如何在未来的构建器(Flutter/Dart)中等待变量不等于null？

Widget build(BuildContext context) async {
  // 等待变量不为null
  await Future.delayed(Duration(seconds: 1));
  
  if (myVariable != null) {
    // 变量不为null时的处理逻辑
    return Text('Variable is not null');
  } else {
    // 变量为null时的处理逻辑
    return CircularProgressIndicator();
  }
}

Stream<int> myStream; // 假设这是一个传递变量值的流

Widget build(BuildContext context) {
  return StreamBuilder<int>(
    stream: myStream,
    builder: (BuildContext context, AsyncSnapshot<int> snapshot) {
      if (snapshot.hasData && snapshot.data != null) {
        // 变量不为null时的处理逻辑
        return Text('Variable is not null');
      } else {
        // 变量为null时的处理逻辑
        return CircularProgressIndicator();
      }
    },
  );
}