在 for 循环中等待 firestore 文档

Question

尝试在 for 循环中获取结果，但 for 循环不等待 firestore 结果。之前也尝试过 forEach。

Future<bool> checkIfNewMessages() async{
  bool hasNewMessage=false;
  QuerySnapshot _myDoc = await Firestore.instance.collection('PropMap')
      .orderBy('ProJoiningDate')
      .where('TenId', isEqualTo: globals.memberAuthId)
      .getDocuments();
  List<DocumentSnapshot> properties = _myDoc.documents;
  if(properties.length>0)
    for(final property in properties) {
    //properties.forEach((property) { //tried forEach() as well
      String propid= property.data['PropertyId'];
      
      if(property.data['LastVisitTime']!=null) {
        DateTime tenantsLastPropVisitTime = property.data['LastVisitTime'].toDate();
        
          getLastPropertyChatTime(propid).then((latestPropChatTime) { //This 'then' seems not working
           print('LAST chat date is ${latestPropChatTime}');
          if (latestPropChatTime.isAfter(tenantsLastPropVisitTime)) //This means he has not seen new messages , lets notify him
          {
            hasNewMessage= true;
          }
        });
      }
    };
  return hasNewMessage;
}

这些是 fetch 方法，当断点位于 getTheLastChat() 的 getDocuments() 时，控件只是再次跳回 for 循环而不等待结果。

Future getTheLastChat(propId) async {
  QuerySnapshot _myDoc =await Firestore.instance.collection('Chats').orderBy('ChatDate', descending: true)
      .where('PropertyId', isEqualTo: propId)
      .limit(1)
      .getDocuments();
  List<DocumentSnapshot> tenants = _myDoc.documents;
    return  tenants;    
}

Future<DateTime> getLastPropertyChatTime(propId) async {
  DateTime lastChatTime= DateTime.now().add(Duration(days:-365));
  var lastChatTimeDocs = await getTheLastChat(propId);
  lastChatTime=lastChatTimeDocs.length>0?lastChatTimeDocs[0].data["ChatDate"].toDate():DateTime.now().add(Duration(days:-365));
  return lastChatTime;
}

Answer 1

您可以使用 Future.forEach 来满足您的要求

  Future<void> buildData(AsyncSnapshot snapshot) async {
    await Future.forEach(snapshot.data.documents, (element) {
      employees.add(Employee.fromSnapshot(element));
    });
  }