Any reason why examples use a timer instead of ParameterEventHandler?

[danielcranston]

Seems like a lost opportunity to showcase best practices. Using a ParameterEventHandler (C++/Python) seems like a nicer fit when checking for updates instead of using a timer that polls for changes every x seconds.

I'd be happy to make a PR, just want check in case there's a reason behind it I'm not aware of.

[amarburg]

+1 It would be good to have a canonical code sample / example for receiving a callback on a parameter change and using this package (for the validation, etc).

Best I have so far is something like

...
param_listener_ =  std::make_shared<ParamListener>(get_node_parameters_interface());
callback_handle_ = this->add_on_set_parameters_callback(std::bind(
        &MyNode::parametersCallback, this, std::placeholders::_1));
...


rcl_interfaces::msg::SetParametersResult parametersCallback(
      const std::vector<rclcpp::Parameter> &parameters) {

    param_listener_->update(parameters);
    auto params = param_listener_->get_params();

    // use params
}

This is functional, but doesn't sit right, as the listener is update()'ed twice, once here and once in the internal callback within the ParamListener?