使用 C# 并使用 foreach 从 JSON 字符串中获取二级值

Question

完整的 JSON 新手 - 这是我第一次使用 C# 进入 JSON。

我有一条从 HTTP 获取请求返回的记录。

var exchRateData = Get($"https://api.exchangeratesapi.io/2018-10-30?base=EUR&symbols=AUD");

返回： {"date":"2018-10-30","rates":{"AUD":1.6025},"base":"EUR"}.

AUD 和 1.6025 值都是 GET 请求中的变量。因此 GET 请求可以针对它返回的 SGD 或 INR：

{"date":"2018-10-30","rates":{"SGD":0.0187977737},"base":"INR"}

总是返回一个带有级别的记录，就像上面的两个示例一样。

我想要的是访问二级值的值，

即{"AUD":1.6025} or {"SGD":0.0187977737}

我试过了：

var jsonResult = JsonConvert.DeserializeObject<Dictionary<string, dynamic>>(exchRateData);
                    foreach (var keyValue in jsonResult)
                {
                    try
                    {
                        LblGetValues.Text = LblGetValues.Text + "Key: " + keyValue.Key + " Value:" + keyValue.Value + "<br>";
                        if (keyValue.Key == "date")
                            LblDate.Text = keyValue.Value;

//This is where I get stuck.
                        if (keyValue.Key == "rates")
                        {
// I would like to be able to do this here : 
//string currencyCode =  "AUD" (or "SGD" if second GET request)
//double currencyRate = 1.6025  (or 0.0187977737 if second GET request)
                            //JArray secondLevel = new JArray("rates");

                         //   LblRate.Text = keyValue.Value.ToString();

                        }

                        if (keyValue.Key == "base")
                            LblBase.Text = keyValue.Value;
                    }
                    catch (Exception errMsg)
                    {
                        LblMsg.Text = errMsg.Message + errMsg.StackTrace;
                    }
                }

请帮忙....

Answer 1

我建议使用JSON.NET

在这里您将把您的 JSON 字符串反序列化到您的 c# 模型类中

您的模型类将如下所示Model Generated using json2csharp

public class Rates
{
    [JsonProperty(PropertyName = "fieldName")]
    public double currency { get; set; }
}

public class RootObject
{
    public string date { get; set; }
    public Rates rates { get; set; }
    public string @base { get; set; }
}

那么这就是你使用 JSON.NET 反序列化它的方式

// THis works for normal secanario but it won't work for you 
var exchangeRates = JsonConvert.DeserializeObject<RootObject>("Your Json String goes here");

但是你的 JSON 场景有点复杂，所以你必须使用 自定义合约解析器

这是一个例子

ContractResolver 类

internal class CustomContractResolver : DefaultContractResolver
{
    public CustomContractResolver(string fieldName)
    {
        FieldName = fieldName;
    }

    public string FieldName { get; set; }

    protected override string ResolvePropertyName(string propertyName)
    {
        return propertyName == "fieldName" ? FieldName : base.ResolvePropertyName(propertyName);
    }
}

如何使用此设置

var settings = new JsonSerializerSettings
{
    DefaultValueHandling = DefaultValueHandling.Ignore,
    MissingMemberHandling = MissingMemberHandling.Ignore,
    ContractResolver = new CustomContractResolver("Pass Your currency here")
};

// Make Http Calls here and replace returned string in below method

var data = JsonConvert.DeserializeObject<RootObject>("Your JSON String", setting);
// Here You can access your currency rates
double currencyRate = data.currency;

Answer 2

   public class Rates
    {
        public double AUD { get; set; }
    }

    public class ObjectCurrency
    {
        public string date { get; set; }
        public Rates rates { get; set; }
        public string @base { get; set; }
    }


  var data= JsonConvert.DeserializeObject<ObjectCurrency>(exchRateData);

Answer 3

如果只有一个费率（这是 OP 想要的），则接受的解决方案可以正常工作，但它不适用于超过 1 个费率。此外，它增加了额外的复杂性，这可以通过使用 Dictionary 来避免（见下文）。

示例 - 以下请求（AUD、USD、GBP）

https://api.exchangeratesapi.io/2018-10-30?base=EUR&symbols=AUD,USD,GBP

将返回以下 json：

{"date":"2018-10-30","rates":{"USD":1.1372,"GBP":0.89148,"AUD":1.6025},"base":"EUR"}

您可以使用以下 C# 类来反序列化您的 json 字符串：

public class ExchangeRate
{
    [JsonProperty("date")]
    public string Date { get; set; }

    [JsonProperty("rates")]
    public Dictionary<string, decimal> Rate { get; set; }

    [JsonProperty("base")]
    public string Base { get; set; }
}

反序列化json字符串：

string json = @"{""date"":""2018-10-30"",""rates"":{""USD"":1.1372,""GBP"":0.89148,""AUD"":1.6025},""base"":""EUR""}";

ExchangeRate rate = JsonConvert.DeserializeObject<ExchangeRate>(json);

结果：