How to make Arrays of Object in VB.net? - vb.net

Question

I am unable to debug this.
Is my procedure of array-making wrong?
The error it shows is
System.NullReferenceException :'Object reference not set to an instance of an object'
Module Module1
Class Toy
Private Name, ID As String
Private Price As Single
Private MinimumAge As Integer
Dim Count As Integer
Public Sub New()
End Sub
Public Sub SetName(ByVal N As String)
Name = N
End Sub
Public Sub SetID(ByVal I As String)
'VALIDATION CHECK FOR ID !
While Len(I) < 4
Console.WriteLine("Kindly Enter the ID with Lenght of Max 4 Characters")
End While
ID = I
End Sub
Public Sub SetPrice(ByVal SP As Single)
Price = SP
End Sub
Public Sub SetUserAge(ByVal SM As Integer)
'VALIDATION CHECK FOR AGE
While SM < 0 Or SM < 18
Console.WriteLine("Minimum age is 18")
End While
MinimumAge = SM
End Sub
Public Function GetName()
Return Name(Count)
End Function
Public Function GetID()
Return ID
End Function
Public Function GetPrice()
Return Price
End Function
Public Function GetAge()
Return MinimumAge
End Function
End Class
Class ComputerGame
Inherits Toy
Private Category, Consol As String
Public Sub New()
End Sub
Public Sub SetConsole(ByVal C As String)
While C <> "PS4" Or C <> "XBOX"
Console.WriteLine("Invalid console entered")
End While
Consol = C
End Sub
Public Sub SetCategory(ByVal SC As String)
Category = SC
End Sub
Public Function GetConsole()
Return Consol
End Function
Public Function GetCategory()
Return Category
End Function
End Class
Class Vehicle
Inherits Toy
Private Type As String
Private Length, Height, Weight As Single
Public Sub New()
End Sub
Public Sub SetType(ByVal TY As String)
While TY <> "Car" Or TY <> "Bus" Or TY <> "Truck"
Console.WriteLine("vehicle is not in list !")
End While
Type = TY
End Sub
Public Sub SetLength(ByVal SL As Single)
Length = SL
End Sub
Public Sub SetHeight(ByVal SH As Single)
Height = SH
End Sub
Public Sub SetWeight(ByVal SW As Integer)
Weight = SW
End Sub
Public Function GetT()
Return Type
End Function
Public Function GetLength()
Return Length
End Function
Public Function GetHeight()
Return Height
End Function
Public Function GetWeight()
Return Weight
End Function
End Class
Sub Main()
Dim ThisGame(6) As Toy
ThisGame(6) = New Toy
ThisGame(1).SetID("23456a")
ThisGame(2).SetID("236789b")
Console.WriteLine(ThisGame(1).GetID)
Console.ReadKey()
End Sub
End Module

Answer 1

This is what your Toy class should look like using the long method of Properties. Notice that you have Public Properties and a private field to store the values (sometimes called a backer field) Each Property has a Get and a Set procedure where you can add your validation code.
Public Class Toy
Private _Name As String
Public Property Name As String
Get
Return _Name
End Get
Set(value As String)
_Name = value
End Set
End Property
Private _ID As String
Public Property ID As String
Get
Return _ID
End Get
Set(value As String)
If value.Length < 4 Then
Console.WriteLine("Kindly Enter the ID with Lenght of Max 4 Characters")
Exit Property
End If
_ID = value
End Set
End Property
Private _Price As Single
Public Property Price As Single
Get
Return _Price
End Get
Set(value As Single)
_Price = value
End Set
End Property
Private _MinimumAge As Integer
Public Property MinimumAge As Integer
Get
Return _MinimumAge
End Get
Set(value As Integer)
If value < 0 Or value < 18 Then
Console.WriteLine("Minimum age is 18")
Exit Property
End If
_MinimumAge = value
End Set
End Property
Private _Count As Integer
Public Property Count As Integer
Get
Return _Count
End Get
Set(value As Integer)
_Count = value
End Set
End Property
End Class
Current versions have Automatic Properties where the compiler provides the getter, setter, and backer fields. Notice that you can still write your own Get and Set where you need to add code.
Public Class Toy
Public Property Name As String
Public Property Price As Single
Public Property Count As Integer
Private _ID As String
Public Property ID As String
Get
Return _ID
End Get
Set(value As String)
If value.Length < 4 Then
Console.WriteLine("Kindly Enter the ID with Lenght of Max 4 Characters")
Exit Property
End If
_ID = value
End Set
End Property
Private _MinimumAge As Integer
Public Property MinimumAge As Integer
Get
Return _MinimumAge
End Get
Set(value As Integer)
If value < 0 Or value < 18 Then
Console.WriteLine("Minimum age is 18")
Exit Property
End If
_MinimumAge = value
End Set
End Property
End Class
Please read the in line comments in regards to your array.
Sub Main()
Dim ThisGame(6) As Toy 'You are defining and array with 7 elements of Toy
'Each element is Nothing at this point and you will get a null exception error if you
'try to access an element.
ThisGame(6) = New Toy 'Here you have created an instance of your class for the 7th element
'The other six elements are still nothing so the next 3 lines will get
'NullReferenceException: 'Object reference not set to an instance of an object.'
'ThisGame(1).ID = "23456a"
'ThisGame(2).ID = "236789b"
ThisGame(1) = New Toy
ThisGame(1).ID = "23456a"
ThisGame(2) = New Toy
ThisGame(2).ID = "236789b"
'Remember the first element in you array is ThisGame(0)
Console.WriteLine(ThisGame(1).ID)
Console.ReadKey()
End Sub