Can I write Copy Constructor in VB?

[benfly08]

Hi, guys.
I'm debugging a VB program that is written by the guy who already left the company. I found out the main problem is that the guy used object assignment which will mess up the data. For example, I have a customized class as following:

Public Class testCell
    Private _name As String = ""
    Private isCopied As Boolean = False
 
    Public Property Name() As String
        Get
            Return _name
        End Get
        Set(ByVal Value As String)
            _name = Value
        End Set
    End Property
 
    Public Property isCopy() As Boolean
        Get
            Return isCopied
        End Get
        Set(ByVal Value As Boolean)
            isCopied = Value
        End Set
    End Property
 
    Public Sub Reset()
        _name = ""
        isCopied = False
    End Sub
End Class
 

And in my main program, I have:

        Dim cell1 As testCell = New testCell
        Dim cell2 As testCell = New testCell
 
        cell1 = cell2
 
        cell2.Name = "Ben"
        If cell1.Name = "Ben" Then
            MsgBox("Object is referenced")
        End If
 

Run the main program, I will get the message box pop up. But this is not what I want. All I want is to copy property values in cell2 to cell1, instead of reference cell2 to cell1.

Now I know I can use:

cell1.Name = cell2.Name
cell1.isCopy = cell2.isCopy
 

to achieve what i really want. But in real life, if the class has hundreds of properties, this is not the right way to do it. So I want to create a copy constructor as I can do in C++, anybody knows how to do it in VB?




Ben

[willakawill]

Hi Ben
In your assignment,
cell1 = cell2
you would not use a copy constructor. You would overload the '=' operator.

[benfly08]

Hi Ben
In your assignment,
cell1 = cell2
you would not use a copy constructor. You would overload the '=' operator.

Yep. Actually, I just figure out how i could write the copy constructor.

Public Class testCell
    Private _name As String
    Private isCopied As Boolean
 
    Public Property Name() As String
        Get
            Return _name
        End Get
        Set(ByVal Value As String)
            _name = Value
        End Set
    End Property
 
    Public Property isCopy() As Boolean
        Get
            Return isCopied
        End Get
        Set(ByVal Value As Boolean)
            isCopied = Value
        End Set
    End Property
 
    Public Sub Reset()
        _name = ""
        isCopied = False
    End Sub
 
    Public Sub New()
        _name = ""
        isCopied = False
    End Sub
 
    Public Sub New(ByVal cell As testCell)
        _name = cell.Name
        isCopied = cell.isCopy
    End Sub
End Class
 

Now, in my main program

 
        Dim cell1 As testCell = New testCell
        Dim cell2 As testCell = New testCell
 
        cell2.Name = "Ben"
        cell1 = New testCell(cell2)
        cell2.Name = "William"
 
        If cell1.Name = "William" Then
            MsgBox("Object is referenced")
        End If
 
 

Running this main program, the message box will not pop up. And that's exactly what i want.

[willakawill]

Yep. Actually, I just figure out how i could write the copy constructor.

Public Class testCell
    Private _name As String
    Private isCopied As Boolean
 
    Public Property Name() As String
        Get
            Return _name
        End Get
        Set(ByVal Value As String)
            _name = Value
        End Set
    End Property
 
    Public Property isCopy() As Boolean
        Get
            Return isCopied
        End Get
        Set(ByVal Value As Boolean)
            isCopied = Value
        End Set
    End Property
 
    Public Sub Reset()
        _name = ""
        isCopied = False
    End Sub
 
    Public Sub New()
        _name = ""
        isCopied = False
    End Sub
 
    Public Sub New(ByVal cell As testCell)
        _name = cell.Name
        isCopied = cell.isCopy
    End Sub
End Class
 

Now, in my main program

 
        Dim cell1 As testCell = New testCell
        Dim cell2 As testCell = New testCell
 
        cell2.Name = "Ben"
        cell1 = New testCell(cell2)
        cell2.Name = "William"
 
        If cell1.Name = "William" Then
            MsgBox("Object is referenced")
        End If
 
 

Running this main program, the message box will not pop up. And that's exactly what i want.

You are using a default copy constructor which can lead to unpredictable results

[benfly08]

You are using a default copy constructor which can lead to unpredictable results

But other than that, what could i do?

[willakawill]

But other than that, what could i do?

You write a sub and pass the two instances by ref