Reference to a non-shared member...

So in my class we have an assignment to create a cash register. I got it to work fine originally but the assignment calls for a class called CashRegister(which I have never done before), a property called Balance, and add method and a subtract method. So I tried to do that but now all my text boxes, when I reference them, are giving me the error "reference to a nonshared member..". HOw do i fix this? My code is:

Code:

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Public Class frmRegister
    Private Sub frmRegister_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If txtBalance.Text = "" Then
            txtBalance.Text = "0"
        End If
    End Sub
    Class CashRegister
        Private Balance As Integer
        Private addAmount As Double
        Private subAmount As Double
        Public Property AddMethod As Double
            Get
                Return addAmount
            End Get
            Set(ByVal value As Double)
                Dim x As Integer = Val(txtAmount.Text)
                Dim y As Integer = Val(txtBalance.Text)
                addAmount = x + y
            End Set
        End Property
        Public Property SubtractMethod As Double
            Get
                Return subAmount
            End Get
            Set(ByVal value As Double)
                Dim x As Integer = Val(txtAmount.Text)
                Dim y As Integer = Val(txtBalance.Text)
                subAmount = y - x
            End Set
        End Property

        Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
            txtBalance.Text = FormatCurrency(addAmount)
        End Sub

        Private Sub btnSubtract_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSubtract.Click
         
            txtBalance.Text = FormatCurrency(subAmount)
            If txtBalance.Text < 0 Then
                MessageBox.Show("Transaction Cannot Result in Negative Balance!")
                txtBalance.Text = "0"
            End If

        End Sub

    End Class
End Class

---

ANy help would be appreciated?

there's a few thing wrong there... first your class is inside the form... that just makes it only visible inside the class.
next, your class references items on the form... it should NEVER do that.
Lastly, you've got some event handlers inside the class... again... that's not what you want... they shouldbe outside the class in the form.

-tg

So then how do i get the values from the text boxes if I can't reference them? could you please provide examples of what you mean as I don't totally understand what you're telling me. should the form be inside the class then or two separate entities?

Code:

---

Class CashRegister
    Private Balance As Integer
    Private addAmount As Double
    Private subAmount As Double
    Public Property AddMethod As Double
        Get
            Return addAmount
        End Get
        Set(ByVal value As Double)
            Dim x As Integer = value
            Dim y As Integer = value
            addAmount = x + y
        End Set
    End Property
    Public Property SubtractMethod As Double
        Get
            Return subAmount
        End Get
        Set(ByVal value As Double)
            Dim x As Integer = value
            Dim y As Integer = value
            subAmount = y - x
        End Set
    End Property
End Class
Public Class frmRegister
    Private Sub frmRegister_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
        If txtBalance.Text = "" Then
            txtBalance.Text = "0"
        End If
    End Sub
    Private Sub btnAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnAdd.Click
        txtBalance.Text = FormatCurrency(AddMethod)
    End Sub

    Private Sub btnSubtract_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnSubtract.Click

        txtBalance.Text = FormatCurrency(SubMethod)
        If txtBalance.Text < 0 Then
            MessageBox.Show("Transaction Cannot Result in Negative Balance!")
            txtBalance.Text = "0"
        End If

    End Sub

End Class

---

So this is closer to the original example I had and I think its closer to what you're saying I should do, but I have no idea. I don't understand how I can do the equations without using the textboxes. So when I try to call back the methods with the equations, how do they know which value gets assigned to which. Also, with the code like this, the methods aren't recognized and I know something is definitely wrong with the way its set up. Could someone please help? Remember, I am a newbie and just recently watched a video on classes. I can easily make this register work without a class but for my assignment I need to class it.

Quote:

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So then how do i get the values from the text boxes if I can't reference them?

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How does any class (form, textbox, label, whatever) get its values? That's what it has properties for. You assign values to the properties of an instance of the class from whatever source is appropriate. You don't define (and therefore constrain) that source within the property.

Quote:

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should the form be inside the class then or two separate entities?

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If you really need to ask this (or at least the first part of it) then I suggest you need to go back and start again. It is, as TG clearly states, possible to define a class within the form class BUT in that case it will not be accessible from anywhere other than within the form should you later add further forms or modules to the program. The normal practice is therefore to add new classes as Public objects outside the form structure.

Could you please show me some examples, it doesn't even have to relate to my code. I just don't understand. In the videos they referenced the textboxes and they worked but I can't seem to do that at all

vb.net Code:

Class CashRegister
    Private Balance As Integer
    Private addAmount As Double
    Private subAmount As Double
    Public Property AddMethod As Double ' how could AddMethod possibly be a property? A function perhaps?
        Get
            Return addAmount
        End Get
        Set(ByVal value As Double) ' so if I had an instance of CashRegister called CR1 and assigned the value
                                                 ' CR1.AddMethod = 7, CR1.AddMethod would = 14 ???????????????
            Dim x As Integer = value
            Dim y As Integer = value
            addAmount = x + y
        End Set
    End Property
    Public Property SubtractMethod As Double
        Get
            Return subAmount
        End Get
        Set(ByVal value As Double)
            Dim x As Integer = value
            Dim y As Integer = value
            subAmount = y - x          ' and CR1.SubtractMethod = 0 ???????
        End Set
    End Property
End Class

The class has some issues. For one thing, those shouldn't be properties, they should be functions. You want to take two arguments and return a single value. A property is used to set a member variable, or return a member variable in a class instance. What you should have for AddMethod is this:

Code:

---

Public Function AddMethod(firstValue as double, secondValue as double) As Double
 return firstValue + secondValue
End Function

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Except that that isn't right, either. I see you have Balance as a class member. That should be exposed as a ReadOnly property (no Set method at all). That also makes the AddMethod a bit different depending on what it is supposed to do. The function I wrote does what your property was doing, but that doesn't seem right, because what is the purpose of a balance member in a class called CashRetgister if the AddMethod function does nothing but add two numbers together and return the result? It seems more likely that what you want is something like this:

Code:

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Public ReadOnly Property TheBalance As Double
 Get
  Return Balance
 End Get
End Property

Public Sub AddMethod(newValue as Double)
 Balance += newValue
End Sub

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The form would still need to have an instance of the CashRegister class as a member for you to use it. You'd then properly convert the strings from the Textbox and pass them as the argument to the AddMethod.

Two posts while I was writing that, but what I wrote was kind of similar to what dunfiddlin was getting at.