在ROS1中,Parameter参数机制默认是无法实现动态监控的(需要配合专门的动态机制),比如正在使用的参数被其他节点改变了,如果不重新查询的话,就无法确定改变之后的值。ROS2最新版本中添加了参数的事件触发机制ParameterEventHandler, 当参数被改变后,可以通过回调函数的方式,动态发现参数修改结果。
一、创建功能包
ros2 pkg create --build-type ament_cmake cpp_parameter_event_handler --dependencies rclcpp
<description>C++ parameter tutorial</description>
<maintainer email="huchunxu@guyuehome.com">Hu Chunxu</maintainer>
<license>Apache License 2.0</license>
二、编写C++代码节点
#include <memory>
#include "rclcpp/rclcpp.hpp"
class SampleNodeWithParameters : public rclcpp::Node
{
public:
SampleNodeWithParameters()
: Node("node_with_parameters")
{
this->declare_parameter("an_int_param", 0);
// Create a parameter subscriber that can be used to monitor parameter changes
// (for this node's parameters as well as other nodes' parameters)
param_subscriber_ = std::make_shared<rclcpp::ParameterEventHandler>(this);
// Set a callback for this node's integer parameter, "an_int_param"
auto cb = [this](const rclcpp::Parameter & p) {
RCLCPP_INFO(
this->get_logger(), "cb: Received an update to parameter \"%s\" of type %s: \"%ld\"",
p.get_name().c_str(),
p.get_type_name().c_str(),
p.as_int());
};
cb_handle_ = param_subscriber_->add_parameter_callback("an_int_param", cb);
}
private:
std::shared_ptr<rclcpp::ParameterEventHandler> param_subscriber_;
std::shared_ptr<rclcpp::ParameterCallbackHandle> cb_handle_;
};
int main(int argc, char ** argv)
{
rclcpp::init(argc, argv);
rclcpp::spin(std::make_shared<SampleNodeWithParameters>());
rclcpp::shutdown();
return 0;
}
2.1 代码解析
SampleNodeWithParameters()
: Node("node_with_parameters")
{
this->declare_parameter("an_int_param", 0);
// Create a parameter subscriber that can be used to monitor parameter changes
// (for this node's parameters as well as other nodes' parameters)
param_subscriber_ = std::make_shared<rclcpp::ParameterEventHandler>(this);
// Set a callback for this node's integer parameter, "an_int_param"
auto cb = [this](const rclcpp::Parameter & p) {
RCLCPP_INFO(
this->get_logger(), "cb: Received an update to parameter \"%s\" of type %s: \"%ld\"",
p.get_name().c_str(),
p.get_type_name().c_str(),
p.as_int());
};
cb_handle_ = param_subscriber_->add_parameter_callback("an_int_param", cb);
}
2.2 添加配置选项
add_executable(parameter_event_handler src/parameter_event_handler.cpp)
ament_target_dependencies(parameter_event_handler rclcpp)
install(TARGETS
parameter_event_handler
DESTINATION lib/${PROJECT_NAME}
)
三、编译运行
rosdep install -i --from-path src --rosdistro $ROS_DISTRO -y
colcon build --packages-select cpp_parameter_event_handler
. install/setup.bash
ros2 run cpp_parameter_event_handler parameter_event_handler
ros2 param set node_with_parameters an_int_param 43
[INFO] [1606950498.422461764] [node_with_parameters]: cb: Received an update to parameter "an_int_param" of type integer: "43"
四、监控其他节点参数的变化
// Now, add a callback to monitor any changes to the remote node's parameter. In this
// case, we supply the remote node name.
auto cb2 = [this](const rclcpp::Parameter & p) {
RCLCPP_INFO(
this->get_logger(), "cb2: Received an update to parameter \"%s\" of type: %s: \"%.02lf\"",
p.get_name().c_str(),
p.get_type_name().c_str(),
p.as_double());
};
auto remote_node_name = std::string("parameter_blackboard");
auto remote_param_name = std::string("a_double_param");
cb_handle2_ = param_subscriber_->add_parameter_callback(remote_param_name, cb2, remote_node_name);
private:
std::shared_ptr<rclcpp::ParameterEventHandler> param_subscriber_;
std::shared_ptr<rclcpp::ParameterCallbackHandle> cb_handle_;
std::shared_ptr<rclcpp::ParameterCallbackHandle> cb_handle2_; // Add this
colcon build --packages-select cpp_parameter_event_handler
. install/setup.bash
ros2 run cpp_parameter_event_handler parameter_event_handler
ros2 run demo_nodes_cpp parameter_blackboard
ros2 param set parameter_blackboard a_double_param 3.45
[INFO] [1606952588.237531933] [node_with_parameters]: cb2: Received an update to parameter "a_double_param" of type: double: "3.45"
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