Appropriate way to obtain data in behavior tree and the corresponding controller(s)

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Dear all,

In the example of nav2 dynamic object following, the developer says someting about reading a topic between the second and third code block but this does not appear to be done from within the XML file.

My question is: What is the appropriate way to read a topic within a BT node?

I also would like to also know a more general approach to how the dataflow between the behavior tree node and the corresponding cotrollers is handeled?

I posted this question already at discource for the people who would like to discus the design aspects of the BT modules with corresponding controllers, planner or recoverie behaniors.

Kind regards, Kevin