ArrayList Question

  • Thread starter Thread starter george r smith
  • Start date Start date
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george r smith

I am trying to create an arrayList that contains multiple arrayLists.
My code attempt is below. The question I have is how can I get away
from creating another pAttribute list than can be added to pItem.

As I understand it (and I coded it to test) if I try to use pAttribute again
by clearing with pAttribute.Clear because it is a shallow copy the
pItem[0] is also cleared. I guess I need a "deep copy" but can't find
any documentation on it.

So is there any way to pItem[1].Add({100.00,200.00}). This will not compile
but
it shows what I want to do.

I might add that I want to use ArrayList because you are not restricted to
one type
as in arrays.


thanks
grs


static void Main(string[] args)
{
ArrayList pItem = new ArrayList();
ArrayList pAttribute = new ArrayList();
for (int i = 101; i < 105; i++)
{
pAttribute.Add(i);
}
pItem.Add(pAttribute);
PrintValues((ArrayList)pItem[0]);
}

public static void PrintValues(ArrayList myList)
{
IEnumerator myEnumerator = myList.GetEnumerator();
while (myEnumerator.MoveNext())
Console.WriteLine(myEnumerator.Current);
}
}
 
There are a few ways.

If you want to follow your suggested attempt, you might need to initialize
the array like so -- .Add(new int[]{100.00, 200.00}).

Alternatively, you could like into using the ArrayList.CopyTo(...) method.

Or try the Object.MemberwiseClone(...) since you are really only interested
in preserving pAttribute, this might be sufficient.
 
If you want to use pAttribute again without trashing the ArrayList you've
already created just do:

pAttribute = new ArrayList();

The pAttribute reference will now point to a *different* ArrayList and your
old ArrayList will still be intact and won't be garbage collected because
it's referenced by pItem[0] (note: if you then null pItem then your old
ArrayList will be now eligible for garbage collection).
As you pointed out pAttribute.Clear() will clear pItem[0] because they are
both references to the SAME object, you didn't make a copy at all and you
probably don't want to (whether you know it or not).
As for using ArrayList instead of arrays, you are wrong about arrays. An
object[] array can contain a mix of whatever items you want since all
classes inherit from object. So if you don't need the dynamic resizing
abilities of the ArrayList, you're better off with object[].
 
Matt,
Thanks for the info on object[] array - now that you have told me I
understand :).
I do need dynamic so I will keep on the ArrayList. Thanks again.
grs

Matt Burland said:
If you want to use pAttribute again without trashing the ArrayList you've
already created just do:

pAttribute = new ArrayList();

The pAttribute reference will now point to a *different* ArrayList and your
old ArrayList will still be intact and won't be garbage collected because
it's referenced by pItem[0] (note: if you then null pItem then your old
ArrayList will be now eligible for garbage collection).
As you pointed out pAttribute.Clear() will clear pItem[0] because they are
both references to the SAME object, you didn't make a copy at all and you
probably don't want to (whether you know it or not).
As for using ArrayList instead of arrays, you are wrong about arrays. An
object[] array can contain a mix of whatever items you want since all
classes inherit from object. So if you don't need the dynamic resizing
abilities of the ArrayList, you're better off with object[].


george r smith said:
I am trying to create an arrayList that contains multiple arrayLists.
My code attempt is below. The question I have is how can I get away
from creating another pAttribute list than can be added to pItem.

As I understand it (and I coded it to test) if I try to use pAttribute again
by clearing with pAttribute.Clear because it is a shallow copy the
pItem[0] is also cleared. I guess I need a "deep copy" but can't find
any documentation on it.

So is there any way to pItem[1].Add({100.00,200.00}). This will not compile
but
it shows what I want to do.

I might add that I want to use ArrayList because you are not restricted to
one type
as in arrays.


thanks
grs


static void Main(string[] args)
{
ArrayList pItem = new ArrayList();
ArrayList pAttribute = new ArrayList();
for (int i = 101; i < 105; i++)
{
pAttribute.Add(i);
}
pItem.Add(pAttribute);
PrintValues((ArrayList)pItem[0]);
}

public static void PrintValues(ArrayList myList)
{
IEnumerator myEnumerator = myList.GetEnumerator();
while (myEnumerator.MoveNext())
Console.WriteLine(myEnumerator.Current);
}
}
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