VB: Problems with using variable from another class + what to do with not used interface`s functions - vb.net

Question

I have a problem with getting variable from another class and cannot understand what to do with interface`s functions which have already existed in another class.
What I have:
Form where clicking on a button I should see reversed string:
(I want to call pooraja.StringReverse which is below)
Private Sub btnPoora1_Click(sender As System.Object, e As System.EventArgs) _
Handles btnPoora1.Click
'Dim text As PrjTekstiPooraja.ITeisendused = New PrjTekstiPooraja.CtekstiPooraja
Dim text As PrjTekstiPooraja.ITeisendused = New PrjTekstiPooraja.CtekstiPooraja
Dim pooraja As PrjTekstiPooraja.ITeisendused = New PrjTekstiPooraja.CAlgrotimilinePooraja
text.strText = txtSisendTekst.Text
txtValjundTekst1.Text = pooraja.stringReverse
text.intStart = 1
text.intEnd = Len(txtSisendTekst.Text)
ascFSymbol.Text = text.ascFirstSymbol
ascLSymbol.Text = text.ascLastSymbol()
End Sub
CtekstiPooraja:
(Thiss class will be used to store data.Under data I mean strPooratavText. Data will be used in CAlgoritmilinePooraja)
Public Class CtekstiPooraja
Implements ITeisendused
Public intStartSymbol As Integer
Public intEndSymbol As Integer
Public strPooratavText As String
Private Property intEnd As Integer Implements ITeisendused.intEnd
Get
Return intEndSymbol
End Get
Set(ByVal value As Integer)
intEndSymbol = value
End Set
End Property
Private Property intStart As Integer Implements ITeisendused.intStart
Get
Return intStartSymbol
End Get
Set(ByVal value As Integer)
intStartSymbol = value
End Set
End Property
Public Function pooraText() As String Implements ITeisendused.pooraText
Return StrReverse(strPooratavText)
End Function
Public Property strText As String Implements ITeisendused.strText
Get
Return strPooratavText
End Get
Set(ByVal value As String)
strPooratavText = value
MsgBox(strPooratavText)
End Set
End Property
Public Sub teisendaText(ByRef strSisendText As String) Implements ITeisendused.teisendaText
strPooratavText = StrReverse(strSisendText)
End Sub
Public Function ascFirstSymbol() As String Implements ITeisendused.ascFirstSymbol
Return Asc(GetChar(strPooratavText, intStartSymbol))
End Function
Public Function ascLastSymbol() As String Implements ITeisendused.ascLastSymbol
Return Asc(GetChar(strPooratavText, intEndSymbol))
End Function
Public Function stringReverse() As String Implements ITeisendused.stringReverse
Return Nothing
End Function
End Class
CAlgrotimilinePooraja:
(This class will be called by form button. There I need to use stringReverse function with data from CtekstiPooraja. The problem is that everywhere is used the same interface and there is some functions and procedures from this interface which isnt necessary. I dont know what value should return these unused functions/procedures. Just using "return Nothing or return 0/ "" is bad idea, may be there is possible somehow referenceto to CTekstiPooraja functions/procedures variables")
Public Class CAlgrotimilinePooraja
Implements ITeisendused
Private x As New PrjTekstiPooraja.CtekstiPooraja
Public Function stringReverse() As String Implements ITeisendused.stringReverse
MsgBox(x.strPooratavText)
Dim i As Integer = 0
Dim j As Integer
Dim characters(j) As Char
Dim newString(j) As Char
characters = x.strPooratavText.ToCharArray()
newString = x.strPooratavText.ToCharArray()
Do While i <= j - 1
newString(i) = characters(j - 1)
newString(j - 1) = characters(i)
i += 1
j -= 1
Loop
Return newString
End Function
Public Function ascFirstSymbol() As String Implements ITeisendused.ascFirstSymbol
Return x.ascFirstSymbol()
End Function
Public Function ascLastSymbol() As String Implements ITeisendused.ascLastSymbol
Return Nothing
End Function
Public Property intEnd As Integer Implements ITeisendused.intEnd
Get
Return x.intEndSymbol
End Get
Set(ByVal value As Integer)
End Set
End Property
Public Property intStart As Integer Implements ITeisendused.intStart
Get
Return x.intStartSymbol
End Get
Set(ByVal value As Integer)
End Set
End Property
Public Function pooraText() As String Implements ITeisendused.pooraText
Return x.pooraText()
End Function
Public Property strText As String Implements ITeisendused.strText
Get
Return x.strPooratavText
End Get
Set(ByVal value As String)
End Set
End Property
Public Sub teisendaText(ByRef strSisendText As String) Implements ITeisendused.teisendaText
x.strPooratavText = StrReverse(strSisendText)
End Sub
End Class
MyInterface:
Public Interface ITeisendused
Property intStart As Integer
Property intEnd As Integer
Property strText As String
Function pooraText() As String
Function ascFirstSymbol() As String
Function ascLastSymbol() As String
Function stringReverse() As String
Sub teisendaText(ByRef strSisendText As String)
End Interface
I cannot understand how to get variable strPooratavText from CTekstiPooraja to CAlgrotimilinePooraja. Usually that instancewhich I create worked but not now. And I cannot understand what to do with already existed function and procedures in CAlgoritmilinePooraja when the same function and procedures has in another class. Maybe, it is possible to reference them somehow to existed functions/procedures in CTekstiPooraja? Could you explain me how to id, already tired to surf Internet to find a solution for it, have already try a lot.

Answer 1

Well, I think you have a fundamental problem with understanding interfaces. They describe data and behavior, it should be extremely rare to want to implement part of an interface.
That said, if you do want to implement part of an interface, instead of returning bogus data, throw an exception for behavior you don't implement.
Your specific problem is that CAlgoritmilinePooraja works on an instance of CtekstiPooraja, but it creates a new instance instead of using an existing one. Add
Sub New(incomingX as CtekstiPooraja)
x = incomingX
End Sub
to CAlgoritmilinePooraja. And then in your event, use....
Dim text As PrjTekstiPooraja.CtekstiPooraja = New PrjTekstiPooraja.CtekstiPooraja
text.strText = txtSisendTekst.Text
Dim pooraja As PrjTekstiPooraja.ITeisendused = New PrjTekstiPooraja.CAlgrotimilinePooraja(text)
That is the minimum change to your design that gets what you want to happen to happen but it's problably not what you should do. Other than implementing strReverse, CtekstiPooraja seems to be what you want, CAlgrotimilinePooraja looks to do just one thing, the actual string reversal.
I would move the implementation of strReverse into CtekstiPooraja, and then eliminate CAlgrotimilinePooraja.
PS I would try to stick to English for class names as well as functions and variables.