How to nest Futures to wait for each other in initState

Question

At first I need to fetch some ids => one of the ids returned aka: userId is used to get mailboxId => mailboxId is used to get a list of Message Models.
PS: each call is separate because this is how the API is built

@override
void initState() {
  super.initState();
  futureIds = fetchIds();
  // start those two after fetchIds() finishes
  futureMailboxId = fetchMailboxId(userId);
  futureLanguage = fetchLanguage(userId);
  // start this after fetchMailboxId(userId) finishes
  futureMessages = fetchMessages(mailboxId);
}

Solution

futureDetails: is a Future property of the StatefulWidget
Globals: contains static properties used across the app
Message: is a model with a factory method fromJson

@override
void initState() {
  super.initState();
  futureDetails = fetchIds().then((List<int> ids) => {
      Globals.userId = ids[0];
      Future.wait([
        fetchLanguage(Globals.userId),
        fetchMailboxId(Globals.userId)
      ]).then((List<dynamic> futureResult) => {
        Globals.mailboxId = futureResult[1];
        fetchMessages(Globals.mailboxId).then((Map<String, dynamic> messagesAsJson) => {
          messagesAsJson.forEach((msgJson) => Globals.messages.add(Message.fromJson(msgJson)));
        });
      });
  });
}

@override
  Widget build(BuildContext context) {
    return FutureBuilder<Widget>(
        future: futureDetails,
        builder: (BuildContext context, AsyncSnapshot<List<int>> snapshot) {
          if (snapshot.hasData) {
            // display data empty/filled
          } else if (snapshot.hasError) {
            // display error
          } else {
            // display loader
          }
        }
    );
  }