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I am looking to replicate ROS1 behaviour where I could use ShapeShifter to subscribe to any topic, and not have to specify the message type. This code would run in C++.
I have found this Pull Request but it seems nothing has yet come of this.
Does anyone know if this is possible in ROS2 using C++? If not C++, then Python?
Many thanks
Not completely what are looking for, but here is one way to do in Python. In Python, you can use get_msg_class from ros2topic.api to get the message type and then subscribe to the topic. Here is an example:
import rclpy
from rclpy.node import Node
from ros2topic.api import get_msg_class
class TestSubscriber(Node):
def __init__(self):
super().__init__('test_subscriber')
message_type = get_msg_class(self, '/topic_name', include_hidden_topics=True)
print('Message type:', message_type)
self.create_subscription(message_type, '/topic_name', self.on_message_received, 1)
def on_message_received(self, message):
print(message)
def main(args=None):
rclpy.init(args=args)
test_subscriber = TestSubscriber()
rclpy.spin(test_subscriber)
test_subscriber.destroy_node()
rclpy.shutdown()
if __name__ == '__main__':
main()
Test it by running e.g.:
ros2 topic pub /topic_name std_msgs/String '{ data: test_value }'
Take a look at rosbag2, it subscribes to serialized topics regardless of message type.
For anyone looking for a cpp solution:
#include <memory>
#include <string>
#include "rclcpp/rclcpp.hpp"
#include "rclcpp/generic_subscription.hpp"
#include "std_msgs/msg/string.hpp"
using std::placeholders::_1;
class MinimalSubscriber : public rclcpp::Node
{
public:
MinimalSubscriber()
: Node("minimal_subscriber")
{
auto data = rclcpp::Node::get_topic_names_and_types();
auto msg_type = data["/topic_name"];
for(auto type : msg_type){
std::cout << type << std::endl;
rclcpp::QoS qos = rclcpp::QoS(10);
std::function<void(std::shared_ptr<rclcpp::SerializedMessage>)> call = std::bind(&MinimalSubscriber::topic_callback, this, _1);
subscription_ = this->create_generic_subscription("/topic_name",type ,qos, call );
}
}
private:
void topic_callback(std::shared_ptr<rclcpp::SerializedMessage> msg)
{
RCLCPP_INFO(this->get_logger(), "I heard:");
}
std::shared_ptr<rclcpp::GenericSubscription> subscription_;
};
int main(int argc, char * argv[])
{
rclcpp::init(argc, argv);
rclcpp::spin(std::make_shared<MinimalSubscriber>());
rclcpp::shutdown();
return 0;
}
Asked: 2020-08-17 05:38:26 -0500
Seen: 2,010 times
Last updated: Jan 12 '23
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