如何在带有 Provider 的 ListView 中返回 Future<double>？

Posted 2023-02-23

【中文标题】如何在带有 Provider 的 ListView 中返回 Future<double>？

【英文标题】：How do I return a Future<double> in a ListView with Provider?

【发布时间】：2020-12-27 21:57:51

【问题描述】：

我正在尝试使用 Provider 包将 Future 放入列表视图，但没有成功。谁能给我一些建议或链接来解释如何在返回双精度的 Future 上实现 notifylisteners()？

这是 getPrice() 的未来：

import 'dart:collection';
import 'package:http/http.dart' as http;
import 'package:flutter/material.dart';
import 'package:stock_watchlist/stock_service.dart';

class StockData extends ChangeNotifier 
  List<Stock> _stocks = [
    Stock(symbol: 'AAPL'),
    Stock(symbol: 'AMD'),
    Stock(symbol: 'TSLA')
  ];

  UnmodifiableListView<Stock> get stocks 
    return UnmodifiableListView(_stocks);
  

  int get stockCount 
    return _stocks.length;
  

  void addStock(String symbol, double price, double eps) 
    final stock = Stock(symbol: symbol);
    _stocks.add(stock);
    notifyListeners();
  

  void deleteStock(Stock stock) 
    _stocks.remove(stock);
    notifyListeners();
  

  Future<double> getPrice(String symbol) async 
    String url =
        "https://sandbox.iexapis.com/stable/stock/$symbol/quote/latestPrice?token=Tsk_38ddda0b877a4510b42a37ae713cdc96";

    http.Response response = await http.get(url);
    double price = double.tryParse(response.body);
    return price;
  

  Future<double> getEps(String symbol) async 
    String url =
        "https://sandbox.iexapis.com/stable/stock/$symbol/stats/ttmEPS?token=Tsk_38ddda0b877a4510b42a37ae713cdc96";

    http.Response response = await http.get(url);
    double eps = double.tryParse(response.body);
    return eps;
  

这是我尝试将 getPrice() 的值输入到文本小部件的地方，但它给了我“'Future' 的实例而不是值。

I cannot embed pictures yet

import 'package:flutter/material.dart';
import 'package:provider/provider.dart';
import 'package:stock_watchlist/constants.dart';
import 'package:stock_watchlist/stock_model.dart';

class StockList extends StatelessWidget 
  @override
  Widget build(BuildContext context) 
    return Consumer<StockData>(
      builder: (context, stockData, child) 
        return ListView.builder(
          itemCount: stockData.stockCount,
          itemBuilder: (context, index) 
            //
            final stockIndex = stockData.stocks[index];
            //
            return ListTile(
              title: Text(
                stockIndex.symbol,
                style: TextStyle(
                  color: kTextColor,
                ),
              ),
              subtitle: Text(
                stockIndex.price.toString(),
                style: TextStyle(
                  color: kTextColor,
                ),
              ),
            );
          ,
        );
      ,
    );
  

【问题讨论】：

你试过FutureBuilder吗？您可以尝试使构建器功能async 然后final stockIndex = await stockData.stocks[index]。

【参考方案1】：

谢谢，我想我是用 FutureBuilder 解决的。这是我使用的代码。

class StockList extends StatelessWidget 
  @override
  Widget build(BuildContext context) 
    return Consumer<StockData>(
      builder: (context, stockData, child) 
        return ListView.builder(
          itemCount: stockData.stockCount,
          itemBuilder: (context, index) 
            //
            final stockIndex = stockData.stocks[index];
            //
            return ListTile(
              title: Text(
                stockIndex.symbol,
                style: TextStyle(
                  color: kTextColor,
                ),
              ),
              subtitle: FutureBuilder(
                future: stockData.getPrice(stockIndex.symbol),
                builder: (context, snapshot) => Text(
                  snapshot.data.toString(),
                  style: TextStyle(
                    color: kTextColor,
                  ),
                ),
              ),
            );
          ,
        );
      ,
    );