如何从嵌套在 json 数组中的对象访问数据

Question

我需要访问嵌套的 json 对象数组中的数据以便能够进一步操作它，使用 vb.net 4.0 中的 javascriptserializer。

示例字符串如下：

json: {"multicast_id":216,"success":3,"failure":3,"canonical_ids":1,"results":[{"message_id":"1:0408"},{"errord":"Unavailable"}]}

这是我到目前为止编写的代码：

Class main
Public Property multicast_id As Integer
Public Property success As Integer
Public Property failure As Integer
Public Property canonical_ids As Integer
Public Property results As Results()
End Class

Class Results
Public Property message_id As String
Public Property errord As String
End Class


Public Class Form1

Private Sub btnTest_Click(sender As Object, e As EventArgs) Handles btnTest.Click
    Dim json As String
    json = txtInsert.Text

    Try
        Dim ser As JavaScriptSerializer = New JavaScriptSerializer()
        Dim exmp As main = New main
        exmp = ser.Deserialize(Of main)(json)

        Console.WriteLine(exmp.canonical_ids)
        Console.WriteLine(exmp.multicast_id)

        For Each item As Object In exmp.results
            For Each example As String In item
                Console.WriteLine("example")
            Next
        Next

    Catch ex As Exception
        MsgBox(ex.ToString)
    End Try
End Sub
End Class

我在每个语句的内部都遇到了错误。如果有人能帮我解决这个问题，我将不胜感激。

Answer 1

您不需要内部的 For Each。您已经在第一个循环中旋转数组。您也可以更具体地指定循环中的类型：

    For Each item As Results In exmp.results
        Console.WriteLine(item.message_id & " : " & item.errord)
    Next

Answer 2

您正在正确获取嵌套对象。

相反，您的问题是，一旦您获得该嵌套对象，您就会尝试使用 For Each 来获取该结果的每个字符串属性。那是无效的。

例如，这不起作用，因为 Results 没有实现 IEnumerable，所以您不能在 in:

上使用 For Each

Dim r as new Results();
r.message_id = "1:0408"
r.errord = "Unavailable"
For Each example As String In r ' <- this will throw an error
Next

一旦您获得了对 Results 的引用，您就需要通过属性名称访问它：

For Each item As Results In exmp.results
    Console.WriteLine("message_id: {0}", item.message_id)
    Console.WriteLine("errord: {0}", item.errord)
Next

如果您需要按名称访问属性，请将结果更改为不同的类型。

例如，您可以将结果定义为 Dictionary(of String, Object) 的数组，如下所示：

Class main
    Public Property multicast_id As Integer
    Public Property success As Integer
    Public Property failure As Integer
    Public Property canonical_ids As Integer
    Public Property results As Dictionary(Of String, Object)()
End Class

那么你可以使用：

For Each item As Object In exmp.results 'item will be a Dictionary(Of String, Object)
    For Each example As Object In item ' example will be a KeyValuePari(Of String, Object)
        Console.WriteLine(example.key)
        Console.WriteLine(example.value)
    Next
Next

或这样的名字：

    For Each item As Object In exmp.results 'item will be a Dictionary(Of String, Object)
        Console.WriteLine(item("message_id"))
        Console.WriteLine(item("errord"))
    Next
Next

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