为什么 JsonConvert.DeserializeObject 返回错误：异常：值不能为空。(参数"源")

Question

我有一个public async Task GetCompaniesAsync()，编码如下：

public async Task GetCompaniesAsync()
{
_getCompaniesSuccessful = false;
var result = await _http.GetAsync($"https://somesite.com/api/companies");
if (result.IsSuccessStatusCode)
{
// I split the code after the suggestion of @mjwills (thanks)
var content = await result.Content.ReadAsStringAsync();
var obj = JsonConvert.DeserializeObject<StockMarket>(content).Companies;
// at this point, content.Length has a value (e.g. 24429)
// but, obj is null (after JsonConvert)
if (obj != null)
{
_companies = obj.ToList();
_getCompaniesSuccessful = true;
}
}

在其他类中，我使用以下代码：

await MyService.GetCompaniesAsync();

if (MyService.GetCompaniesSuccessful)
{
foreach (var record in MyService.Companies)
{
await Context.Channel.SendMessageAsync($"{record.TickerSymbol,-10}t{record.CompanyName,-10}");
}
}

但当我得到以下错误时：异常：值不能为null。(参数'source')可能是它还没有完成数据检索吗？请帮忙。。。

顺便说一下，webapi url返回JSON数据，它看起来像这样：

{
"companies": [
{
"ticker": "HEY",
"name": "Hey Corporation",
"status": "open"
},
{
"ticker": "PER",
"name": "Pears Corporation",
"status": "close"
},
{
"ticker": "BRGR",
"name": "Burger Inc.",
"status": "open"
},
]
}           

这些是股票市场和公司类别：

public class StockMarket
{
public StockMarket()
{
}
public ICollection<Company> Companies { get; set; }
}
public class Company
{
public Company()
{
TickerSymbol = "";
CompanyName = "";
Status = "";
}
public string TickerSymbol { get; set; }
public string CompanyName { get; set; }
public string Status { get; set; }
}

Answer 1

查看示例，您的JSON有一个"name"；键，但是您的Company类的属性被称为"；公司名称">

尝试将属性更改为简单的名称，或使用此进行装饰

[JsonProperty("名称"，NullValueHandling=NullValueHandler.Ignore)]

此外，TickerSymbol属性也是如此。