How do I assign a method that can be used by multiple properties

Question

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I would like to create a class/method that allows me to check if the value is within limits. I cannot figure out how to define the class/method for this. Here is some pseudo code:

VB

Class T
  Public a as integer
  Public b as integer
  Public c as integer

  Function check as Boolean
    return value>0 
  End Function
End Class

Use above like:

VB

dim myT as new T
  myT.a=9
  debug.writeline (myT.a.check)
  myT.b=-1
  debug.writeline (myT.b.check)
  myT.c=1
  debug.writeline (myT.c.check)

Display should be:
true
false
true

Please help me. Thank you

Posted 11-Nov-14 6:35am

Member 11183408

Updated 11-Nov-14 6:40am

DamithSL

v4

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bojammis · Accepted Answer · 2014-11-12T06:48:00

Hi there, here are two examples that may provide you an answer. The second Class T2 uses an extension method for type Integer as mentioned before this post. The first Class example uses a custom class to hold the integer value and supplies the functionality to check the value.

Imports System.Runtime.CompilerServices

Module Module1
    'This is my custom class to hold and check integer value
    Friend Class T
        Property A As New myInteger
        Property b As New myInteger
        Property c As New myInteger

        Friend Class myInteger
            Private _value As Integer
            Public Property Value() As Integer
                Get
                    Return _value
                End Get
                Set(ByVal value As Integer)
                    _value = value
                End Set
            End Property
            Friend Function Check() As Boolean
                Return CBool(Value > 0)
            End Function
        End Class
    End Class

    'This is your class from pseudo code.
    Friend Class T2
        Property A As Integer
        Property B As Integer
        Property C As Integer
    End Class

   'Run Code here
    Sub Main()

        Debug.WriteLine("Testing Class T")
        Dim myT As New T
        myT.A.Value = 9
        Debug.WriteLine(myT.A.Check)
        myT.b.Value = -1
        Debug.WriteLine(myT.b.Check)
        myT.c.Value = 1
        Debug.WriteLine(myT.c.Check)

        Debug.WriteLine("Testing Class T2")
        Dim myT2 As New T2
        myT2.A = 9
        Debug.WriteLine(myT2.A.ExtCheck)
        myT2.B = -1
        Debug.WriteLine(myT2.B.ExtCheck)
        myT2.C = 1
        Debug.WriteLine(myT2.C.ExtCheck)
    End Sub
    'Needed Extension method
    <Extension()>
    Public Function ExtCheck(ByVal value As Integer) As Boolean
        Return CBool(value > 0)
    End Function

End Module

I hope that helps.

Thomas Daniels · Accepted Answer · 2014-11-11T06:40:00

Solution 1

You don't need to have a function inside your class. You can have a function outside your class, like this:

VB.NET

Function Check(valueToCheck As Integer) As Boolean ' put this method outside your class
	Return valueToCheck > 0
End Function

Use the above method like this:

VB.NET

dim myT as new T
myT.a=9
debug.writeline (Check(myT.a))
myT.a=-1
debug.writeline (Check(myT.a))
myT.a=0
debug.writeline (Check(myT.a))

You can define the Check method in your class (and then you have to all it like myT.Check(myT.a)), but there is not really a reason for doing that (unless you really need it for a purpose, but there doesn't come one to my mind immediately).

Posted 11-Nov-14 6:40am

Thomas Daniels

Updated 11-Nov-14 7:17am

v5

Comments

Member 11183408 11-Nov-14 12:53pm

Thank you for your reply. I'm new to classes and was hoping to define the method in the class.

I know how to do it otherwise.

Thomas Daniels 11-Nov-14 13:14pm

You can define it in a class, and then you have to call it like myT.Check(myT.a), but there is not really a reason for doing that (unless you really need it for a purpose, but there doesn't come one to my mind immediately). I'll add that to my answer.

Member 11183408 11-Nov-14 13:22pm

Thank you. I just need to figure what benefit methods really have in classes.

Thomas Daniels 11-Nov-14 13:24pm

They have benefits if they access variables defined in the same class.

Member 11183408 11-Nov-14 13:51pm

For example. I would like to program a custom method (upper case) that would return the upper case string for any of the variables defined in my class. How would this work?

PS. I know that VB has upper case functions. This is just an example

Thomas Daniels 11-Nov-14 14:02pm

You could write it so it always works for one variable, like this:


Function SpecificVariableToUppercase() as String
    Return yourSpecificVariable.ToUpper()
End Function

You can use input to decide which variable, but that's not very easy and requires more code.

Member 11183408 11-Nov-14 14:30pm

Understood. My question focuses on Methods. How can I create a Method that applies to any property in an object?

Object.Property.Method

VB example Object.MyValue.toString returns a string of the value. Method (function) toString can be used for any property.

How can I define a function like toString?

Thomas Daniels 11-Nov-14 14:46pm

If you want to do that, you can use extension methods: http://msdn.microsoft.com/en-us/library/bb384936.aspx. Make sure to set the type of the parameter of the method to Object if you want that it applies to all objects.

Member 11183408 11-Nov-14 15:11pm

Thanks. Will investigate