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pass objects

Posted on 2009-04-07
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Last Modified: 2013-12-17
I am passing a  list of objects.
I want to change  values in the list.
IS there any problem with this as it is a little  confusing. Am I changing a copy of the list or the actual list ?


obj1 - create list of objects
-----
 Dim missileList As New List(Of ClassMissile)
  Public Property GetMissiles() As List(Of ClassMissile)
        Get
            Return missileList
        End Get
   

    obj2 -get  list and change values
---------

   Dim missiles As List(Of ClassMissile)
        missiles = Sprite.GetMissiles
          For Each Mymissile In missiles
...
mymissile.y=0 'is this changing the list property as i think it should?
----------------------
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Question by:jagguy
7 Comments
 
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Expert Comment

by:oobayly
ID: 24086108
You should be changing the actual list, but the easiest way to test is this:
' Get the list
Dim missiles1 As List(Of ClassMissile) = Sprite.GetMissiles()
 
' Change an item
missiles1(0).y = 123456
 
' Get the list again
Dim missiles2 As List(Of ClassMissile) = Sprite.GetMissiles()
 
' Compare y for the 1st item
Dim b As Boolean = (missiles1(0).y = missiles2(0).y)

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Expert Comment

by:Sreedhar Vengala
ID: 24086134
You are changing acutal list.
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Author Comment

by:jagguy
ID: 24086166

When i pass the list am i passing the whole data around ?

IF I am passing the whole data around i could as well use a public list in a module.
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Expert Comment

by:oobayly
ID: 24086263
Well, technically you're returning a reference to the object data.
As for modules, I'd stay clear of them, and stick with Object Orientated code.
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Expert Comment

by:HarryNS
ID: 24086407
If you need to work with the list that contains value without changing the list, use <your LIst>.CopyTo(Array). This will copy the values to new array. There you can change values and use.
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Accepted Solution

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Mike Tomlinson earned 500 total points
ID: 24088558
"When i pass the list am i passing the whole data around?"

As oobayly stated you are only passing a reference.  Stated differently, you are NOT passing the entire List around...just the pointer to the List (but we don't deal with pointers in managed .Net so they are called "references").  Think of it as passing the key to the front door of a house.  It allows you access to the house without passing the entire house....
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Expert Comment

by:oobayly
ID: 24088583
@Idle_Mind
I like that analogy.
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