ros下的plugin学习

昨天看了ros下的plugin教程，今天整理一下，教程网址如下：http://wiki.ros.org/pluginlib/Tutorials/Writing%20and%20Using%20a%20Simple%20Plugin

所谓插件plugin个人理解就是把一个写好的类按照ros下标准格式封装一下，然后就可以直接按照ros下的标准格式进行调用。这样方便移植和分享给其他人用，相当于一个动态链接库。

1、catkin_ws/src/pluginlib_tutorials_/include/pluginlib_tutorials_/polygon_base.h建立基类

#ifndef PLUGINLIB_TUTORIALS__POLYGON_BASE_H_
#define PLUGINLIB_TUTORIALS__POLYGON_BASE_H_

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

    protected:
      RegularPolygon(){}
  };
};
#endif

上面的代码应该非常自我解释...我们正在创建一个名为RegularPolygon的抽象类。有一件事要注意的是初始化方法的存在。使用pluginlib，类不需要参数的构造函数，所以如果需要任何参数，我们使用initialize方法初始化对象。RegularPolygon是一个基类，同时定义了几种纯虚函数，作为一个基类的模板，具体的实现在继承类里面进行实体化。
2、 include/pluginlib_tutorials_/polygon_plugins.h建立继承类

#ifndef PLUGINLIB_TUTORIALS__POLYGON_PLUGINS_H_
#define PLUGINLIB_TUTORIALS__POLYGON_PLUGINS_H_
#include <pluginlib_tutorials_/polygon_base.h>
#include <cmath>

namespace polygon_plugins
{
  class Triangle : public polygon_base::RegularPolygon
  {
    public:
      Triangle(){}

      void initialize(double side_length)
      {
        side_length_ = side_length;
      }

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

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

    private:
      double side_length_;
  };

  class Square : public polygon_base::RegularPolygon
  {
    public:
      Square(){}

      void initialize(double side_length)
      {
        side_length_ = side_length;
      }

      double area()
      {
        return side_length_ * side_length_;
      }

    private:
      double side_length_;

  };
};
#endif

这两个继承类将作为我们的插件

3、src/polygon_plugins.cpp注册一个插件

#include <pluginlib/class_list_macros.h>
#include <pluginlib_tutorials_/polygon_base.h>
#include <pluginlib_tutorials_/polygon_plugins.h>

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

4、 CMakeLists.txt修改功能包的cmakelist这样就可以编译生成库文件

add_library(polygon_plugins src/polygon_plugins.cpp)

然后在功能包的根目录下catkin_make

5、增加一个配置文件说明该插件的功能，

在package.xml的同级目录下新建polygon_plugins.xml:

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

然后修改功能包的配置文件package.xml来告诉编译器有了这个插件

<export>
  <pluginlib_tutorials_ plugin="${prefix}/polygon_plugins.xml" />
</export>

6、验证插件是否正常

rospack plugins --attrib=plugin pluginlib_tutorials_

7、 src/polygon_loader.cpp调用一个插件

#include <pluginlib/class_loader.h>
#include <pluginlib_tutorials_/polygon_base.h>

int main(int argc, char** argv)
{
  pluginlib::ClassLoader<polygon_base::RegularPolygon> poly_loader("pluginlib_tutorials_", "polygon_base::RegularPolygon");

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

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

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

  return 0;
}

CMakeLists.txt添加 ：

include_directories(include)
add_executable(polygon_loader src/polygon_loader.cpp)
target_link_libraries(polygon_loader ${catkin_LIBRARIES})

然后catkin_make

运行生成的可行文件

devel/lib/pluginlib_tutorials_/polygon_loader

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