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    « Kotlin the data class and the classAnother thing you should never do in VB.Net »
    0
    comments

    Json.Net 's JObject to dynamic in VB.Net

    by Christiaan Baes (chrissie1) on Nov 11, 2012 in categories Microsoft Technologies, VB.NET
    Instapaper

    In my previous post I showed you how to get an object from a call to a SignalR method.

    That call on the client side returns a Json.Net JObject. This is dynamic object.

    However, the implementation of this object is not very VB.Net friendly.

    If you try this.

    vbnet
    Line number Off | Hide | Select all
    1. Imports System.Runtime.CompilerServices
    2. Imports Newtonsoft.Json
    3. Imports Newtonsoft.Json.Linq
    4. Imports Microsoft.AspNet.SignalR.Client.Hubs
    5.  
    6. Module Module1
    7.  
    8.     Sub Main()
    9.         Dim connection = New HubConnection("http://localhost:50865")
    10.  
    11.         Dim plants = connection.CreateHubProxy("Plants")
    12.  
    13.         plants.On(Of String)("addMessage", Sub(data) Console.WriteLine(data.ToString()))
    14.  
    15.         connection.Start().Wait()
    16.  
    17.         Dim line As String = Nothing
    18.         Console.WriteLine("type the id + enter to send, type exit + enter to exit.")
    19.         While line <> "exit"
    20.             line = Console.ReadLine()
    21.             plants.Invoke(Of Object)("GetPlant", line).ContinueWith(Sub(data)
    22.                                                                         If data.Result IsNot Nothing Then
    23.                                                                             Console.WriteLine(data.Result.ToString)
    24.                                                                             Dim result = data.Result
    25.                                                                             Console.WriteLine(result.Id)
    26.                                                                             Console.WriteLine(result.Genus)
    27.                                                                             Console.WriteLine(result.Species)
    28.                                                                             For Each commonName In result.CommonNames
    29.                                                                                 Console.WriteLine(commonName)
    30.                                                                             Next
    31.                                                                         Else
    32.                                                                             Console.WriteLine("No plant with that id.")
    33.                                                                         End If
    34.                                                                     End Sub)
    35.         End While
    36.     End Sub
    37.  
    38. End Module

    You will get an exception on result.Id

    System.MissingMemberException was unhandled by user code
    HResult=-2146233070
    Message=Public member 'Id' on type 'JObject' not found.
    Source=Microsoft.VisualBasic
    StackTrace:
    at Microsoft.VisualBasic.CompilerServices.Symbols.Container.GetMembers(String& MemberName, Boolean ReportErrors)
    at Microsoft.VisualBasic.CompilerServices.NewLateBinding.ObjectLateGet(Object Instance, Type Type, String MemberName, Object[] Arguments, String[] ArgumentNames, Type[] TypeArguments, Boolean[] CopyBack)
    at Microsoft.VisualBasic.CompilerServices.NewLateBinding.FallbackGet(Object Instance, String MemberName, Object[] Arguments, String[] ArgumentNames)
    at CallSite.Target(Closure , CallSite , Object )
    at System.Dynamic.UpdateDelegates.UpdateAndExecute1[T0,TRet](CallSite site, T0 arg0)
    at Invoker(CallSiteBinder , Object , Object[] )
    at Microsoft.VisualBasic.CompilerServices.IDOUtils.CreateRefCallSiteAndInvoke(CallSiteBinder Action, Object Instance, Object[] Arguments)
    at Microsoft.VisualBasic.CompilerServices.IDOBinder.IDOGet(IDynamicMetaObjectProvider Instance, String MemberName, Object[] Arguments, String[] ArgumentNames, Boolean[] CopyBack)
    at Microsoft.VisualBasic.CompilerServices.NewLateBinding.LateGet(Object Instance, Type Type, String MemberName, Object[] Arguments, String[] ArgumentNames, Type[] TypeArguments, Boolean[] CopyBack)
    at SignalRConsole.Module1._Lambda$__2(Task`1 data) in E:\Users\christiaan\Documents\Visual Studio 2012\Projects\SignalRTesting\SignalRConsole\Module1.vb:line 25
    at System.Threading.Tasks.ContinuationTaskFromResultTask`1.InnerInvoke()
    at System.Threading.Tasks.Task.Execute()
    InnerException:

    The problem is the LateGet. But you can found out all about why this is a problem for VB.Net in the following post by Matthew Doig.

    And none of the Json.net converters can solve this for us.

    But we can use another library that does work with VB.Net.

    And it's called JSonFX. Just add it to your project via Nuget and then we can change our code to this.

    vbnet
    Line number Off | Hide | Select all
    1. Imports System.Runtime.CompilerServices
    2. Imports Newtonsoft.Json
    3. Imports Newtonsoft.Json.Linq
    4. Imports Microsoft.AspNet.SignalR.Client.Hubs
    5.  
    6. Module Module1
    7.  
    8.     Sub Main()
    9.         Dim connection = New HubConnection("http://localhost:50865")
    10.  
    11.         Dim plants = connection.CreateHubProxy("Plants")
    12.  
    13.         plants.On(Of String)("addMessage", Sub(data) Console.WriteLine(data.ToString()))
    14.  
    15.         connection.Start().Wait()
    16.  
    17.         Dim line As String = Nothing
    18.         Console.WriteLine("type the id + enter to send, type exit + enter to exit.")
    19.         While line <> "exit"
    20.             line = Console.ReadLine()
    21.             plants.Invoke(Of Object)("GetPlant", line).ContinueWith(Sub(data)
    22.                                                                         If data.Result IsNot Nothing Then
    23.                                                                             Console.WriteLine(data.Result.ToString)
    24.                                                                             Dim reader = New JsonFx.Json.JsonReader()
    25.                                                                             Dim result = reader.Read(data.Result.ToString)
    26.                                                                             Console.WriteLine(result.Id)
    27.                                                                             Console.WriteLine(result.Genus)
    28.                                                                             Console.WriteLine(result.Species)
    29.                                                                             For Each commonName In result.CommonNames
    30.                                                                                 Console.WriteLine(commonName)
    31.                                                                             Next
    32.                                                                         Else
    33.                                                                             Console.WriteLine("No plant with that id.")
    34.                                                                         End If
    35.                                                                     End Sub)
    36.         End While
    37.     End Sub
    38.  
    39. End Module

    Now our result will be.

    type the id + enter to send, type exit + enter to exit.
    1
    {
    "Id": 1,
    "Genus": "Fagus",
    "Species": "Sylvatica",
    "CommonNames": [
    "Common Beech"
    ]
    }
    Someone requested id: 1
    1
    Fagus
    Sylvatica
    Common Beech

    Which is ultra cool.

    About the Author

    User bio imageChris is awesome.
    Social SitingsTwitterHomePageLTD RSS Feed
    1996 views
    Read More Posts by Christiaan Baes (chrissie1)
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