ros::Timer in ModelPlugin

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Hi everyone!

I want to set a timer's callback for ModelPlugin. What is the better way to do it?

I tried such way but got error:

"error: invalid use of incomplete type ‘class ros::NodeHandle’ timer = nh->createTimer(ros::Duration(0.1), timerCallback);"

Code:

namespace gazebo
{
class VelodynePlugin : public ModelPlugin
{
...
private: ros::NodeHandlePtr nh;
ros::Timer timer;

public: void timerCallback()
    {
        cout << "Hi Vlad!" << endl;
    }

public: virtual void Load(physics::ModelPtr _model, sdf::ElementPtr _sdf)
    {
        ...
        nh = boost::make_shared<ros::NodeHandle>();
        timer = nh->createTimer(ros::Duration(0.1), timerCallback);
    }
...
}

Where is a mistake?