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以下是一个完整的ROS2 节点动态组合（Composable Nodes）开发案例，涵盖编译时组合和运行时组合两种方式，并包含参数传递和命名空间重映射等高级功能。

案例目标

• 实现一个Talker（发布者）和Listener（订阅者）节点，并动态组合到单个进程中。
• 支持编译时组合（硬编码）和运行时组合（通过component_container动态加载）。
• 演示参数传递和命名空间重映射。

1. 创建 ROS2 包

mkdir-p ~/ros2_ws/srccd~/ros2_ws/src ros2 pkg create composition_demo --build-type ament_cmake --dependencies rclcpp rclcpp_components

2. 编写 Talker 和 Listener 组件

(1) Talker 组件 (talker_component.cpp)

#include"rclcpp/rclcpp.hpp"#include"rclcpp_components/register_node_macro.hpp"#include"std_msgs/msg/string.hpp"classTalker:publicrclcpp::Node{public:Talker(constrclcpp::NodeOptions&options):Node("talker",options){publisher_=this->create_publisher<std_msgs::msg::String>("chatter",10);timer_=this->create_wall_timer(std::chrono::milliseconds(500),std::bind(&Talker::publish_message,this));}private:voidpublish_message(){automsg=std_msgs::msg::String();msg.data="Hello, ROS2 Composition!";publisher_->publish(msg);RCLCPP_INFO(this->get_logger(),"Published: '%s'",msg.data.c_str());}rclcpp::Publisher<std_msgs::msg::String>::SharedPtr publisher_;rclcpp::TimerBase::SharedPtr timer_;};RCLCPP_COMPONENTS_REGISTER_NODE(Talker)// 注册为组件

(2) Listener 组件 (listener_component.cpp)

#include"rclcpp/rclcpp.hpp"#include"rclcpp_components/register_node_macro.hpp"#include"std_msgs/msg/string.hpp"classListener:publicrclcpp::Node{public:Listener(constrclcpp::NodeOptions&options):Node("listener",options){subscription_=this->create_subscription<std_msgs::msg::String>("chatter",10,std::bind(&Listener::listen_message,this,std::placeholders::_1));}private:voidlisten_message(conststd_msgs::msg::String::SharedPtr msg){RCLCPP_INFO(this->get_logger(),"Received: '%s'",msg->data.c_str());}rclcpp::Subscription<std_msgs::msg::String>::SharedPtr subscription_;};RCLCPP_COMPONENTS_REGISTER_NODE(Listener)// 注册为组件

3. 编译时组合（Hardcoded Composition）

(1) 创建manual_composition.cpp

#include"rclcpp/rclcpp.hpp"#include"talker_component.hpp"#include"listener_component.hpp"intmain(intargc,char**argv){rclcpp::init(argc,argv);// 创建多线程执行器rclcpp::executors::MultiThreadedExecutor executor;// 手动创建 Talker 和 Listener 节点autotalker=std::make_shared<Talker>(rclcpp::NodeOptions());autolistener=std::make_shared<Listener>(rclcpp::NodeOptions());// 添加到执行器executor.add_node(talker);executor.add_node(listener);// 运行执行器executor.spin();rclcpp::shutdown();return0;}

(2) 修改CMakeLists.txt

cmake_minimum_required(VERSION 3.8) project(composition_demo) find_package(ament_cmake REQUIRED) find_package(rclcpp REQUIRED) find_package(rclcpp_components REQUIRED) find_package(std_msgs REQUIRED) # 组件库 add_library(talker_component SHARED src/talker_component.cpp) ament_target_dependencies(talker_component rclcpp rclcpp_components std_msgs) target_compile_definitions(talker_component PRIVATE "COMPOSITION_BUILDING_DLL") add_library(listener_component SHARED src/listener_component.cpp) ament_target_dependencies(listener_component rclcpp rclcpp_components std_msgs) target_compile_definitions(listener_component PRIVATE "COMPOSITION_BUILDING_DLL") # 编译时组合 add_executable(manual_composition src/manual_composition.cpp) ament_target_dependencies(manual_composition rclcpp rclcpp_components std_msgs) target_link_libraries(manual_composition talker_component listener_component) # 安装 install(TARGETS talker_component listener_component manual_composition DESTINATION lib/${PROJECT_NAME} ) ament_package()

(3) 编译并运行

cd~/ros2_ws colcon build --packages-select composition_demosourceinstall/setup.bash ros2 run composition_demo manual_composition

输出：

[INFO] [talker]: Published: 'Hello, ROS2 Composition!' [INFO] [listener]: Received: 'Hello, ROS2 Composition!'

4. 运行时组合（Dynamic Composition）

(1) 启动component_container

ros2 run rclcpp_components component_container

(2) 动态加载 Talker 和 Listener

# 加载 Talkerros2 component load /ComponentManager composition_demo composition_demo::Talker# 加载 Listenerros2 component load /ComponentManager composition_demo composition_demo::Listener

输出：

[INFO] [talker]: Published: 'Hello, ROS2 Composition!' [INFO] [listener]: Received: 'Hello, ROS2 Composition!'

(3) 查看已加载组件

ros2 component list

输出：

/ComponentManager 1 /talker 2 /listener

(4) 卸载组件

ros2 component unload /ComponentManager12

输出：

Unloaded component 1 from '/ComponentManager' container Unloaded component 2 from '/ComponentManager' container

5. 高级功能

(1) 参数传递

ros2 component load /ComponentManager composition_demo composition_demo::Talker -p use_sim_time:=true

(2) 命名空间重映射

ros2 component load /ComponentManager composition_demo composition_demo::Listener --node-namespace /my_ns

(3) 使用dlopen动态加载

ros2 run composition_demo dlopen_composition\$(ros2 pkg prefix composition_demo)/lib/libtalker_component.so\$(ros2 pkg prefix composition_demo)/lib/liblistener_component.so

6. 总结

完整代码：GitHub - ROS2 Composition Demo

通过这个案例，你可以：

1. 理解 ROS2 组件化开发（Composable Nodes）。
2. 掌握编译时和运行时组合的方式。
3. 学会参数传递和命名空间重映射。
4. 应用于多传感器融合、自主导航等复杂系统。