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 completes
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();
}

// Called once when the goal becomes active
void activeCb()
{
  ROS_INFO("Goal just went active");
}

// Called every time feedback is received for the goal
void 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。