Why does the instance change?

[Daniel]

Hey guys

I have an instance of an object say:

List<Object> myList = new List<Object>();

Object myObject = new Object();
myObject.Positi onVector = new Vector3(10,10,1 0);

myList.Add(myOb ject);
With the above code as an accurate example i do that in a loop. And on each
iteration i change the position vector, however when i do this and check my
list it has correctly added each new instance as a separate entry but they
all have the position of the last one to be added. When i steped through it
in debug this was verified, the correct positon details are in on one
iteration and on the next iteration immediately after the new instance has
its position changed so too does the one already in my List.

I presume that a new memory allocation isn't being made and so on setting
position it overwrites the same memory my list is looking at but why? I
thought the 'new' operator explicitly tells it to create a new memory
allocation? Am i missing something? Anyone know how i can prevent this
situation.

Thanks

[sb]

Although I think I understand what you're saying, I'd like to see the actual
code. Hopefully you can trim things down enough to post a short sample that
demonstrates the problem.

-sb
"Daniel" <Da*****@vestry online.com> wrote in message
news:Oz******** ******@TK2MSFTN GP05.phx.gbl...

Hey guys

I have an instance of an object say:

List<Object> myList = new List<Object>();

Object myObject = new Object();
myObject.Positi onVector = new Vector3(10,10,1 0);

myList.Add(myOb ject);
With the above code as an accurate example i do that in a loop. And on
each iteration i change the position vector, however when i do this and
check my list it has correctly added each new instance as a separate entry
but they all have the position of the last one to be added. When i steped
through it in debug this was verified, the correct positon details are in
on one iteration and on the next iteration immediately after the new
instance has its position changed so too does the one already in my List.

I presume that a new memory allocation isn't being made and so on setting
position it overwrites the same memory my list is looking at but why? I
thought the 'new' operator explicitly tells it to create a new memory
allocation? Am i missing something? Anyone know how i can prevent this
situation.

Thanks

[Greg Young]

I am not understanding some of your explanation ...

can you also post the definition of "Object" does it by chance have
positionvector declared as a static field ?

Cheers,

Greg
"Daniel" <Da*****@vestry online.com> wrote in message
news:Oz******** ******@TK2MSFTN GP05.phx.gbl...

Hey guys

I have an instance of an object say:

List<Object> myList = new List<Object>();

Object myObject = new Object();
myObject.Positi onVector = new Vector3(10,10,1 0);

myList.Add(myOb ject);
With the above code as an accurate example i do that in a loop. And on
each iteration i change the position vector, however when i do this and
check my list it has correctly added each new instance as a separate entry
but they all have the position of the last one to be added. When i steped
through it in debug this was verified, the correct positon details are in
on one iteration and on the next iteration immediately after the new
instance has its position changed so too does the one already in my List.

I presume that a new memory allocation isn't being made and so on setting
position it overwrites the same memory my list is looking at but why? I
thought the 'new' operator explicitly tells it to create a new memory
allocation? Am i missing something? Anyone know how i can prevent this
situation.

Thanks

[Daniel]

Well thats just the point, it doesnt make sense to me either. The Object bit
i gave was just an example but an accurate one, here's a real one:

List<myClass> myList = new List<myClass>() ;

for(int i=0; i<10; i++)
{
myClass myObject = new Object();
myObject.Positi onVector = new Vector3(10 + (i*3),10 + (i*5),10);

myList.Add(myOb ject);
}
And no nothing is static.

So as i said if were to debug and look at what is on myList it goes like
this

on first iteration:

myObject.Positi on = 10,10,10

on second iteration just before the Add myObject.Positi on = 13, 15, 10
then once added, myList now has 2 entries, but both have position 13,15,10.

So my question is, is there something about List that i don't know of to
explain how the first instance put on the list could be effected by the
second?

thanks
"Greg Young" <Dr************ *@hotmail.com> wrote in message
news:u0******** ******@TK2MSFTN GP02.phx.gbl...

I am not understanding some of your explanation ...

can you also post the definition of "Object" does it by chance have
positionvector declared as a static field ?

Cheers,

Greg
"Daniel" <Da*****@vestry online.com> wrote in message
news:Oz******** ******@TK2MSFTN GP05.phx.gbl...

Hey guys

I have an instance of an object say:

List<Object> myList = new List<Object>();

Object myObject = new Object();
myObject.Positi onVector = new Vector3(10,10,1 0);

myList.Add(myOb ject);
With the above code as an accurate example i do that in a loop. And on
each iteration i change the position vector, however when i do this and
check my list it has correctly added each new instance as a separate
entry but they all have the position of the last one to be added. When i
steped through it in debug this was verified, the correct positon details
are in on one iteration and on the next iteration immediately after the
new instance has its position changed so too does the one already in my
List.

I presume that a new memory allocation isn't being made and so on setting
position it overwrites the same memory my list is looking at but why? I
thought the 'new' operator explicitly tells it to create a new memory
allocation? Am i missing something? Anyone know how i can prevent this
situation.

Thanks

[Joanna Carter [TeamB]]

"Daniel" <Da*****@vestry online.com> a écrit dans le message de news:
Og************* *@TK2MSFTNGP04. phx.gbl...

| Well thats just the point, it doesnt make sense to me either. The Object
bit
| i gave was just an example but an accurate one, here's a real one:
|
| List<myClass> myList = new List<myClass>() ;
|
| for(int i=0; i<10; i++)
| {
| myClass myObject = new Object();
| myObject.Positi onVector = new Vector3(10 + (i*3),10 + (i*5),10);
|
| myList.Add(myOb ject);
| }
| And no nothing is static.

1. You have not shown the declaration of myClass.
2. Your example instantiates Object into a myClass reference

This code is not complete enough to see if you have declared PositionVector
as static, which is the most likely cause of your problem.

Could you post a *complete* but *brief* and *compiling* example.

Joanna

--
Joanna Carter [TeamB]
Consultant Software Engineer

[Greg Young]

Ok you are going to need to be clearer ... this code works fine.

class PositionVector

{

public int x, y, z;

public PositionVector( int _x, int _y, int _z)

{

x = _x;

y = _y;

z = _z;

}

public override string ToString()

{

return this.x.ToString () + ":" + this.y.ToString () + ":" +
this.z.ToString ();

}

}

class myClass

{

public PositionVector PositionVector;

}

class Program

{

static void Main(string[] args)

{

List<myClass> myList = new List<myClass>() ;

for (int i = 0; i < 10; i++)

{

myClass myObject = new myClass();

myObject.Positi onVector = new PositionVector( 10 + (i * 3), 10 + (i * 5),
10);

myList.Add(myOb ject);

}

foreach (myClass c in myList)

{

Console.WriteLi ne(c.PositionVe ctor.ToString() );

}

}

}

"Daniel" <Da*****@vestry online.com> wrote in message
news:Og******** ******@TK2MSFTN GP04.phx.gbl...

Well thats just the point, it doesnt make sense to me either. The Object
bit i gave was just an example but an accurate one, here's a real one:

List<myClass> myList = new List<myClass>() ;

for(int i=0; i<10; i++)
{
myClass myObject = new Object();
myObject.Positi onVector = new Vector3(10 + (i*3),10 + (i*5),10);

myList.Add(myOb ject);
}
And no nothing is static.

So as i said if were to debug and look at what is on myList it goes like
this

on first iteration:

myObject.Positi on = 10,10,10

on second iteration just before the Add myObject.Positi on = 13, 15, 10
then once added, myList now has 2 entries, but both have position
13,15,10.

So my question is, is there something about List that i don't know of to
explain how the first instance put on the list could be effected by the
second?

thanks
"Greg Young" <Dr************ *@hotmail.com> wrote in message
news:u0******** ******@TK2MSFTN GP02.phx.gbl...

I am not understanding some of your explanation ...

can you also post the definition of "Object" does it by chance have
positionvector declared as a static field ?

Cheers,

Greg
"Daniel" <Da*****@vestry online.com> wrote in message
news:Oz******** ******@TK2MSFTN GP05.phx.gbl...

Hey guys

I have an instance of an object say:

List<Object> myList = new List<Object>();

Object myObject = new Object();
myObject.Positi onVector = new Vector3(10,10,1 0);

myList.Add(myOb ject);
With the above code as an accurate example i do that in a loop. And on
each iteration i change the position vector, however when i do this and
check my list it has correctly added each new instance as a separate
entry but they all have the position of the last one to be added. When i
steped through it in debug this was verified, the correct positon
details are in on one iteration and on the next iteration immediately
after the new instance has its position changed so too does the one
already in my List.

I presume that a new memory allocation isn't being made and so on
setting position it overwrites the same memory my list is looking at but
why? I thought the 'new' operator explicitly tells it to create a new
memory allocation? Am i missing something? Anyone know how i can prevent
this situation.

Thanks

[Göran Andersson]

No, sorry, the code you show is *not* an accurate example. If you can't
show the actual code you are using, you have to at least show a complete
example that will actually show the problem you are talking about.

It's near to impossible to locate an error in a code by looking at some
other code that doesn't even have the error in it.

Think of it as going to your local mecanic, show him a picture of your
bike, and ask him why you car is not starting... ;)

Daniel wrote:

Hey guys

I have an instance of an object say:

List<Object> myList = new List<Object>();

Object myObject = new Object();
myObject.Positi onVector = new Vector3(10,10,1 0);

myList.Add(myOb ject);
With the above code as an accurate example i do that in a loop. And on each
iteration i change the position vector, however when i do this and check my
list it has correctly added each new instance as a separate entry but they
all have the position of the last one to be added. When i steped through it
in debug this was verified, the correct positon details are in on one
iteration and on the next iteration immediately after the new instance has
its position changed so too does the one already in my List.

I presume that a new memory allocation isn't being made and so on setting
position it overwrites the same memory my list is looking at but why? I
thought the 'new' operator explicitly tells it to create a new memory
allocation? Am i missing something? Anyone know how i can prevent this
situation.

Thanks

[Daniel]

Ok my apologies here is the exact code,

On my external class that calls the code withina loop.

PlayingCard theCardSceneObj = new PlayingCard();

theCardSceneObj = (PlayingCard)_o bjMan.GetObject ((int)ObjectID. Cards);

theCardSceneObj .SetCardFrame(p layer.Hand[j]);

theCardSceneObj .FaceUp = player.Hand[j].ShowState;

theCardSceneObj .IsVisible = true;

theCardSceneObj .Position = new Vector3(seatPos .X + (j * 15), seatPos.Y + (j
* 10), 0);

_objMan.AddToRe nderList(theCar dSceneObj);

Inside the_objMan instance:

class ObjectManager

{

List<SceneObjec t> _sceneObjList;

List<SceneObjec t> __renderList;

public ObjectManager()

{

_sceneObjList = new List<SceneObjec t>();

}

public void AddToRenderList (SceneObject so)
{
_renderList.Add (so);
}

public object GetObject(int ObjectId)

{

int count = 0;

foreach (SceneObject so in _sceneObjList)

{

if (so.ObjectID == ObjectId)

return _sceneObjList[count];

count++;

}

return null;

}
That any clearer?

"Göran Andersson" <gu***@guffa.co m> wrote in message
news:u1******** ******@TK2MSFTN GP03.phx.gbl...

No, sorry, the code you show is *not* an accurate example. If you can't
show the actual code you are using, you have to at least show a complete
example that will actually show the problem you are talking about.

It's near to impossible to locate an error in a code by looking at some
other code that doesn't even have the error in it.

Think of it as going to your local mecanic, show him a picture of your
bike, and ask him why you car is not starting... ;)

Daniel wrote:

Hey guys

I have an instance of an object say:

List<Object> myList = new List<Object>();

Object myObject = new Object();
myObject.Positi onVector = new Vector3(10,10,1 0);

myList.Add(myOb ject);
With the above code as an accurate example i do that in a loop. And on
each iteration i change the position vector, however when i do this and
check my list it has correctly added each new instance as a separate
entry but they all have the position of the last one to be added. When i
steped through it in debug this was verified, the correct positon details
are in on one iteration and on the next iteration immediately after the
new instance has its position changed so too does the one already in my
List.

I presume that a new memory allocation isn't being made and so on setting
position it overwrites the same memory my list is looking at but why? I
thought the 'new' operator explicitly tells it to create a new memory
allocation? Am i missing something? Anyone know how i can prevent this
situation.

Thanks

[Jon Skeet [C# MVP]]

Daniel <Da*****@vestry online.com> wrote:

Ok my apologies here is the exact code,
<snip>
That any clearer?

Not a lot. You still haven't provided a short but complete example
which demonstrates the problem. Something we can compile and run.

See http://www.pobox.com/~skeet/csharp/complete.html

(You may well find the problem while trying to come up with a short but
complete example.)

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too

[Daniel]

This goes through one huge class, which calls another class which is
inherited down from two more. Its impossbile to show a complete example.
Hence my original shortened version that showed only the parts needed to
recreate my problem. Ok i will sort this one out for myself, thanks anyway.

"Jon Skeet [C# MVP]" <sk***@pobox.co m> wrote in message
news:MP******** *************** *@msnews.micros oft.com...

Daniel <Da*****@vestry online.com> wrote:

Ok my apologies here is the exact code,

<snip>

That any clearer?

Not a lot. You still haven't provided a short but complete example
which demonstrates the problem. Something we can compile and run.

See http://www.pobox.com/~skeet/csharp/complete.html

(You may well find the problem while trying to come up with a short but
complete example.)

--
Jon Skeet - <sk***@pobox.co m>
http://www.pobox.com/~skeet Blog: http://www.msmvps.com/jon.skeet
If replying to the group, please do not mail me too