我想用StreamBuilder结果实时更改应用栏图标（操作），
我用这个方法

class MyApp extends StatefulWidget {
  @override
  _MyAppState createState() => _MyAppState();
}

class _MyAppState extends State<MyApp> {
  bool isOk = false;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        actions: [
          IconButton(
              onPressed: () {},
              icon: isOk ? Icon(Icons.edit) : Icon(Icons.edit_off))
        ],
      ),
      body: StreamBuilder(
        stream: FirebaseFirestore.instance
            .collection("users")
            .doc(FirebaseAuth.instance.currentUser!.uid)
            .snapshots(),
        builder: (context, streamSnapshot) {
           // set this -------------------------------------------------------
           if (streamSnapshot.data!['newRequests'].length != 0) {
             setState(() {
               isOk = true;
             });
           }
           //---------------------------------------------------------------------
          return Center(
              child: CustomText(
            size: 60,
            text: streamSnapshot.data!['newRequests'].length != 0 ? "Have" : "0",
            textColor: darkblueColor,
          ));
        },
      ),
    );
  }
}

它不起作用。它显示如下错误：

════════ Exception caught by widgets library ═══════════════════════════════════
setState() or markNeedsBuild() called during build.
The relevant error-causing widget was
StreamBuilder<DocumentSnapshot<Map<String, dynamic>>>