ros下的plugin学习

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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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