在颤振中从 JSON 中获取数据答案

【问题标题】：Get data from JSON in flutter在颤振中从 JSON 中获取数据
【发布时间】：2021-03-26 06:13:26
【问题描述】：

我正在使用以下代码来验证股票数据：

Future<Stock> verifyIfStockSymbolIsValid(String symbol) async {
  final response =
  await http.get('https://cloud.iexapis.com/stable/stock/$symbol/quote?token=my-token');
  if (response.statusCode == 200) {
    // Get Map from JSON.
    Map data = json.decode(response.body);
    print(data); // here the data (output below) is printed!

    Map quoteData = data['quote'];
    Stock stockQuote = Stock.fromJson(quoteData); // here should be the problem
 
    return stockQuote;
  } else {
    return null;
  }
}

输出如下：

I/flutter (9290): {symbol: XOM, companyName: Exxon Mobil Corp., primaryExchange: NEW YORK STOCK EXCHANGE, INC., calculatePrice: tops, open: null, openTime: null, openSource: official, close: null, closeTime: null, closeSource: 官方, high: null, highTime: 1608044090030, highSource: 15分钟延迟价格, low: null, lowTime: 1608044281245, lowSource: IEX实时价格, latestPrice: 42.52, latestSource: IEX实时价格, latestTime: 10:09:34 AM, latestUpdate: 1608044974460, latestVolume: null, iexRealtimePrice: 42.52, iexRealtimeSize: 100, iexLastUpdated: 1608044974460, delayedPrice: null, delayedPriceTime: null,oddLotDelayedPrice: null,oddLotDelayedPriceTime: null, extendedP extendedChange：null，extendedChangePercent：null，extendedPriceTime：null，previousClose：42.22，previousVolume：30595042，change：0.3，changePercent：0.00711，volume：null，iexMarketPercent：0.01788127392568208，iexVolume：65063，avgTotalVolume：306838479，iexBidPriceS：：100，iexAskPrice：42.51，iexAskSize：400，iexOpen：42.475，iexOpenTime：1608052428625，iexClose：42.475，iexCloseTime：1608052428625，marketCap：179594243992，操作：54.63，week52High：65.66，week52Low：29.54，ytdChange：-0.3405948289133432，lastTradeTime： 1608052428625, isUSMarketOpen: true}
E/flutter（9290）：[错误：flutter/lib/ui/ui_dart_state.cc（177）]未处理的异常：NoSuchMethodError：方法'[]'在null上被调用。
E/颤振（9290）：接收器：空
E/flutter（9290）：尝试调用：

我的股票类是这样的：

class Stock {

  final String companyName;
  final String symbol;

  // The following are dynamic as using double generates an error
  // when the API returns values with no decimal (e.g. 12 vs 12.0).
  final dynamic latestPrice;
  final dynamic low;
  final dynamic high;
  final dynamic week52High;
  final dynamic change;
  final dynamic changePercent;
  final dynamic peRatio;
  final dynamic previousClose;

  // Default constructor.
  Stock(this.companyName, this.symbol, this.latestPrice,
  this.low, this.high, this.week52High, this.change,
  this.changePercent, this.peRatio, this.previousClose);

  // Named constructor, create object from JSON.
  Stock.fromJson(Map<String, dynamic> json)
  : companyName = (json['companyName'] != null ? json['companyName'] : ""),
    symbol = (json['symbol'] != null ? json['symbol'] : ""),
    latestPrice = (json['latestPrice'] != null ? json['latestPrice'] : 0.0),
    low = (json['low'] != null ? json['low'] : 0.0),
    high = (json['high'] != null ? json['high'] : 0.0),
    week52High = (json['week52High'] != null ? json['week52High'] : 0.0),
    change = (json['change'] != null ? json['change'] : 0.0),
    changePercent = (json['changePercent'] != null ? json['changePercent'] : 0.0),
    peRatio = (json['peRatio'] != null ? json['peRatio'] : 0.0),
    previousClose = (json['previousClose'] != null ? json['previousClose'] : 0.0);
}

我该如何解决这个问题？

【问题讨论】：

请分享您的整个 JSON，您提供的输出已被剪切，因为打印方法有限制。通过使用调试模式并在分配变量后立即设置断点，您可以轻松获取整个变量内容。
我编辑了输出！
data['quote'] 不是一个东西，因此，它是null。

标签： json flutter dart fromjson

【解决方案1】：

final data = json.decode(response.body) as Map;

print(data); // here the data (output below) is printed!

final  quoteData = data['quote'] as Map;

铸造是小鬼，试试这个，也让我知道.. 只替换上面的 3 行

【讨论】：