Flutter - StreamProvider - 发送重复的XHR请求到Firebase。

Question

我注意到，自从我使用下面的命令添加了一个新的流之后，我的读取请求显著增加了。StreamProvider，我设法确认这一点，通过删除流和没有重复请求的地方。但我似乎无法追踪它为什么会重复。

注意：代码功能正常，只是这些读取请求已经到了屋顶。

流

//get list of all open enquiries
  Stream<List<EnquiryData>> get centreDashboardOpenEnquiries {
    return centresCollection.document(centreID).collection('enquiries').where('enquiryStatus', whereIn: ['New', 'Contacted', 'Tour Scheduled', 'Tour Completed']).snapshots().map(_enquiryList);
  }

  //Map QuerySnapshot to List of EnquiryData
  List<EnquiryData> _enquiryList(QuerySnapshot enquiry){
    return enquiry.documents.map((doc) {
      return EnquiryData(
        enquiryID: doc.data['enquiryID'].toString(),
        parentFirstName: doc.data['firstName'],
        parentLastName: doc.data['lastName'],
        parentPhoneNumber: doc.data['phoneNumber'],
        parentEmail: doc.data['email'],
        parentAddress: doc.data['address'],
        methodOfEnquiry: doc.data['methodOfEnquiry'],
        hearAboutUs: doc.data['hearAboutUs'],
        specificHearAboutUs: doc.data['specificHearAboutUs'],
        impressionOfCentre: doc.data['firstImpression'],
        enquiryStatus: doc.data['enquiryStatus'],
        created: doc.data['created'],
        lastUpdated: doc.data['lastUpdated'],
      );
    }).toList();
  }

调用流与CurrentOpenDataTable子表

child: StreamProvider<List<EnquiryData>>.value(
    value: EnquiryDatabaseService(centreID: widget.centreData.centreID).centreDashboardOpenEnquiries,
    child: CurrentOpenDataTable(),
),

当前打开的数据表()

class CurrentOpenDataTable extends StatefulWidget {
  @override
  _CurrentOpenDataTableState createState() => _CurrentOpenDataTableState();
}

class _CurrentOpenDataTableState extends State<CurrentOpenDataTable> {
  @override
  Widget build(BuildContext context) {
    final enquiryData = Provider.of<List<EnquiryData>>(context) ?? [];
    return DataTable(
      showCheckboxColumn: false,
      sortColumnIndex: 1,
      sortAscending: true,
      columns: [
        DataColumn(
          label: Text('Date'),
        ),
        DataColumn(
          label: Text('Name'),
          //numeric: true,
        ),
        DataColumn(
          label: Text('Status'),
        ),
      ],
      rows: _enquiryRow(context, enquiryData),
    );
  }
}

_dateFormat(DateTime dateTime) {
  String formattedDate = DateFormat('dd/MM/yyyy').format(dateTime);
  return formattedDate;
}

_enquiryRow(BuildContext context, List<EnquiryData> enquiryData) {
  List<DataRow> listOfDataRows = List.generate(
      enquiryData.length,
      (index) => DataRow(
              cells: [
                DataCell(Text(_dateFormat(DateTime.fromMillisecondsSinceEpoch(
                    enquiryData[index].created)))),
                DataCell(Text(enquiryData[index].parentFirstName +
                    ' ' +
                    enquiryData[index].parentLastName)),
                DataCell(Text(enquiryData[index].enquiryStatus)),
              ],
              onSelectChanged: (bool selected) {
                if (selected) {
                  showEnquiryDialog(context, enquiryData[index]);
                }
              }));
  return listOfDataRows;
}

Answer 1

小部件（让我们称它为 MyWidget)，其中包含 StreamProvider 正在不断重建。

你不应该创建 EnquiryDatabaseService 里面 StreamProvider<List<EnquiryData>>.value，而不是在 initState.

例子

class _MyWidgetState extends State<MyWidget> {
  Stream<List<EnquiryData>> _stream;

  @override
  initState() {
    _stream = EnquiryDatabaseService(centreID: widget.centreData.centreID). centreDashboardOpenEnquiries;
  }

  // ... in build
  StreamProvider.value(
    value: _stream,
    child: Container(/* ... */),
  ),
}

或者不要使用 .value 构造函数。

StreamProvider(
  create: (_) => EnquiryDatabaseService(centreID: widget.centreData.centreID). centreDashboardOpenEnquiries,
  child: Container(/* ... */),
),

阅读更多关于 这里的做法和不做法更多参考资料请点击这里 - 如何处理不需要的小部件构建？