Question

在反序列化某些JSON并尝试访问root.items后，我收到以下错误：

ServiceProvider

System.NullReferenceException：'对象引用未设置为   一个对象的实例。'

root.items @为null。

JSON如下：

 root.items.Count |> should equal 2

这是我的代码：

{
    "items": [
        {
            "snippet": {
                "title": "Nikeza: F# Backwards Pipe Operator",
                "tags": [
                    "Elm",
                    "F#",
                    "Giraffe",
                    "Functional Programming",
                    "Software Development"
                ]
            }
        },
        {
            "snippet": {
                "title": "Giraffe: VS Code bug that doesn't show up in VS 20017 (3)",
                "tags": [
                    "Hangouts On Air",
                ]
            }
        },
        {
            "snippet": {
                "title": "Software Craftsmanship Conference - London",
                "tags": [
                    "Programming",
                    "Software Development",
                ]
            }
        }
    ]
}

Answer 1

我刚刚为它编写了一个测试，我可以确认它的反序列化部分是正确的。检查请求是否正确返回响应。

open System
open Expecto

let json = 
    """
    {
        "items": [
            {
                "snippet": {
                    "title": "Nikeza: F# Backwards Pipe Operator",
                    "tags": [
                        "Elm",
                        "F#",
                        "Giraffe",
                        "Functional Programming",
                        "Software Development"
                    ]
                }
            },
            {
                "snippet": {
                    "title": "Giraffe: VS Code bug that doesn't show up in VS 20017 (3)",
                    "tags": [
                        "Hangouts On Air",
                    ]
                }
            },
            {
                "snippet": {
                    "title": "Software Craftsmanship Conference - London",
                    "tags": [
                        "Programming",
                        "Software Development",
                    ]
                }
            }
        ]
    }
    """

[<CLIMutable>]
type Snippet =    { title: string; tags: Collections.Generic.List<String> }

[<CLIMutable>]
type Item =       { snippet : Snippet }

[<CLIMutable>]
type Response =   { items : Collections.Generic.List<Item> }

[<Tests>]
let tests =
    testList "Test" [
        test "Testing deserialization" {
            let result : Response = Json.deserialize json
            Expect.equal result.items.Count 3 "Should have 3 items"
        }
    ]

Answer 2

following为我工作：

总之，我不得不求助于使用以下方法检索实际的json字符串：

json = response.Content.ReadAsStringAsync() |> Async.AwaitTask |> Async.RunSynchronously

之后，我使用了JsonConvert.DeserializeObject：

JsonConvert.DeserializeObject<Response>(json)

<强>附录

if response.IsSuccessStatusCode
    then let json = response.Content.ReadAsStringAsync() |> Async.AwaitTask |> Async.RunSynchronously
         let result = JsonConvert.DeserializeObject<Response>(json);

成功反序列化JSON后无法访问属性

2 个答案: