Hello Xiaochen,
Parameters are not yet available for use with ROS 2 in MATLAB or Simulink. They are on our radar as we work to bring ROS 2 up to feature-parity with ROS, but are not yet in the toolbox.
Unfortunately, there isn't really a workaround to access parameters using other techniques in MATLAB alone. There are a couple of ways I can think of to access parameters, or have a parameter-like feature:
One works if the parameters are not expected to be modified external to a node. You can have a publisher that serves a simliar function to your parameter server on each node. Its message is just a list of parameter names and values. It only needs to publish once (or any time the parameter values change), but should use the value "Transient Local" for the "Durability" and a value of 1 for the "Depth" Quality of Service settings. Then when you need the parameter values, you can create a subscriber (also with Transient Local), and it will receive the most recently published message on that topic.
Another way would be to create a service server to act as the parameter server in ROS code outside of MATLAB. You could create it so that the request message provides the name of the parameter to get (or name and value to set, and indicates which it wants to do), and the response contains the current value. It would simply be querying the real parameter server under the hood, but this would depend on you having ROS installed on your system outside of MATLAB.
-Cam
