Beginner：Client libraries-6创建自定义的msg和srv文件

目标：定义自定义接口文件(.msg和.srv)，在c++节点和Python中使用他们。

背景

有时候需要定义自己的消息和服务。之前教程都是已经定义好的系统的消息类型，本教程介绍最简单的自定义接口定义的方法。

任务

1、创建一个包

ros2 pkg create --build-type ament_cmake tutorial_interfaces

2、创建自定义消息

2.1 msg定义

创建了两个文件Num.msg以及Sphere.msg

2.2 srv定义

创建文件AddThreeInts.srv

3. CMakeLists.txt

将自定义的类型转换为具体语言可识别的消息，在CMakeLists.txt中添加如下

find_package(geometry_msgs REQUIRED)
find_package(rosidl_default_generators REQUIRED)

rosidl_generate_interfaces(${PROJECT_NAME}
  "msg/Num.msg"
  "msg/Sphere.msg"
  "srv/AddThreeInts.srv"
  DEPENDENCIES geometry_msgs # Add packages that above messages depend on, in this case geometry_msgs for Sphere.msg
)

cmake_minimum_required(VERSION 3.8)
project(tutorial_interfaces)

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

rosidl_generate_interfaces(${PROJECT_NAME}
"msg/Num.msg"
"msg/Sphere.msg"
"srv/AddThreeInts.srv"

DEPENDENCIES geometry_msgs)

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()

注意：在rosidl_generate_interfaces中的第一个参数必须是${PROJECT_NAME}

4、package.xml

因为定义的信息依赖于rosidl_default_generators用于生成制定的语言代码，需要声明编译工具依赖它。rosidl_default_runtime是运行时或者执行阶段的依赖，在之后使用消息时被需要。rosidl_interface_packages是你包的依赖组的名字。tutorial_interfaces应与关联，并使用<member_of_group>标记声明。

<?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>tutorial_interfaces</name>
  <version>0.0.0</version>
  <description>TODO: Package description</description>
  <maintainer email="stardust@todo.todo">stardust</maintainer>
  <license>TODO: License declaration</license>

  <buildtool_depend>ament_cmake</buildtool_depend>
  <depend>geometry_msgs</depend>
  <buildtool_depend>rosidl_default_generator</buildtool_depend>

  <exec_depend>rosidl_default_runtime</exec_depend>
  <test_depend>ament_lint_auto</test_depend>
  <test_depend>ament_lint_common</test_depend>
  <member_of_group>rosidl_interface_packages</member_of_group>
  <export>
    <build_type>ament_cmake</build_type>
  </export>
</package>

5、编译并运行

colcon build --packages-select tutorial_interfaces

检查是否有消息

ros2 interface show tutorial_interfaces/msg/Num

ros2 interface show tutorial_interfaces/msg/Sphere

ros2 interface show tutorial_interfaces/srv/AddThreeInts

6、测试自定义消息

6.1 用发布器和订阅器来测试Num.msg

发布者

#include <chrono>
#include <memory>

#include "rclcpp/rclcpp.hpp"
#include "tutorial_interfaces/msg/num.hpp"                                            // CHANGE

using namespace std::chrono_literals;

class MinimalPublisher : public rclcpp::Node
{
public:
  MinimalPublisher()
  : Node("minimal_publisher"), count_(0)
  {
    publisher_ = this->create_publisher<tutorial_interfaces::msg::Num>("topic", 10);  // CHANGE
    timer_ = this->create_wall_timer(
      500ms, std::bind(&MinimalPublisher::timer_callback, this));
  }

private:
  void timer_callback()
  {
    auto message = tutorial_interfaces::msg::Num();                                   // CHANGE
    message.num = this->count_++;                                                     // CHANGE
    RCLCPP_INFO_STREAM(this->get_logger(), "Publishing: '" << message.num << "'");    // CHANGE
    publisher_->publish(message);
  }
  rclcpp::TimerBase::SharedPtr timer_;
  rclcpp::Publisher<tutorial_interfaces::msg::Num>::SharedPtr publisher_;             // CHANGE
  size_t count_;
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalPublisher>());
  rclcpp::shutdown();
  return 0;
}

订阅者

#include <functional>
#include <memory>

#include "rclcpp/rclcpp.hpp"
#include "tutorial_interfaces/msg/num.hpp"                                       // CHANGE

using std::placeholders::_1;

class MinimalSubscriber : public rclcpp::Node
{
public:
  MinimalSubscriber()
  : Node("minimal_subscriber")
  {
    subscription_ = this->create_subscription<tutorial_interfaces::msg::Num>(    // CHANGE
      "topic", 10, std::bind(&MinimalSubscriber::topic_callback, this, _1));
  }

private:
  void topic_callback(const tutorial_interfaces::msg::Num & msg) const  // CHANGE
  {
    RCLCPP_INFO_STREAM(this->get_logger(), "I heard: '" << msg.num << "'");     // CHANGE
  }
  rclcpp::Subscription<tutorial_interfaces::msg::Num>::SharedPtr subscription_;  // CHANGE
};

int main(int argc, char * argv[])
{
  rclcpp::init(argc, argv);
  rclcpp::spin(std::make_shared<MinimalSubscriber>());
  rclcpp::shutdown();
  return 0;
}

CMakeLists.txt

#...

find_package(ament_cmake REQUIRED)
find_package(rclcpp REQUIRED)
find_package(tutorial_interfaces REQUIRED)                      # CHANGE

add_executable(talker src/publisher_member_function.cpp)
ament_target_dependencies(talker rclcpp tutorial_interfaces)    # CHANGE

add_executable(listener src/subscriber_member_function.cpp)
ament_target_dependencies(listener rclcpp tutorial_interfaces)  # CHANGE

install(TARGETS
  talker
  listener
  DESTINATION lib/${PROJECT_NAME})

ament_package()

package.xml

<?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_pubsub</name>
  <version>0.0.0</version>
  <description>TODO: Package description</description>
  <maintainer email="stardust@todo.todo">stardust</maintainer>
  <license>TODO: License declaration</license>

  <buildtool_depend>ament_cmake</buildtool_depend>

  <test_depend>ament_lint_auto</test_depend>
  <test_depend>ament_lint_common</test_depend>
  <depend>rclcpp</depend>
  <depend>std_msgs</depend>
  <depend>tutorial_interfaces</depend>
  <export>
    <build_type>ament_cmake</build_type>
  </export>
</package>