Initialise input ports in code

[benoit-robotics]

Hello,

I can't get my head around how to initialise the input ports of a node in the c++ code. I know how to initialise a port in the xml file.

I initialise my tree this way. For the sake of simplicity there is only one node.

  BT::BehaviorTreeFactory factory;
  // node
  factory.registerNodeType<PickUpObject>("PickUpObject");

  auto tree = factory.createTreeFromFile(tree_path);
  tree.tickRoot();

I want to find a way to set the value of an input port of the node in the code above. How can I do that ?
Thank you

[asasine]

You can get the blackboard of a tree using the rootBlackboard() method of the BT::Tree class

BT::BehaviorTreeFactory factory;
// node
factory.registerNodeType<PickUpObject>("PickUpObject");

auto tree = factory.createTreeFromFile(tree_path);

// initialize some values before ticking the tree's root
auto blackboard = tree.rootBlackboard();
blackboard->set("key", "value");

tree.tickRoot();

The rootBlackboard() method is declared here

BehaviorTree.CPP/include/behaviortree_cpp_v3/bt_factory.h

Line 215 in 8db5593

Blackboard::Ptr rootBlackboard();

And the BT::Blackboard class is declared here

BehaviorTree.CPP/include/behaviortree_cpp_v3/blackboard.h

Line 23 in 8db5593

class Blackboard

[benoit-robotics]

Thank you, I will give it a try. I was thinking of another way to do what I want : the constructor of a SyncActionNode takes a NodeConfiguration object and it seems to be possible to initialise the input ports through this object. But I don't know how to call this constructor using the factory object. Maybe there is another way to initialize a tree ?

[benoit-robotics]

@asasine I tried your solution but it appears that the default value of the input port ( the one that I set in the xml ) is still the one that I get when I retrieve the port value with :
getInput<std::string>("key").value();

Apparently, a hacky solution is to get the port value with :
config().blackboard->get<std::string>("key");

[asasine]

If you're also setting the input port in the behavior tree using the SetBlackboard action node, it will overwrite the blackboard entry when it's ticked.

Something worth noting is that subtrees don't share a blackboard with the root tree. If there's a subtree in the real tree you're testing, it has its own blackboard, therefore setting a key in tree.rootBlackboard()->set("key", "value") will not propagate to subtree blackboards automatically. You mentioned the tree you provided in this issue is simplified, so it seemed worth mentioning this caveat.

[facontidavide]

The suggested solution

auto blackboard = tree.rootBlackboard();
blackboard->set("key", "value");

will NOT work when you have subtrees, unless that specific entry port was remapped.

Keep blackboard scope in mind, when initializing!

The idiomatic way to do it in the XML is with SetBlackboard (version 3.X) or Script (version 4.X)

[zflat]

You could also register a simple action and bind your initial values to declared output ports like this:

factory.registerSimpleAction("GetInitialLocation",
  [this](BT::TreeNode& self) -> BT::NodeStatus {
    self.setOutput<std::string>("location", this->getInitialLocation());
    return BT::NodeStatus::SUCCESS;
  }, {
    BT::OutputPort<std::string>("location")
});