NewtonSoft JSON 循环通过 JArray

Question

我正在尝试遍历 JArray，但我在 for/next 循环中收到 msg is not declared 错误。

我的 JSON 格式是这样的...

{ "messages":[
      {
        "id": 123456789,
        "sender_id": 1236547890,
        "replied_to_id": null,
        "created_at": "2017/09/28 15:49:20 +0000",
        "network_id": 554477,
        "message_type": "update",
        "sender_type": "user",
        "url": "https://www.example.com",
        "web_url": "https://www.example.com/123456789",
        "group_id": 7418529,
        "body": {
          "urls": [
            "https://www.facebook.com/blah/blah/blah",
            "https://google.com/foo/bar"
          ],
          "parsed": "Sem, imperdiet voluptatibus. Molestias, gravida vehicula, irure suscipit. Dis facilisi laudantium recusandae necessitatibus dolor quaerat quisque! Lectus deserunt taciti magnis, a non eligendi similique? Exercitationem eius corporis. Faucibus eiusmod delectus voluptatum nascetur, alias doloremque sagittis, repellendus laudantium quae, iaculis, cras maecenas fusce suspendisse amet magnam nulla gravida mollis, tempora gravida",
          "plain": "Sem, imperdiet voluptatibus. Molestias, gravida vehicula, irure suscipit. Dis facilisi laudantium recusandae necessitatibus dolor quaerat quisque! Lectus deserunt taciti magnis, a non eligendi similique? Exercitationem eius corporis. Faucibus eiusmod delectus voluptatum nascetur, alias doloremque sagittis, repellendus laudantium quae, iaculis, cras maecenas fusce suspendisse amet magnam nulla gravida mollis, tempora gravida",
          "rich": "Sem, imperdiet voluptatibus. Molestias, gravida vehicula, irure suscipit. Dis facilisi laudantium recusandae necessitatibus dolor quaerat quisque! Lectus deserunt taciti magnis, a non eligendi similique? Exercitationem eius corporis. Faucibus eiusmod delectus voluptatum nascetur, alias doloremque sagittis, repellendus laudantium quae, iaculis, cras maecenas fusce suspendisse amet magnam nulla gravida mollis, tempora gravida"
        },
        "thread_id": 956818730,
        "client_type": "Zapier",
        "client_url": "https://zapier.com/zapbook/example/",
        "system_message": false,
        "direct_message": false,
        "chat_client_sequence": null,
        "language": "en",
        "notified_user_ids": [],
        "privacy": "public",
        "attachments": [],
        "liked_by": {
          "count": 0,
          "names": []
        },
        "content_excerpt": "Sem, imperdiet voluptatibus. Molestias, gravida vehicula, irure suscipit. Dis facilisi laudantium recusandae necessitatibus dolor quaerat quisque! Lectus deserunt taciti magnis, a non eligendi similique? Exercitationem eius corporis. Faucibus eiusmod delectus voluptatum nascetur, alias doloremque sagittis, repellendus laudantium quae, iaculis, cras maecenas fusce suspendisse amet magnam nulla gravida mollis, tempora gravida",
        "group_created_id": 7418529
      },
      {
        "id": 987654321,
        "sender_id": 3214569870,
        "replied_to_id": 123555777,
        "created_at": "2017/09/28 15:28:28 +0000",
        "network_id": 554477,
        "message_type": "update",
        "sender_type": "user",
        "url": "https://www.example.com",
        "web_url": "https://www.example.com/987654321",
        "body": {
          "parsed": "Veniam quasi sem, neque netus? Eos quae voluptatibus autem optio varius euismod voluptas, voluptatum inventore",
          "plain": "Veniam quasi sem, neque netus? Eos quae voluptatibus autem optio varius euismod voluptas, voluptatum inventore",
          "rich": "Veniam quasi sem, neque netus? Eos quae voluptatibus autem optio varius euismod voluptas, voluptatum inventore"
        },
        "thread_id": 956224600,
        "client_type": "Web",
        "client_url": "https://www.example.com/",
        "system_message": false,
        "direct_message": false,
        "chat_client_sequence": null,
        "language": "en",
        "notified_user_ids": [],
        "privacy": "public",
        "attachments": [],
        "liked_by": {
          "count": 0,
          "names": []
        },
        "content_excerpt": "Veniam quasi sem, neque netus? Eos quae voluptatibus autem optio varius euismod voluptas, voluptatum inventore",
        "group_created_id": null
      }
    ]}

这是我试图用来循环 JArray 的代码...

Dim jObj As JObject = JObject.Parse(File.ReadAllText(outputJSONpath & "myFile.json"))
Dim jArr As JArray = CType(jObj("messages"), JArray)
Dim i As Int32 = 0
For Each msg As JObject In jArr 
    Dim threadID = msg.GetValue("thread_ID")
    'Do Work
Next

当我执行jArr.Count 时，它返回 6,341。为什么没有声明味精？如何获取 6,341 msg 中每个 msg 的 thread_ID 值？

Answer 1

我不确定您所说的 msg 未被声明是什么意思——它肯定是在您的 For Each 循环中声明的。听起来数组中的一个或多个消息项实际上可能是null 或不是JObject。在尝试使用它之前，您可能需要更加防御性地编写代码并检查 null 以及您得到的 JToken 的类型是否是您所期望的。与 thread_ID 值类似。也许是这样的：

For Each msg As JToken In jArr

    If Not msg Is Nothing AndAlso msg.Type = JTokenType.Object Then

        Dim threadID As JToken = msg("thread_ID")
        If Not threadID Is Nothing AndAlso threadID.Type = JTokenType.Integer Then

            Dim id As Integer = CType(threadID, Integer)

            '... Do something with id
            Console.WriteLine(id)

        End If

    End If

Next

更新

好的，我知道现在是什么问题了。当您在JToken 上使用GetValue() 或索引器语法（即msg("thread_ID")）时，属性名称区分大小写。在您的代码中，您有 thread_ID，但在 JSON 中是 thread_id，因此代码永远找不到它。

变化：

Dim threadID As JToken = msg("thread_ID")

收件人：

Dim threadID As JToken = msg("thread_id")

它应该可以工作。