ROS2与C++入门教程-创建和使用插件

说明：

• 学习使用pluginlib创建和加载一个简单的插件

步骤：

• 安装pluginlib

sudo apt-get install ros-foxy-pluginlib

• 创建一个新包

cd dev_ws/src
ros2 pkg create --build-type ament_cmake polygon_base --dependencies pluginlib --node-name area_node

• 编辑文件

vim dev_ws/src/polygon_base/include/polygon_base/regular_polygon.hpp

• 添加以下内容

#ifndef POLYGON_BASE_REGULAR_POLYGON_HPP
#define POLYGON_BASE_REGULAR_POLYGON_HPP

namespace polygon_base
{
  class RegularPolygon
  {
    public:
      virtual void initialize(double side_length) = 0;
      virtual double area() = 0;
      virtual ~RegularPolygon(){}

    protected:
      RegularPolygon(){}
  };
}  // namespace polygon_base

#endif  // POLYGON_BASE_REGULAR_POLYGON_HPP

• 在dev_ws/src/polygon_base/CMakeLists.txt添加。在ament_target_dependencies命令后添加以下行

install(
  DIRECTORY include/
  DESTINATION include
)

• 在命令之前添加此ament_package命令

ament_export_include_directories(
  include
)

• 创建插件包

cd dev_ws/src
ros2 pkg create --build-type ament_cmake polygon_plugins --dependencies polygon_base pluginlib --library-name polygon_plugins

• 编辑文件

vim dev_ws/src/polygon_plugins/src/polygon_plugins.cpp
#include <polygon_base/regular_polygon.hpp>
#include <cmath>

namespace polygon_plugins
{
  class Square : public polygon_base::RegularPolygon
  {
    public:
      void initialize(double side_length) override
      {
        side_length_ = side_length;
      }

      double area() override
      {
        return side_length_ * side_length_;
      }

    protected:
      double side_length_;
  };

  class Triangle : public polygon_base::RegularPolygon
  {
    public:
      void initialize(double side_length) override
      {
        side_length_ = side_length;
      }

      double area() override
      {
        return 0.5 * side_length_ * getHeight();
      }

      double getHeight()
      {
        return sqrt((side_length_ * side_length_) - ((side_length_ / 2) * (side_length_ / 2)));
      }

    protected:
      double side_length_;
  };
}

#include <pluginlib/class_list_macros.hpp>

PLUGINLIB_EXPORT_CLASS(polygon_plugins::Square, polygon_base::RegularPolygon)
PLUGINLIB_EXPORT_CLASS(polygon_plugins::Triangle, polygon_base::RegularPolygon)

• 创建XML文件，在dev_ws/src/polygon_plugins/plugins.xml添加以下内容

<library path="polygon_plugins">
      <class type="polygon_plugins::Square" base_class_type="polygon_base::RegularPolygon">
        <description>This is a square plugin.</description>
      </class>
      <class type="polygon_plugins::Triangle" base_class_type="polygon_base::RegularPolygon">
        <description>This is a triangle plugin.</description>
      </class>
    </library>

• 在dev_ws/src/polygon_plugins/CMakeLists.txt添加以下内容

add_library(polygon_plugins src/polygon_plugins.cpp)
target_include_directories(polygon_plugins PUBLIC
<BUILD_INTERFACE:${CMAKE_CURRENT_SOURCE_DIR}/include>
<INSTALL_INTERFACE:include>)
ament_target_dependencies(
  polygon_plugins
  polygon_base
  pluginlib
)

pluginlib_export_plugin_description_file(polygon_base plugins.xml)

install(
  TARGETS polygon_plugins
  EXPORT export_${PROJECT_NAME}
  ARCHIVE DESTINATION lib
  LIBRARY DESTINATION lib
  RUNTIME DESTINATION bin
)

• 在ament_package命令之前，添加

    ament_export_libraries(
  polygon_plugins
)
ament_export_targets(
  export_${PROJECT_NAME}
)

• 使用插件。在dev_ws/src/polygon_base/src/area_node.cpp添加以下内容

#include <pluginlib/class_loader.hpp>
#include <polygon_base/regular_polygon.hpp>

int main(int argc, char** argv)
{
  // To avoid unused parameter warnings
  (void) argc;
  (void) argv;

  pluginlib::ClassLoader<polygon_base::RegularPolygon> poly_loader("polygon_base", "polygon_base::RegularPolygon");

  try
  {
    std::shared_ptr<polygon_base::RegularPolygon> triangle = poly_loader.createSharedInstance("polygon_plugins::Triangle");
    triangle->initialize(10.0);

    std::shared_ptr<polygon_base::RegularPolygon> square = poly_loader.createSharedInstance("polygon_plugins::Square");
    square->initialize(10.0);

    printf("Triangle area: %.2f\n", triangle->area());
    printf("Square area: %.2f\n", square->area());
  }
  catch(pluginlib::PluginlibException& ex)
  {
    printf("The plugin failed to load for some reason. Error: %s\n", ex.what());
  }

  return 0;
}

• 构建和运行

cd dev_ws
colcon build --packages-select polygon_base polygon_plugins
. install/setup.bash

• 运行节点

ros2 run polygon_base area_node

• 运行结果

Triangle area: 43.30
Square area: 100.00