_depend>ament_pep257</test_depend>
  <test_depend>python3-pytest</test_depend>

  <!-- 添加依赖项 -->
  <exec_depend>rclpy</exec_depend>
  <exec_depend>student_msg</exec_depend>

  <export>
    <build_type>ament_python</build_type>
  </export>
</package>
  1. 配置setup.py文件，事实上，我们已经创建包的时候已经指定了节点名，其实应该是不用配置生成节点的main入口的：
from setuptools import setup

package_name = 'python_idl_pub'

setup(
    name=package_name,
    version='0.0.0',
    packages=[package_name],
    data_files=[
        ('share/ament_index/resource_index/packages',
            ['resource/' + package_name]),
        ('share/' + package_name, ['package.xml']),
    ],
    install_requires=['setuptools'],
    zip_safe=True,
    maintainer='pldz',
    maintainer_email='pldz@R7000.com',
    description='TODO: Package description',
    license='TODO: License declaration',
    tests_require=['pytest'],
    # 配置节点的main函数入口
    entry_points={
        'console_scripts': [
            'pythonIdlPubNode = python_idl_pub.pythonIdlPubNode:main'
        ],
    },
)

2.7.3 编译并运行Python自定义话题发布方

  1. 编译：colcon build --packages-select python_idl_pub

  2. 激活环境：. install/setup.bash

  3. 运行节点：ros2 run python_idl_pub pythonIdlPubNode

pldz@pldz-pc:~/share/ROS2_DEMO/2_Chapter/code$ ros2 run python_idl_pub pythonIdlPubNode 
[INFO] [1683044269.902750751] [pythonIdlPubNode]: Publishing: name: zhangsan, exam:0, score:60.0
[INFO] [1683044270.393748471] [pythonIdlPubNode]: Publishing: name: zhangsan, exam:1, score:60.1
[INFO] [1683044270.891683074] [pythonIdlPubNode]: Publishing: name: zhangsan, exam:2, score:60.2

2.7.4 创建Python自定义话题订阅方

  1. 创建Python功能包时，包名为python_idl_sub，节点名为pythonIdlSubNode，直接指定依赖项rclpy和student_msg：ros2 pkg create python_idl_sub --build-type ament_python --node-name pythonIdlSubNode --dependencies rclpy student_msg

  2. 编写节点：

import rclpy
from rclpy.node import Node

# 1. 导入包，如果vscode下划线警告，则需要配置settings.json
from student_msg.msg import Student


class PythonIdlSub(Node):

    def __init__(self, nodeName):
        # 1. 构造函数，初始化node节点
        super().__init__(nodeName)
        # 2. 声明订阅者，订阅话题`myTopicNmae`,并绑定回调函数
        self.subscription = self.create_subscription(Student,'myStudent',self.listener_callback,10)

    # 3. 定义回调函数
    def listener_callback(self, stu:Student):
        self.get_logger().info('I heard: name:{}, exam:{}, score{}'.format(stu.name, stu.exam, stu.score))


def main(args=None):
    rclpy.init(args=args)
    pythonIdlSubNode = PythonIdlSub("pythonIdlSubNode")
    rclpy.spin(pythonIdlSubNode)
    pythonIdlSubNode.destroy_node()
    rclpy.shutdown()

if __name__ == '__main__':
    main()

2.7.5 编译运行Python发布方节点

  1. 由于指定了依赖项，直接编译即可: colcon build --packages-select python_idl_sub

  2. 激活环境: . install/setup.bash

  3. 运行所有节点：

2 ROS2话题通讯基础(2)-LMLPHP

2.8 话题通讯小结

    1. 创建功能包时，如果能够直接指定节点名和依赖项，可以省去很大部分的配置工作
    1. C/C++手动配置功能包时，packages.xml配置依赖项，CMakeLists.txt配置编译的内容，包括find_package；add_executable；target_include_directories；ament_target_dependencies；install；ament_package这六个部分
    1. Python手动配置功能包时，packages.xml配置可执行的依赖项exec_depend而不是depend,并且在setup.py中主要配置节点的main函数入口
    1. 自定义话题通讯，本质是创建一个C/C++的功能包，将里面的自定义消息编译成可以使用的.c和.py文件，值得注意的是，生成好的中间文件是存放在 工作空间的install文件夹下，如果这个这个工作空间的install找不到或者不是一个，那是需要再进一步的手动配置的
05-04 10:39
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