copying an object, not just a reference?

[Dave O]

Hi there,

Here's a pretty basic question about objects for the OO types out there:

How do I copy an object to another object?

For example, I'd like to copy object A to object B, but still maintain them as separate data.

As I understand it, when I do this with the two objects:

B = A

...B now points to the same object as A (i.e. they're both references to the same data instance).

What I want is to *copy* A to B, then be able to change B without affecting A - like what would happen if I was dealing with primitive variables.

Is there an easy way to do this, or do I have to write a copy function for each type of object I'm working with?

Thanks for any help!

 

[Erel]

You can use RandomAccessFile.WriteObject / ReadObject: (untested code)

Sub CopyObject(Obj As Object) As Object
 Dim raf As RandomAccessFile
 raf.Initialize(File.DirInternalCache, "1.dat", false)
 raf.WriteObject(Obj, True, 0)
 Dim newObj As Object
 newObj = raf.ReadObject(0)
 raf.Close
 Return newObj
End Sub

You can keep the temp file open and make raf variable a global variable.

 

[Vader]

Fyi in the .net world, this is referred to as a clone.

B=A.Clone

 

[Erel]

.Net Clone is pretty unusable as it doesn't determine whether it is a shallow clone or a deep clone (like done here).

You can read more about it here: Should we Obsolete ICloneable (The SLAR on System.ICloneable) - Brad Abrams - Site Home - MSDN Blogs

 

[Vader]

.Net Clone is pretty unusable as it doesn't determine whether it is a shallow clone or a deep clone (like done here).

You can read more about it here: Should we Obsolete ICloneable (The SLAR on System.ICloneable) - Brad Abrams - Site Home - MSDN Blogs

Yep. I usually serialize the object down to a text file, then build it back up. Pretty well what I think you do.

edit: When I say "down" I mean all the way to object().

 

[DavideV]

You can use RandomAccessFile.WriteObject / ReadObject: (untested code)

Sub CopyObject(Obj As Object) As Object
Dim raf As RandomAccessFile
raf.Initialize(File.DirInternalCache, "1.dat", false)
raf.WriteObject(Obj, True, 0)
Dim newObj As Object
newObj = raf.ReadObject(0)
raf.Close
Return newObj
End Sub

You can keep the temp file open and make raf variable a global variable.

Thx Erel you saved my time

 

[wonder]

Hi!

Is this, to date, the best way to copy an object?
I'd like to copy an array of objects, say 512.

 

[Erel]

It is better to use B4XSerializator:

Sub CopyObject(o As Object) As Object
   Dim s As B4XSerializator
   Return s.ConvertBytesToObject(s.ConvertObjectToBytes(o))
End Sub

Note that not all types are supported. Supported types are: primitives, strings, lists, maps, arrays of objects or bytes, custom types and any combination of those (a map that holds arrays of custom types).