flutter - Stream tree view data to List<TreeViewNode>

Question

I keep tree view data on my firebase. I am receiving this data as a stream. The data is kept in firebase with the ProductCategory model. Within the ProdutCategory model, children data is kept as Stream. I need to convert this data to List . I wrote the following codes for this. However, although it works, it cannot notice the changes in children and works very slowly.

I'm waiting for your suggestions, thank you

Future<List<TreeViewNode>> transform(
  Stream<List<ProductCategory>> streamLPC) async {
List<ProductCategory> lp = await streamLPC.first;
List<TreeViewNode> lt = [];
for (var i = 0; i < lp.length; i++) {
  ProductCategory p = lp[i];
  List<TreeViewNode> ct = [];
  if (p.childProductCategories != null) {
    ct = await transform(p.childProductCategories);
  }
  TreeViewNode t = TreeViewNode(
    key: p.id,
    label: p.name,
    children: ct,
  );
  lt.add(t);
}
return lt;
}

Stream<List<TreeViewNode>> getStreamTreeViewNodeList(
  Stream<List<ProductCategory>> streamProductCategoryList) {
StreamTransformer streamTransformer = StreamTransformer<
        List<ProductCategory>, List<TreeViewNode>>.fromHandlers(
    handleData: (List<ProductCategory> listPC,
        EventSink<List<TreeViewNode>> listTN) async {
  List<TreeViewNode> lt = [];
  for (var i = 0; i < listPC.length; i++) {
    List<TreeViewNode> c =
        await transform(listPC[i].childProductCategories);
    ProductCategory p = listPC[i];
    TreeViewNode t = TreeViewNode(key: p.id, label: p.name, children: c);
    lt.add(t);
  }
  listTN.add(lt);
});
return streamProductCategoryList.transform(streamTransformer);
}

Answer 1

等待大神答复