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Facilitating JSON, LINQ, and VB.NET

Friday Dec 15th 2017 by Hannes DuPreez

Discover how to read JSON data using LINQ in Visual Basic to make your coding less of a headache.

Introduction

JSON is a strange creature that you learn to love over time; LINQ, if you do not understand it, is the same. Today, I'd like to make your JSON and LINQ headaches disappear by showing you how to read JSON data using LINQ in Visual Basic.

LINQ

Language-Integrated Query (LINQ) adds query capabilities to Visual Basic. LINQ uses a unified syntax irrespective of the type of data. Instead of sending a query to a database, or working with different query syntax for different types of data that are being searched, LINQ provides queries as part of the Visual Basic language.

Practical

Open Visual Studio and create a new Visual Basic Windows Forms project. Design your form to resemble Figure 1. Keep in mind, as always, my object names may be different than yours.

Design
Figure 1: Design

Add the following Namespaces to make it part of your Class:

Imports System.IO
Imports System.Net
Imports Newtonsoft.Json
Imports Newtonsoft.Json.Linq

You may notice the bottom two Imports. These include external libraries from Newtonsoft. You can download these libraries from the link provided. After you have downloaded the Newtonsoft libraries(s), you need to set a reference to the .dll files. You do this by clicking Project, Add reference, Browse, and locating your .dll file.

Create a Modular variable that will hold your JSON string and populate it:

   Private strIcons As String = "[
      {
         'Name': 'Chester',
         'Surname': 'Bennington',
         'Age': '41',
         'Gender': 'm'
      },
      {
         'Name': 'Kurt',
         'Surname': 'Cobain',
         'Age': '27',
         'Gender': 'm'
      },
      {
         'Name': 'Kirk',
         'Surname': 'Hammet',
         'Age': '55',
         'Gender': 'm'
      },
      {
         'Name': 'Bruce',
         'Surname': 'Dickensen',
         'Age': '59',
         'Gender': 'm'
      },
      {
         'Name': 'Dave',
         'Surname': 'Mustaine',
         'Age': '56',
         'Gender': 'm'
      },
      {
         'Name': 'Freddie',
         'Surname': 'Mercury',
         'Age': '45',
         'Gender': 'm'
      },
      {
         'Name': 'Axl',
         'Surname': 'Rose',
         'Age': '55',
         'Gender': 'm'
      },
      {
         'Name': 'Prince',
         'Surname': '-',
         'Age': '57',
         'Gender': 'm'
      }
   ]"

Even for the untrained eye, it should be quite apparent that there are eight objects inside this string. Each of these objects contain sub-items for name, Surname, Age and Gender. Each of these sub-items has its own content. Do not judge my taste in music… :)

Here is more information about JSON.

The trick now is to read this content and separate it logically. This is where LINQ is extremely powerful. Add the following code:

   Private Sub Button1_Click(sender As Object, e As EventArgs) _
         Handles Button1.Click

      Try

         GetIcons(strIcons)

      Catch ex As WebException

         MessageBox.Show("Error: " & ex.ToString())

      End Try

   End Sub

   Private Sub GetIcons(strJSON As String)

      Dim Icons = JsonConvert.DeserializeObject(Of List(Of _
         clsIcons))(strJSON)

      For Each Legend In Icons

         ListBox1.Items.Add(Legend.Name)
      Next



   End Sub
   Public Class clsIcons

      Public Name As String
      Public Surname As String
      Public Age As String
      Public Gender As String

   End Class

The geticons sub-procedure deserializes a JSON string and stores each segment neatly in a class named strIcons. When you run your project and click the first button, your list will be displayed inside the leftmost listbox (see Figure 2).

Name segments from the supplied JSON string
Figure 2: Name segments from the supplied JSON string

Add the following code behind the second button:

   Private Sub Button2_Click(sender As Object, e As EventArgs) _
         Handles Button2.Click

      Dim Icons = JsonConvert.DeserializeObject(Of List(Of _
         clsIcons))(strIcons)

      Dim lstIcons = From Legend In Icons Where _
         Legend.Name.Contains("Kurt") Select Legend

      For Each Legend In lstIcons

         ListBox2.Items.Add("Icon: " & Legend.Name & " " _
            & Legend.Surname & " Age: " + Legend.Age)

      Next

   End Sub

The preceding code manipulates the JSON object a bit further and enables you to loop through each of the items inside the JSON list with the help of LINQ. Figure 3 shows this code in action.

JSON read with the help of LINQ
Figure 3: JSON read with the help of LINQ

Usually, a JSON string gets supplied in the form of a file. Let's add that code now:

   Dim srIcons As StreamReader

      Try
         Dim strURL As String = "http://website.com/ _
            calltoJSONfunction?iconlist=legends&format=json"

         Dim wrIcons As HttpWebRequest = _
            CType(WebRequest.Create(strURL), HttpWebRequest)
         Dim wrReponse As HttpWebResponse = _
            CType(wrIcons.GetResponse(), HttpWebResponse)

         srIcons = New StreamReader(wrReponse.GetResponseStream())

         Dim strInput As String = srIcons.ReadToEnd()

         GetIcons(strIcons)

      Catch ex As WebException

         MessageBox.Show("Error: " & ex.ToString())

      End Try

   End Sub

Here, you make use of the System.Net functionalities to read the JSON file from the supplied URL. Figure 4 shows this code in action:

JSON read from a file
Figure 4: JSON read from a file

The code for this article is available on GitHub.

Conclusion

JSON is not too complicated to understand; neither is LINQ. This is just the tip of the iceberg, though. The onus is now on you to take what you have learned today further.

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