t08_additional_node_args.cpp

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#include "behaviortree_cpp_v3/bt_factory.h"
 
using namespace BT;
 
/*
 * Sometimes, it is convenient to pass additional (static) arguments to a Node.
 * If these parameters are known at compilation time or at deployment-time
 * and they don't change at run-time, input ports are probably overkill and cumbersome.
 *
 * This tutorial demonstrates two possible ways to initialize a custom node with
 * additional arguments.
 */
 
// Action_A has a different constructor than the default one.
class Action_A : public SyncActionNode
{
public:
  // additional arguments passed to the constructor
  Action_A(const std::string& name, const NodeConfiguration& config, int arg1,
           double arg2, std::string arg3) :
    SyncActionNode(name, config), _arg1(arg1), _arg2(arg2), _arg3(arg3)
  {}
 
  NodeStatus tick() override
  {
    std::cout << "Action_A: " << _arg1 << " / " << _arg2 << " / " << _arg3 << std::endl;
    return NodeStatus::SUCCESS;
  }
  static PortsList providedPorts()
  {
    return {};
  }
 
private:
  int _arg1;
  double _arg2;
  std::string _arg3;
};
 
// Action_B implements an init(...) method that must be called once at the beginning.
class Action_B : public SyncActionNode
{
public:
  Action_B(const std::string& name, const NodeConfiguration& config) :
    SyncActionNode(name, config)
  {}
 
  // we want this method to be called ONCE and BEFORE the first tick()
  void init(int arg1, double arg2, std::string arg3)
  {
    _arg1 = (arg1);
    _arg2 = (arg2);
    _arg3 = (arg3);
  }
 
  NodeStatus tick() override
  {
    std::cout << "Action_B: " << _arg1 << " / " << _arg2 << " / " << _arg3 << std::endl;
    return NodeStatus::SUCCESS;
  }
  static PortsList providedPorts()
  {
    return {};
  }
 
private:
  int _arg1;
  double _arg2;
  std::string _arg3;
};
 
// Simple tree, used to execute once each action.
static const char* xml_text = R"(
 
 <root >
     <BehaviorTree>
        <Sequence>
            <Action_A/>
            <Action_B/>
        </Sequence>
     </BehaviorTree>
 </root>
 )";
 
int main()
{
  BehaviorTreeFactory factory;
 
  // A node builder is nothing more than a function pointer to create a
  // std::unique_ptr<TreeNode>.
  // Using lambdas or std::bind, we can easily "inject" additional arguments.
  NodeBuilder builder_A = [](const std::string& name, const NodeConfiguration& config) {
    return std::make_unique<Action_A>(name, config, 42, 3.14, "hello world");
  };
 
  // BehaviorTreeFactory::registerBuilder is the more general way to register a custom node.
  // Not the most user friendly, but definitely the most flexible one.
  factory.registerBuilder<Action_A>("Action_A", builder_A);
 
  // The regitration of  Action_B is done as usual, but we still need to call Action_B::init()
  factory.registerNodeType<Action_B>("Action_B");
 
  auto tree = factory.createTreeFromText(xml_text);
 
  // Iterate through all the nodes and call init if it is an Action_B
  for (auto& node : tree.nodes)
  {
    if (auto action_B_node = dynamic_cast<Action_B*>(node.get()))
    {
      action_B_node->init(69, 9.99, "interesting_value");
    }
  }
 
  tree.tickRootWhileRunning();
 
  /* Expected output:
 
        Action_A: 42 / 3.14 / hello world
        Action_B: 69 / 9.99 / interesting_value
    */
  return 0;
}