ROS Image subscriber - window popup does not appear - opencv

Question

I am following image subscribe tutorial on official ROS page. when I run my_subscriber no window popup appears. I type -
rosrun image_transport_tutorial my_subscriber
output is -
init done
opengl support available
And then nothing happens. (even the output "init done" is unexplained because there is not output line in my_subscriber.cpp)
I am following this tutorial - ROS tutorial
I have roscore and rosrun image_transport_tutorial my_publisher pathtofile already running in dofferent terminals.
I checked that publisher is publishing by running command
rostopic list -v
my_subscriber file has the following contents -
#include <ros/ros.h>
#include <ros/ros.h>
#include <image_transport/image_transport.h>
#include <opencv2/highgui/highgui.hpp>
#include <cv_bridge/cv_bridge.h>
#include <stdio.h>
void imageCallback(const sensor_msgs::ImageConstPtr& msg)
{
try
{
cv::imshow("view", cv_bridge::toCvShare(msg, "bgr8")->image);
}
catch (cv_bridge::Exception& e)
{
ROS_ERROR("Could not convert from '%s' to 'bgr8'.", msg->encoding.c_str());
}
}
int main(int argc, char **argv)
{
std::cout<<"kapil";
ros::init(argc, argv, "image_listener");
ros::NodeHandle nh;
cv::namedWindow("view");
cv::startWindowThread();
image_transport::ImageTransport it(nh);
image_transport::Subscriber sub = it.subscribe("camera/image", 1, imageCallback);
ros::spin();
cv::destroyWindow("view");
}
Solved : I added waitKey function in the try block as suggested in one of the answers.
cv::waitKey(30);

Answer 1

According to the comment to this answer, using cv::startWindowThread() does not always work. Maybe this is the issue in your case.
Try to add cv::waitKey(10) after cv::imshow instead. This will wait for some key press for 10 milliseconds, giving the window time to show the image.
(This always seemed to me like a dirty hack, but it is the common way to show images in OpenCV...)