list - 如何将我的数据保存在列表中，以便在Flutter应用程序的整个生命周期中都可以使用？

Question

在我的flutter应用程序中，我正在使用具有清晰体系结构的mvp，当我的服务器命中api时，我的服务器返回5个项目，当我再次滚动它时，再次命中api并获得了下5个项目。而且我将这些项目保存在列表中，这样我就无法为已经获取的项目一次又一次地调用api，并且此列表已在listview.builder中使用。我使用了底部导航栏，当我从“产品项”选项卡移至任何其他选项卡，并且从那里来到产品项时，它再次从api获取产品，这不是我想要的。每当我返回时，我想在产品列表选项卡中显示该列表已获取的列表。
Video of my problem。

import 'dart:async';

import 'package:bakery_application/Bloc/TECartBloc.dart';
import 'package:bakery_application/Singleton/CartManager.dart';
import 'package:bakery_application/data/dataSource/product/remote/ProductRemoteDataSource.dart';
import 'package:bakery_application/data/model/responseDTO/ProductResponseDTO.dart';
import 'package:bakery_application/data/model/responseDTO/models/products.dart';
import 'package:bakery_application/data/model/responseDTO/models/productsList.dart';
import 'package:bakery_application/domain/repository/product/ProductRepo.dart';
import 'package:bakery_application/ui/productdetailscreeen/ProductDetailScreen.dart';
import 'package:bakery_application/ui/productscreen/IProductPresenter.dart';
import 'package:bakery_application/ui/productscreen/IProductView.dart';
import 'package:connectivity/connectivity.dart';
import 'package:flutter/cupertino.dart';
import 'package:flutter/material.dart';
import 'package:bakery_application/localmodels/ProductModel.dart';
import 'package:bakery_application/widgets/TEProductIncrementor.dart';
import 'package:modal_progress_hud/modal_progress_hud.dart';
import 'package:provider/provider.dart';

import 'ProductPresenter.dart';

class ProductScreen extends StatefulWidget {
  Key key;
  List<Products> myList = new List<Products>();
  int _pageNumber = 1;
  ProductScreen({
    this.key,
  }) : super(key: key);
  @override
  _ProductScreenState createState() => _ProductScreenState();
}

class _ProductScreenState extends State<ProductScreen> implements IProductView {
  _ProductScreenState() {
    productPresenter = ProductPresenter(
      this,
      ProductRepo(
        ProductRemoteDataSource(),
      ),
    );
  }

  bool circularindicator = false;
  Color circularColor;
  double circularOpacity;
  IProductPresenter productPresenter;
  AsyncSnapshot snapshotList;
  var _connectionStatus = 'Unknown';
  Connectivity connectivity;
  StreamSubscription<ConnectivityResult> subscription;
  ScrollController _scrollController = ScrollController();
  bool cupertinoProgress;

  @override
  Widget build(BuildContext context) {
    return Scaffold(
      backgroundColor: Colors.white,
      appBar: AppBar(
        backgroundColor: Colors.orange,
        automaticallyImplyLeading: false,
        title: Text(
          'Product',
          style: TextStyle(color: Colors.white),
        ),
      ),
      body:
          StreamBuilder(
        stream: productPresenter.getProducts,

        builder: (context, AsyncSnapshot<ProductsList> snapshot) {
          if (snapshot.hasData) {
            return productListView(widget.myList);
          } else if (snapshot.hasError) {
            return Text(snapshot.error.toString());
          }
          return Center(
            child: Container(
              child: CircularProgressIndicator(),
            ),
          );
        },
      ),
    );

  }

  Future<Null> refreshList() async {
    await Future.delayed(Duration(seconds: 2));
    setState(() {});

    return null;
  }

  Widget productListView(List snapshot) {
    return RefreshIndicator(
      onRefresh: refreshList,
      child:
          ListView.builder(
        key: widget.key,
        controller: _scrollController,
        shrinkWrap: true,
        scrollDirection: Axis.vertical,
        itemBuilder: (BuildContext context, int index) {


          if(index+1 == widget.myList.length) {
            CupertinoActivityIndicator();
          }

          var plist = widget.myList[index];
          return GestureDetector(
            onTap: () => Navigator.push(
              context,
              MaterialPageRoute(
                builder: (context) => ProductDetailScreen(
                  product: plist,
                ),
              ),
            ),
            child: Padding(
              padding: const EdgeInsets.all(8.0),
              child: Column(
                children: <Widget>[
                  Row(
                    mainAxisAlignment: MainAxisAlignment.start,
                    crossAxisAlignment: CrossAxisAlignment.start,
                    children: <Widget>[
                      Container(
                        width: 120,
                        height: 130,
                        child: Image(
                          image: NetworkImage(plist.image),
                        ),
                      ),
                      Container(
                        child: Flexible(
                          child: Padding(
                            padding: const EdgeInsets.all(8.0),
                            child: Column(
                              mainAxisAlignment: MainAxisAlignment.start,
                              crossAxisAlignment: CrossAxisAlignment.stretch,
                              children: <Widget>[
                                Text(
                                  plist.name,
                                  style: TextStyle(
                                    fontWeight: FontWeight.bold,
                                    fontSize: 16,
                                  ),
                                ),
                                Text(
                                  plist.description,
                                  softWrap: true,
                                  textAlign: TextAlign.left,
                                ),
                                SizedBox(
                                  height: 7,
                                ),
                                Row(
                                  children: <Widget>[
                                    Text(plist.price.toString(),
                                        style: TextStyle(
                                          fontWeight: FontWeight.bold,
                                          fontSize: 20,
                                        )),
                                    Spacer(),
                                    Text(plist.brand),
                                  ],
                                ),
                                TEProductIncrementor(
                                  product: plist,
                                ),
                                //TODO reverse it alse
                              ],
                            ),
                          ),
                        ),
                      ),
                    ],
                  ),
                  Row(
                    children: <Widget>[
                      Expanded(
                        child: Divider(
                          color: Colors.grey.shade300,
                        ),
                      ),
                    ],
                  )
                ],
              ),
            ),
          );
        },
        itemCount: widget.myList.length,
      ),
    );
  }

  productlist(BuildContext context, int index

  }

  @override
  hideProgress(ProductsList response) {

      setState(() {
        // Here you can write your code for open new view
        cupertinoProgress=false;
      });
    for (var c in response.products) {
      widget.myList.add(c);
    }
  }

  @override
  showError(String error) {
    // TODO: implement showError
    return null;
  }

  @override
  showProgress() {
    print('Successful');
    setState(() {
      cupertinoProgress=true;
    });
  }

  @override
  void initState() {
    super.initState();
    connectivity = new Connectivity();
    print('Init state called');
    print('Init state called');
    print('Init state called');
    subscription =
        connectivity.onConnectivityChanged.listen((ConnectivityResult result) {
      _connectionStatus = result.toString();
      print(_connectionStatus);
      if (result == ConnectivityResult.wifi ||
          result == ConnectivityResult.mobile) {
        widget.myList.isEmpty
            ? productPresenter.fetchProducts(widget._pageNumber.toString())
            :
                widget._pageNumber = widget._pageNumber + 1;
                productPresenter.fetchProducts(widget._pageNumber.toString(),);

        _scrollController.addListener(() {
          if (_scrollController.position.pixels ==
              _scrollController.position.maxScrollExtent) {
            widget._pageNumber = widget._pageNumber + 1;
            print(widget._pageNumber);
            productPresenter.fetchProducts(widget._pageNumber.toString(),);
          }
        });
      } else {
        showDialog(
          context: context,
          builder: (context) {
            return AlertDialog(
              title: Center(
                child: Container(
                  child: Icon(
                    Icons.add_alert,
                    color: Colors.orange,
                    size: 20,
                  ),
                ),
              ),
              content: Text('Check your internet'),
              actions: <Widget>[
                new FlatButton(
                  child: new Text('Ok'),
                  onPressed: () {
                    Navigator.of(context).pop();
                  },
                ),
              ],
            );
          },
        );
      }
    });
  }

  @override
  void dispose() {
    subscription.cancel();
    super.dispose();
  }

  getMoreData() async {
  }

}

Answer 1

您面临的主要问题是，每当用户滚动您所在的标签页并返回该标签页时，该应用程序都会重新获取数据。

您可以使用IndexedStack使数据仅加载一次，因为您可以通过这种方式编辑代码。

class BaseScreenState extends State<BaseScreen> {

   List<Widget> _pages = [Page1(), Page2(), Page3()];

   @override
   Widget build(BuildContext context) {
      return Scaffold(
         body: IndexedStack(
                index: currentIndex,
                children: _pages,
               ),
      );
   }
}