ReadOnly properties in Vb.Net

Sougata Ghosh 161 Reputation points
2021-04-22T15:46:15.747+00:00

Hi,

What is the difference between a property declared as ReadOnly and a property that has a public Get method but a private SET method? Are these two things not equivalent? If they are, then why do we have two ways of doing the same thing?

Regards,
Sougata Ghosh

VB
VB
An object-oriented programming language developed by Microsoft that is implemented on the .NET Framework. Previously known as Visual Basic .NET.
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  1. Duane Arnold 3,211 Reputation points
    2021-04-22T16:21:11.653+00:00

    They both achieve the same thing. You cannot set data in the property. I'll assume it does it internally with the Read-only attribute as opposed to making the Set Private or one doesn't have the Set in the property. Either way you want to do it, it's a read-only property.

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  1. Peter Fleischer (Freelancer) 17,571 Reputation points
    2021-04-23T17:19:14.21+00:00

    Hi,
    there are differences.

    A value for the read-only property that you can set only once during instantiation (constructor or direct assignment to the property).

    A value of the property with a private setter that you can set at any time during execution, but only within the class (object).

    Try following console demo:

    Module Module75
      Sub Main()
        Try
          Dim c As New Demo
          c.Execute()
        Catch ex As Exception
          Console.WriteLine(ex.ToString)
        End Try
        Console.WriteLine("Continue enter key")
        Console.ReadKey()
      End Sub
      Friend Class Demo
        Friend Sub Execute()
          Try
            Dim c As New DemoProp("Prop 1")
            c.SetPropValue("Prop 3")
            Console.WriteLine(c.ROProp1)
            Console.WriteLine(c.ROProp2)
            Console.WriteLine(c.PrivateSetterProp)
          Catch ex As Exception
            Console.WriteLine(ex.Message)
          End Try
        End Sub
      End Class
    
      ''' <summary>
      ''' Demo class with different properties
      ''' </summary>
      Public Class DemoProp
    
        ''' <summary>
        ''' Constructor
        ''' </summary>
        ''' <param name="parameter">value to initial set readonly property</param>
        Public Sub New(parameter As String)
          ROProp1 = parameter
        End Sub
    
        ''' <summary>
        ''' readonly property with value from constructor
        ''' </summary>
        ''' <returns>value assigned in constructor</returns>
        Public ReadOnly Property ROProp1 As String
    
        ''' <summary>
        ''' readonly property with assigned value 
        ''' </summary>
        ''' <returns>assigned value during instantiation</returns>
        Public ReadOnly Property ROProp2 As String = "Prop 2"
    
        ''' <summary>
        ''' backing field
        ''' </summary>
        Private _privatesetterProp As String
        ''' <summary>
        ''' property with private setter
        ''' </summary>
        ''' <returns>backing field</returns>
        Public Property PrivateSetterProp As String
          Get
            Return Me._privatesetterProp
          End Get
          Private Set(value As String)
            Me._privatesetterProp = value
          End Set
        End Property
    
        ''' <summary>
        ''' method to use property with private setter
        ''' </summary>
        ''' <param name="parameter">value to use private setter</param>
        Public Sub SetPropValue(parameter As String)
          PrivateSetterProp = parameter
        End Sub
    
      End Class
    
    End Module