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1. 查看自定义消息

引用在《ROS2 入门应用 创建自定义接口》中自定义的消息Sphere.msg

ros2 interface show tutorial_interfaces/msg/Sphere# geometry_msgs/Point center
#         float64 x
#         float64 y
#         float64 z
# float64 radius

需要对《ROS2 入门应用 发布和订阅（C++）》中创建的发布者/订阅者功能包稍作修改

cd ~/ros2_ws/src/cpp_pubsub/src

将把数值的字符串更改为球体半径

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2. 修改话题发布

修改publisher_member_function.cpp话题发布源文件，涉及话题类型变更和应用变化

#include <chrono>
#include <memory>#include "rclcpp/rclcpp.hpp"
#include "tutorial_interfaces/msg/sphere.hpp"  // CHANGE/* 方便表示时间 */
using namespace std::chrono_literals;/* 继承rclcpp:: node创建节点类MinimalPublisher */
class MinimalPublisher : public rclcpp::Node
{public:/* 公共构造函数将节点命名为minimal_publisher，并将count_初始化为0 */MinimalPublisher(): Node("minimal_publisher"), count_(0){/* 初始化发布者publisher_ ，使用Sphere消息类型、主题名称topic和在发生备份时限制消息所需的队列大小10 */publisher_ = this->create_publisher<tutorial_interfaces::msg::Sphere>("topic", 10);  // CHANGE/* 初始化timer_，设置timer_callback函数每500ms执行一次 */timer_ = this->create_wall_timer(500ms, std::bind(&MinimalPublisher::timer_callback, this));}private:/* 定义定时器回调函数 */void timer_callback(){/* 打印并发布球体半径信息 */auto message = tutorial_interfaces::msg::Sphere();                                 // CHANGEmessage.radius = this->count_++;                                                   // CHANGERCLCPP_INFO_STREAM(this->get_logger(), "Publishing: '" << message.radius << "'");  // CHANGEpublisher_->publish(message);}/* 计时器、发布者和计数器字段的声明 */rclcpp::TimerBase::SharedPtr timer_;rclcpp::Publisher<tutorial_interfaces::msg::Sphere>::SharedPtr publisher_;  // CHANGEsize_t count_;
};int main(int argc, char * argv[])
{/* 初始化ROS2 */rclcpp::init(argc, argv);/* 运行节点MinimalPublisher */rclcpp::spin(std::make_shared<MinimalPublisher>());/* 退出ROS2 */rclcpp::shutdown();return 0;
}

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3. 修改话题订阅

修改subscriber_member_function.cpp话题订阅源文件，涉及话题类型变更和应用变化

#include <memory>#include "rclcpp/rclcpp.hpp"
#include "tutorial_interfaces/msg/sphere.hpp"  // CHANGE/* 占位符，代替回调函数中的第一个参数 */
using std::placeholders::_1;/* 继承rclcpp:: node创建节点类MinimalSubscriber */
class MinimalSubscriber : public rclcpp::Node
{public:/* 公共构造函数将节点命名为minimal_subscriber */MinimalSubscriber(): Node("minimal_subscriber"){/* 初始化订阅者subscription_  ，使用Sphere消息类型、主题名称topic和在发生备份时限制消息所需的队列大小10，订阅话题回调函数topic_callback */subscription_ = this->create_subscription<tutorial_interfaces::msg::Sphere>(  // CHANGE"topic", 10, std::bind(&MinimalSubscriber::topic_callback, this, _1));}private:/* 定义订阅话题回调函数 */void topic_callback(const tutorial_interfaces::msg::Sphere & msg) const  // CHANGE{/* 打印话题消息的球体半径信息 */RCLCPP_INFO_STREAM(this->get_logger(), "I heard: '" << msg.radius << "'");}/* 订阅者字段的声明 */rclcpp::Subscription<tutorial_interfaces::msg::Sphere >::SharedPtr subscription_;  // CHANGE
};int main(int argc, char * argv[])
{/* 初始化ROS2 */rclcpp::init(argc, argv);/* 运行节点MinimalSubscriber*/rclcpp::spin(std::make_shared<MinimalSubscriber>());/* 退出ROS2 */rclcpp::shutdown();return 0;
}

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4. 修改依赖关系

在package.xml清单文件中，添加对自定义消息的依赖项的声明

<depend>tutorial_interfaces</depend>

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5. 修改编译信息

在CMakeLists.txt编译文件中

1. 更换搜索库 tutorial_interfaces
2. 更换可执行文件目标依赖关系 tutorial_interfaces

#...find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(tutorial_interfaces REQUIRED)                      # CHANGEadd_executable(talker src/publisher_member_function.cpp)
ament_target_dependencies(talker rclcpp tutorial_interfaces)    # CHANGEadd_executable(listener src/subscriber_member_function.cpp)
ament_target_dependencies(listener rclcpp tutorial_interfaces)  # CHANGEinstall(TARGETStalkerlistenerDESTINATION lib/${PROJECT_NAME})ament_package()

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6. 编译和运行

进入工作空间根目录

cd ~/ros2_ws

编译：

colcon build --packages-select cpp_pubsub

打开一个新终端，运行话题发布节点：

ros2 run cpp_pubsub talker# [INFO] [minimal_publisher]: Publishing: '0'
# [INFO] [minimal_publisher]: Publishing: '1'
# [INFO] [minimal_publisher]: Publishing: '2'

打开一个新终端，运行话题订阅节点：

ros2 run cpp_pubsub listener# [INFO] [minimal_subscriber]: I heard: '10'
# [INFO] [minimal_subscriber]: I heard: '11'
# [INFO] [minimal_subscriber]: I heard: '12'

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谢谢