Question

我根据用户提供的预订号码从我的ASP.NET Web API请求预订信息。我的问题是，如果预订编号不存在，Web API仍然返回一个对象，但值为null。如何检查返回的JSON对象是否为null？

HttpClient请求：

 var response = await client.PostAsJsonAsync(strRequestUri, value);

if (response.IsSuccessStatusCode)
{
    string jsonMessage;
    using (Stream responseStream = await response.Content.ReadAsStreamAsync()) // put response content to stream
    {
        jsonMessage = new StreamReader(responseStream).ReadToEnd(); 
    }
    // I'm getting the error from here when I'm casting the json object to my return type.
    return (TOutput)JsonConvert.DeserializeObject(jsonMessage, typeof(TOutput)); // TOutput is a generic object
}

示例返回JSON对象：

{
    "BookingRef": null,
    "City": null,
    "Company": null,
    "Country": null,
    "CustomerAddress": null,
    "CustomerFirstName": null,
    "CustomerPhoneNumber": null,
    "CustomerSurname": null,
    "Entrance": null
}

Answer 1

一种选择是在属性上使用后期绑定：

var result = JsonConvert.DeserializeObject(jsonMessage, typeof(TOutput));
if (((dynamic)result).BookingRef == null)
{
    // Returning null - do whatever is appropriate
    return null;
}
else
{
    return (TOutput)result;
}

无效对象无法转换为值类型

1 个答案: