Flutter：ListView不显示任何内容+延迟加载

Question

我是 Flutter 的新手，正在尝试创建一个加载更多功能的列表视图。 这是我的课。它没有显示任何内容，空白屏幕。列表有我在控制台中得到结果的数据。

class ReportPurchaseNew extends StatefulWidget {
  final AdminUserDetails userDetails;
  final String title;

  const ReportPurchaseNew({Key key, this.title, this.userDetails})
      : super(key: key);

  @override
  State<StatefulWidget> createState() => new ReportPurchaseState();
}

class ReportPurchaseState extends State<ReportPurchaseNew> {
  String fromDate = "", toDate = "", usageType =  "";
  int limit = 7, offset = 0;
  static int page = 0;


  List<Result> _List = new List();
  List<Result> _filteredList;
  Future<PurchaseReport> _PurchaseReportResponse;
  List<UsageResult> _usageList = [];
  UsageResult _usageVal;
  ScrollController _sc = new ScrollController();
  bool isLoading = false;
  //List users = new List();

  @override
  void initState() {
    this._getMorePurchase(page);
    super.initState();
    _sc.addListener(() {
      if (_sc.position.pixels ==
          _sc.position.maxScrollExtent) {
        _getMorePurchase(page);
      }
    });

  }

  @override
  void dispose() {
    _sc.dispose();
    super.dispose();
  }

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      appBar: AppBar(
        title: const Text("Lazy Load Large List"),
      ),
      body: Container(
        child: _buildList(),
      ),
      resizeToAvoidBottomInset: false,
    );
  }

  Widget _buildList() {
    return ListView.builder(
      itemCount: _List.length + 1, // Add one more item for progress indicator
      padding: EdgeInsets.symmetric(vertical: 8.0),
      itemBuilder: (BuildContext context, int index) {
        if (index == _List.length) {
          return _buildProgressIndicator();
        } else {
          return new ListTile(
            leading: CircleAvatar(
              radius: 30.0,

            ),
            title :Text("my:"+(_List[index]
                .product)),
            subtitle: Text((_List[index]
                .unitPrice)),
          );
        }
      },
      controller: _sc,
    );
  }

  Widget _buildProgressIndicator() {
    return new Padding(
      padding: const EdgeInsets.all(8.0),
      child: new Center(
        child: new Opacity(
          opacity: isLoading ? 1.0 : 00,
          child: new CircularProgressIndicator(),
        ),
      ),
    );
  }
  Future<PurchaseReport> getProjectDetails() async {
    var result = await PurchaseReportRequest(
      context,
      widget.userDetails.result.raLoginId,
      limit.toString(),
      offset.toString(),
      fromDate,
      toDate,
      _usageVal!=null ? _usageVal.name : "" ,

    );
    return result;
  }

  void _getMorePurchase(int index) async {
    if (!isLoading) {
      setState(() {
        isLoading = true;
      });
      _PurchaseReportResponse = getProjectDetails();
      setState(() {
        isLoading = false;
        _PurchaseReportResponse.then((response) {
          if (response != null) {
            _List.addAll(response.result);
            page = page + limit;
            print("printing length : "
                +_List.length.toString());
            for (int i = 0; i < response.result.length; i++) {
              print('name:' +_List[i].product );
            }
          } else {
            errorRaisedToast(context);
          }
        });
      });
    }
  }
}

Answer 1

试试这个，

if (response != null) {
List newList = new List();
   // _List.addAll(response.result);
    page = page + limit;
    print("printing length : "
        +_List.length.toString());
    for (int i = 0; i < response.result.length; i++) {
    newList.add(response.result[i]);
      print('name:' +_List[i].product);
    }
        isLoading = false;
        _List.addAll(newList);
        page++;
     
  } else {
    errorRaisedToast(context);
  }