Load external subtree from inline XML throws std::runtime_error

Describe the bug

When I include a custom subtree (called MyTree in this example) from an XML file, it does not work when I specify my root tree inline as string. It throws the following error:

terminate called after throwing an instance of 'std::runtime_error'
what():  Can't find a tree with name: MyTree

However, when I create that same subtree directly or when I include it in another tree that I load from an XML file, everything works fine.

How to Reproduce

This fails:

#include <behaviortree_cpp/bt_factory.h>

int main(int argc, char ** argv)
{
  BT::BehaviorTreeFactory factory;
  factory.registerBehaviorTreeFromFile("/path/to/my_tree.xml");
  std::string tree_xml =
    R"(
    <root BTCPP_format="4" >
        <BehaviorTree ID="TestTree">
            <SubTree ID="MyTree"/>
        </BehaviorTree>
    </root>)";
  auto tree = factory.createTreeFromText(tree_xml);
  auto status = tree.tickWhileRunning();
  return 0;
}

This works:

#include <behaviortree_cpp/bt_factory.h>

int main(int argc, char ** argv)
{
  BT::BehaviorTreeFactory factory;
  factory.registerBehaviorTreeFromFile("/path/to/my_tree.xml");
  auto tree = factory.createTree("MyTree");
  auto status = tree.tickWhileRunning();
  return 0;
}

Describe the bug 描述错误

When I include a custom subtree (called MyTree in this example) from an XML file, it does not work when I specify my root tree inline as string. It throws the following error:当我从 XML 文件中包含自定义子树（在本示例中称为MyTree ）时，当我将根树内联指定为字符串时，它不起作用。它抛出以下错误：

terminate called after throwing an instance of 'std::runtime_error'
what():  Can't find a tree with name: MyTree

However, when I create that same subtree directly or when I include it in another tree that I load from an XML file, everything works fine.但是，当我直接创建相同的子树或将其包含在从 XML 文件加载的另一棵树中时，一切正常。

How to Reproduce 如何重现

This fails: 这失败了：

#include <behaviortree_cpp/bt_factory.h>

int main(int argc, char ** argv)
{
  BT::BehaviorTreeFactory factory;
  factory.registerBehaviorTreeFromFile("/path/to/my_tree.xml");
  std::string tree_xml =
    R"(
    <root BTCPP_format="4" >
        <BehaviorTree ID="TestTree">
            <SubTree ID="MyTree"/>
        </BehaviorTree>
    </root>)";
  auto tree = factory.createTreeFromText(tree_xml);
  auto status = tree.tickWhileRunning();
  return 0;
}

This works: 这有效：

#include <behaviortree_cpp/bt_factory.h>

int main(int argc, char ** argv)
{
  BT::BehaviorTreeFactory factory;
  factory.registerBehaviorTreeFromFile("/path/to/my_tree.xml");
  auto tree = factory.createTree("MyTree");
  auto status = tree.tickWhileRunning();
  return 0;
}

It looks like it's because you didn't define SubTree, I tried to use your second way and still got the error, can you provide the /path/to/my_tree.xml?

It looks like it's because you didn't define SubTree, I tried to use your second way and still got the error, can you provide the /path/to/my_tree.xml?

Obviously this is a toy example. A definition of MyTree could look like this:

<?xml version="1.0" encoding="UTF-8"?>
<root BTCPP_format="4">
  <BehaviorTree ID="MyTree">
    <AlwaysSuccess/>
  </BehaviorTree>
</root>
``