从Flutter中的快照创建自己的流列表

问题描述

背景：我正在开发一个 Flutter应用，该应用可以跟踪房租付款。我得到了一个列表，列出了租户尚未支付租金的月份（dueMonths），代码如下。

问题： 我受困的地方是，快照{}之后快照中的付款清单为空，但值在{}内部。如果Payments集合中有任何更改，则列表不会更新。

我想实现什么？ 当用户付款时，我希望快照更新付款清单，然后更新notifyList（必须从该清单中删除月份）。我无法完成这项工作，并且浪费了过去两天的时间。请帮助我。

Stream<List> getnopaymentList() {

StreamController<List> controller = new StreamController<List>();   //Add .broadcast here

// list of units rented by the tenant. He has rented 4A and G3
List units = [
  {'unitId': '4hFIcmbKhJgyrppsTBOc','unitName': '4A','propertyId': 'YF5k6D2abFsczVxSmLZu','rent': 6000},{'unitId': 'zDyCfrFYnsHIE2nAuP7B','unitName': 'G3','propertyId': 'IDroypXJyzMIb7a6jUqH','rent': 6000}
];
// checking the payments for the past three months
List dueMonths = ['2020-07','2020-06','2020-05'];
List payments = [];
List notifyList = [];

//document id of the user
String currentUid = 'kEamSzzDt4Yb9PgPGCg8AxDPrrp2';

//get list of payments done by the tenant for the due months
Stream<QuerySnapshot> paymentSS = Firestore.instance.collection('payment')
    .where('paid_for',whereIn: dueMonths)
    .where('tenant_id',isEqualTo: currentUid)
    .snapshots();
paymentSS.forEach((snapshot) {
  snapshot.documents.forEach((doc) {  //when there is a change in docs,this is working and payments list is added. notifyList is not updated.
    payments.add(
        {'unitId': doc.data['unit_id'],'paidFor': doc.data['paid_for']}
    );
  });
});
// payments list is EMPTY outside the loop
units.forEach((unit) {
  dueMonths.forEach((month) {
    bool paid = false;
    payments.forEach((pay) {print('no pay');
      if(unit['unitId'] == pay['unitId'] && month == pay['paidFor']){
        paid = true;
      }
    });
    if(paid == false){
      notifyList.add({
        'unitId' : unit['unitId'],'unitName' : unit['unitName'],'propertyId' : unit['propertyId'],'rent' : unit['rent'],'notPaidFor' : month
      });
    }
  });
});

controller.sink.add(notifyList);
return controller.stream;

}

我正在使用以下代码收听流

                StreamBuilder(
                  stream: NotificationService().getnopaymentList(),builder: (context,snapshot) {
                    if(!snapshot.hasData){
                      return Text('Loading...');
                    }
                    var data = snapshot.data;
                    //print(data);
                    //print('status is'+ snapshot.connectionState.toString());
                    return Text('Stream Here');
                  },),

解决方法

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dart google-cloud-firestore snapshot