Class1 = Class2 I want an actual copy

[kevinheeney]

VB.NET

 

Hello,

I am having a problem with copying one class into another. In the following example (a much more detailed example is attached) I have declared to instances of the same class.

When I Make one = another they become linked. So if I change TopClass at all BottomClass changes as well. I don't want BottomClass to be a reference to TopClass, I just want to copy the data as it is at that instant.

 

 

 

Dim TopClass As New Class1

Dim BottomClass As New Class1

 

 

BottomClass = TopClass

 

 

But I don't want to go through and do...

 

BottomClass.First = TopClass.First

BottomClass.Last= TopClass.Last

 

which would keep that from happening.

 

Kevin

classcopy.zip

Edited December 16, 2003 by kevinheeney

[dynamic_sysop]

here's a sample class i knocked up ...

Public Class Class1
   Public intValue As Integer = 0

   Public Sub setValue(ByVal x As Integer)
       intValue = x
   End Sub

   Public Sub CheckValue()
       MessageBox.Show(intValue.ToString())
   End Sub

End Class

then in your form....

   Private cls1 As New Class1() '/// make this one new.
   Private cls2 As Class1 '/// but not this one.

   Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
       cls1.setValue(1500)
       cls2 = DirectCast(cls1, Class1) '/// cls2 is now a copy of cls1
   End Sub

   Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
       If Not cls2 Is Nothing Then
           cls2.CheckValue()
       End If
   End Sub

[koschins]

Clone

 

I think you are looking for the MemberwiseClone() function that creates a shallow copy of the current object. See MSDN for the method System.Object.MemberwiseClone()

[Kurt]

You could overload the constructor of your class to create a copy-constructor. It would take an object of the same type as parameter and then copy the state of the object passed to the newly created object.

 

Public Class cl1

   Public Sub New()
   End Sub

   Public Sub New(ByVal first As Integer, ByVal second As Integer)
       Me.someValue1 = first
       Me.someValue2 = second
   End Sub

   'The Copy-constructor
   Public Sub New(ByVal toCopy As cl1)
       Me.someValue1 = toCopy.someValue1
       Me.someValue2 = toCopy.someValue2
   End Sub

   Public Overrides Function ToString() As String
       Return "(" + Me.someValue1.ToString() + "," + Me.someValue2.ToString() + ")"
   End Function

   Private someValue1 As Integer
   Private someValue2 As Integer

End Class

Public Class Tester

   Public Shared Sub Main()
       Dim obj1 = New cl1(2, 3)
       Dim obj2
       obj2 = New cl1(obj1)

       Console.WriteLine(obj1.ToString())
       Console.WriteLine(obj2.ToString())

   End Sub

End Class