Question

我正在尝试从服务器获取 JSON 响应，并在 ListView 中输出。

以下代码导致错误：

Future<List> getCurrencies() async {
  String cryptoUrl =
      "https://pro-api.coinmarketcap.com/v1/cryptocurrency/listings/latest?CMC_PRO_API_KEY=my-key";

  http.Response response = await http.get(Uri.parse(cryptoUrl));
  return json.decode(response.body);
}

我应该返回什么以解决此错误？

我的 JSON 如下所示：

"data": [
{
"id": 1,
"name": "Bitcoin",
"symbol": "BTC",
"slug": "bitcoin",
"num_market_pairs": 8933,
"date_added": "2013-04-28T00:00:00.000Z",
"tags": [
"mineable",
"pow",
"sha-256",
"store-of-value",
"state-channels",
"coinbase-ventures-portfolio",
"three-arrows-capital-portfolio",
"polychain-capital-portfolio",
"binance-labs-portfolio",
"arrington-xrp-capital",
"blockchain-capital-portfolio",
"boostvc-portfolio",
"cms-holdings-portfolio",
"dcg-portfolio",
"dragonfly-capital-portfolio",
"electric-capital-portfolio",
"fabric-ventures-portfolio",
"framework-ventures",
"galaxy-digital-portfolio",
"huobi-capital",
"alameda-research-portfolio",
"a16z-portfolio",
"1confirmation-portfolio",
"winklevoss-capital",
"usv-portfolio",
"placeholder-ventures-portfolio",
"pantera-capital-portfolio",
"multicoin-capital-portfolio",
"paradigm-xzy-screener"
]
}

Answer 1

这是 jsonDecode 函数的原型 (它是 json.decode 的缩写)。

// dart:convert

dynamic jsonDecode(String source, {Object? Function(Object?, Object?)? reviver})

类型：动态函数(String，{Object? Function(Object?, Object?)? reviver})

它返回 dynamic。因此，getCurrencies 的适当返回类型将是

Future<dynamic> getCurrencies()

或简单地

Future getCurrencies()

jsonDecode 文档

要处理 json：

void processJson(dynamic json) {
  var x = json as Map<String, dynamic>;
  print(x['data'][0]['name']); // 打印 'Bitcoin'
}

发生了异常。_TypeError（类型'_InternalLinkedHashMap<String，dynamic>'不是'FutureOr<List<dynamic>>'的子类型）

1 个答案: