8.learningAction（行为库）3

在一些情况下，阻塞直到一个目标完成不会提供足够的灵活。相反的，基于事件运行或许需要更多场景。在以下例程中，提供如何使用回调来避免调用waitForResult()来阻塞用于目标完成。

/*fibonacci_callback_client.cpp*/#include <ros/ros.h>#include <actionlib/client/simple_action_client.h>#include <actionlib_tutorials/FibonacciAction.h>using namespace actionlib_tutorials;typedef actionlib::SimpleActionClient<FibonacciAction> Client;// Called once when the goal completesvoid doneCb(const actionlib::SimpleClientGoalState& state,            const FibonacciResultConstPtr& result){  ROS_INFO("Finished in state [%s]", state.toString().c_str());  ROS_INFO("Answer: %i", result->sequence.back());  ros::shutdown();}// Called once when the goal becomes activevoid activeCb(){  ROS_INFO("Goal just went active");}// Called every time feedback is received for the goalvoid feedbackCb(const FibonacciFeedbackConstPtr& feedback){  ROS_INFO("Got Feedback of length %lu", feedback->sequence.size());}int main (int argc, char **argv){  ros::init(argc, argv, "test_fibonacci_callback");  // Create the action client  Client ac("fibonacci", true);  ROS_INFO("Waiting for action server to start.");  ac.waitForServer();  ROS_INFO("Action server started, sending goal.");  // Send Goal  FibonacciGoal goal;  goal.order = 20;  ac.sendGoal(goal, &doneCb, &activeCb, &feedbackCb);  ros::spin();  return 0;}

当尝试注册类方法时，注册目标、活跃和反馈回调的语法并不是很方便。然而，这已经完成了，通过”超级有用但有时很难得到正确的语法” boost::bind

/*fibonacci_class_client.cpp*/#include <ros/ros.h>#include <actionlib/client/simple_action_client.h>#include <actionlib_tutorials/FibonacciAction.h>using namespace actionlib_tutorials;typedef actionlib::SimpleActionClient<FibonacciAction> Client;class MyNode{public:  MyNode() : ac("fibonacci", true)  {    ROS_INFO("Waiting for action server to start.");    ac.waitForServer();    ROS_INFO("Action server started, sending goal.");  }  void doStuff(int order)  {    FibonacciGoal goal;    goal.order = order;    // Need boost::bind to pass in the 'this' pointer    ac.sendGoal(goal,                boost::bind(&MyNode::doneCb, this, _1, _2),                Client::SimpleActiveCallback(),                Client::SimpleFeedbackCallback());  }  void doneCb(const actionlib::SimpleClientGoalState& state,              const FibonacciResultConstPtr& result)  {    ROS_INFO("Finished in state [%s]", state.toString().c_str());    ROS_INFO("Answer: %i", result->sequence.back());    ros::shutdown();  }private:  Client ac;};int main (int argc, char **argv){  ros::init(argc, argv, "test_fibonacci_class_client");  MyNode my_node;  my_node.doStuff(10);  ros::spin();  return 0;}

这个示例的关键所在是调用sendGoal ，该函数使用boost::bind

/*fibonacci_class_client.cpp*/#include <ros/ros.h>#include <actionlib/client/simple_action_client.h>#include <actionlib_tutorials/FibonacciAction.h>using namespace actionlib_tutorials;typedef actionlib::SimpleActionClient<FibonacciAction> Client;class MyNode{public:  MyNode() : ac("fibonacci", true)  {    ROS_INFO("Waiting for action server to start.");    ac.waitForServer();    ROS_INFO("Action server started, sending goal.");  }  void doStuff(int order)  {    FibonacciGoal goal;    goal.order = order;    // Need boost::bind to pass in the 'this' pointer    ac.sendGoal(goal,                boost::bind(&MyNode::doneCb, this, _1, _2),                Client::SimpleActiveCallback(),                Client::SimpleFeedbackCallback());  }  void doneCb(const actionlib::SimpleClientGoalState& state,              const FibonacciResultConstPtr& result)  {    ROS_INFO("Finished in state [%s]", state.toString().c_str());    ROS_INFO("Answer: %i", result->sequence.back());    ros::shutdown();  }private:  Client ac;};int main (int argc, char **argv){  ros::init(argc, argv, "test_fibonacci_class_client");  MyNode my_node;  my_node.doStuff(10);  ros::spin();  return 0;}

我们不注册活跃或反馈回调函数，因此我们可以使用传递null函数指针来代替。我们也可以通过设置两个参数为空来使用，因为默认的回调函数为null。