Using message_filters::Synchronizer inside class

edit

Generally, I would like to see some progress or efforts instead of answering directly because this is how we learn new things by exploring and trying. Anyway, below is the code which is extended from the previous answer. In order to test it, I used image and camera info. So please change the camera info to depth accordingly.

#include <message_filters/subscriber.h>
#include <message_filters/sync_policies/approximate_time.h>
#include <message_filters/synchronizer.h>
#include <ros/ros.h>
#include <sensor_msgs/CameraInfo.h>
#include <sensor_msgs/Image.h>

#include <memory>

using namespace sensor_msgs;
using namespace message_filters;

class ClientHandler
{
public:
  ClientHandler(ros::NodeHandle& nh, std::string& rgb_topic, std::string& cam_info_topic);
  void MyCallback(const ImageConstPtr& image, const CameraInfoConstPtr& cam_info);

private:
  using MySyncPolicy = sync_policies::ApproximateTime<Image, CameraInfo>;

  ros::NodeHandle _nh;
  message_filters::Subscriber<Image> _rgb_sub;
  message_filters::Subscriber<CameraInfo> _camera_info_sub;
  std::shared_ptr<message_filters::Synchronizer<MySyncPolicy> > _sync;
};

ClientHandler::ClientHandler(ros::NodeHandle& nh, std::string& rgb_topic, std::string& cam_info_topic) : _nh(nh)
{
  _rgb_sub.subscribe(_nh, rgb_topic, 1);
  _camera_info_sub.subscribe(_nh, cam_info_topic, 1);

  _sync = std::make_shared<message_filters::Synchronizer<MySyncPolicy> >(10);
  _sync->connectInput(_rgb_sub, _camera_info_sub);
  _sync->registerCallback(boost::bind(&ClientHandler::MyCallback, this, _1, _2));
}

void ClientHandler::MyCallback(const ImageConstPtr& image, const CameraInfoConstPtr& cam_info)
{
  ROS_INFO("Sequence: [%d] [%d]", image->header.seq, cam_info->header.seq);
}

int main(int argc, char** argv)
{
  ros::init(argc, argv, "image_listener");
  ros::NodeHandle n;

  std::string rgbTopic = "/usb_cam/image_raw";
  std::string camInfoTopic = "/usb_cam/camera_info";
  ClientHandler ClientHandler(n, rgbTopic, camInfoTopic);

  ros::spin();
  return 0;
}

I used the usb_cam package to publish my webcam and used the above node to subscribe, as shown below:

$ rosrun usb_cam usb_cam_node
$ rosrun beginner_tutorials listener_class_filter_sync 
[ INFO] [1664204780.217148024]: Sequence: [0] [368]
[ INFO] [1664204780.249005396]: Sequence: [1] [369]
[ INFO] [1664204780.280544030]: Sequence: [2] [370]
[ INFO] [1664204780.316463488]: Sequence: [3] [371]
[ INFO] [1664204780.348469919]: Sequence: [4] [372]
[ INFO] [1664204780.380547970]: Sequence: [5] [373]
[ INFO] [1664204780.416397331]: Sequence: [6] [374]
[ INFO] [1664204780.448968855]: Sequence: [7] [375]
[ INFO] [1664204780.484444885]: Sequence: [8] [376]
[ INFO] [1664204780.516418570]: Sequence: [9] [377]
[ INFO] [1664204780.548350255]: Sequence: [10] [378]