Visual Basic 获取 Json 值

Question

我正在制作一个应用程序，我需要从 json 文件中读取某个值。

json文件格式如下...

{
  "files": [
    {
      "id": [
        6856,
        3667
      ],
      "uid": 15749645081288,
      "file_id": 6856,
      "name": "Name",
      "version": "001",
      "category_id": 4,
      "category_name": "OLD_VERSION",
      "is_primary": false,
      "size": 4,
      "file_name": "Name_001-1539-001-1633022640.zip",
      "uploaded_timestamp": 1633022640,
      "uploaded_time": "2021-09-30T17:24:00.000+00:00",
      "mod_version": "001",
      "external_virus_scan_url": "https://www.virustotal.com",
      "description": "Version 001 Public",
      "size_kb": 4,
      "size_in_bytes": 3961,
      "changelog_html": "Public",
      "content_preview_link": "URL"
    },
    {
      "id": [
        6872,
        3667
      ],
      "uid": 15749645081304,
      "file_id": 6872,
      "name": "Name_002",
      "version": "002",
      "category_id": 1,
      "category_name": "MAIN",
      "is_primary": true,
      "size": 4,
      "file_name": "Name_002-1539-002-1633106391.zip",
      "uploaded_timestamp": 1633106391,
      "uploaded_time": "2021-10-01T16:39:51.000+00:00",
      "mod_version": "002",
      "external_virus_scan_url": "https://www.virustotal.com/",
      "description": "Update 002 . See changelog.",
      "size_kb": 4,
      "size_in_bytes": 4150,
      "changelog_html": "Stuff",
      "content_preview_link": "URL"
    }
  ],
  "file_updates": [
    {
      "old_file_id": 6856,
      "new_file_id": 6872,
      "old_file_name": "Name_001-1539-001-1633022640.zip",
      "new_file_name": "Name_002-1539-002-1633106391.zip",
      "uploaded_timestamp": 1633106392,
      "uploaded_time": "2021-10-01T16:39:52.000+00:00"
    }
  ]
}

我需要“file_id”值

我的代码如下

    Dim json As String = ModLinkData(n)
    Dim read = Newtonsoft.Json.Linq.JObject.Parse(json)
    Dim FileID As String = read.Item("files").ToString

这将正确地为我提供“文件”下的所有内容。我不知道如何获取 file_id 值。当我将“文件”更改为

Answer 1

我喜欢为此使用强类型，所以我会研究 JSON 序列化

您可以通过将 json 字符串复制到剪贴板在 .NET 中创建 class，然后

In Visual Studio put the cursor where you want the new classes
Edit >> Paste Special >> Paste JSON as Classes

结果是这样的（我已经在 Rootobject 中将一些数组类型更改为列表）

Public Class Rootobject
    Public Property files As List(Of File)
    Public Property file_updates As List(Of File_Updates)
End Class
Public Class File
    Public Property id As Integer()
    Public Property uid As Long
    Public Property file_id As Integer
    Public Property name As String
    Public Property version As String
    Public Property category_id As Integer
    Public Property category_name As String
    Public Property is_primary As Boolean
    Public Property size As Integer
    Public Property file_name As String
    Public Property uploaded_timestamp As Integer
    Public Property uploaded_time As Date
    Public Property mod_version As String
    Public Property external_virus_scan_url As String
    Public Property description As String
    Public Property size_kb As Integer
    Public Property size_in_bytes As Integer
    Public Property changelog_html As String
    Public Property content_preview_link As String
End Class
Public Class File_Updates
    Public Property old_file_id As Integer
    Public Property new_file_id As Integer
    Public Property old_file_name As String
    Public Property new_file_name As String
    Public Property uploaded_timestamp As Integer
    Public Property uploaded_time As Date
End Class

既然你已经引用了NewtonSoft.Json，我们可以使用其中的反序列化方法

Dim json = ModLinkData(n)

Dim rootobject = Newtonsoft.Json.JsonConvert.DeserializeObject(Of Rootobject)(json)

Dim fileIDs = rootobject.files.First().id ' this is an array
Dim fileID1 = fileIDs(0)
Dim fileID2 = fileIDs(1)

Console.WriteLine(fileID1)
Console.WriteLine(fileID2)

输出

6856
3667

如果您在设计时就知道数据的设计，那么这种方法优于您的方法，因为您获得了强类型化。比较

Dim FileID = read.Item("files")

到

Dim fileIDs = rootobject.files.First().id

并且在我的示例中看到 files 是对象的具体属性，而在您的示例中 files 是用于索引属性的可变字符串其中returns一个JToken

无论如何，我认为您遇到的主要问题是在返回数组时期望单个值，这在任何一种情况下都是一个问题，但是对于序列化，编译器会通知您而不是运行-时间。

Visual Basic 获取 Json 值

Visual Basic Get Json Value

vb.net

json