Proper threading

I have a question about what should and shouldn't be done cross-threads. Essentially I want to know if it is safe to change values created in one thread from another thread. Consider my following code:

Code:

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public void AddCardToAnimate(Card aCard, int aNewX, int aNewY, bool aFlip)
{
        aCard.SetAnimationValues(aNewX, aNewY, aFlip);

        _cards.Add(aCard);

        if(_cards.Count == 1)
        {
                AnimationDelegate ad = new AnimationDelegate(AnimateCards);

                ad.BeginInvoke(null, ad);
        }
}

private void AnimateCards()
{       
        // While there are still cards to be animated
        while(_cards.Count!=0)
        {
                // Get the first card in the array
                Card animatingCard = (Card)_cards[0];

                // Ensure that the card being animated can be seen
                animatingCard.Visible = true;

                // Animate the card
                MoveCard(animatingCard);

                // Remove the card from the "to be animated" array
                    _cards.RemoveAt(0);
        }
}

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I know it might be confusing to know what's going on, but _cards was created in the main thread and many properties accessed within the MoveCard method were also created in the main thread.

Is this ok? Do I either need to encapsulate all of the properties that are being changed into one thread, or have many delegates?

The program seems to work fine this way...but I just want to know the proper way to go about it, and I'm a bit confused with the whole threading thing.

Ok, I think I am less confused now - but still confused.

I originally thought I had read that you should only access objects in the thread they were created.

Apparantly that isn't correct and by using the Monitor object I can ensure everything runs smoothly...

The Monitor classes Enter and Exit methods place a lock on the method the thread calls, so the data doesn't get out of sych.
Another option is to use the SyncLock block (VB.NET) or lock (C#).

Example:

VB Code:

SyncLock
   'code here
End SyncLock

C#

Code:

---

lock(this)
{
  code here
}

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