Why am I getting an InvalidOperationException?

Question

So I have a constructor and a method that returns a card. I'm getting an InvalidOperationException for some reason. Anyone can think of anything?

The cards list is not empty, I just removed the card generation algorithm from the constructor here to make it easier to read.

Here's the code:

public Deck()
{
    cards = new List<Card>();
    cardStack = new Stack<Card>();
    // cards list gets populated here
    foreach (Card card in cards)
    {
        cardStack.Push(card);
    }
}

public Card drawCard()
{
    return cardStack.Pop(); // This line is giving me an InvalidOperationException
}

Thanks!

-1. We can't figure out a problem from code that doesn't have it. Please post some code that *adds at least one card* and *reproduces* the problem. Until then, the cards list is empty, and that's the cause. — R. Martinho Fernandes, Apr 16 '11 at 02:19
It is always good to check if the stack is empty before trying to pop. Always. — manojlds, Apr 16 '11 at 02:26

score 1 · Answer 1 · answered Apr 16 '11 at 02:14

1

Chances are that cardStack is empty when you call Pop(). I suggest that you check the number of cards in the stack before you pop it and do something reasonable if the deck is empty.

answered Apr 16 '11 at 02:14

JSBձոգչ

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score 1 · Answer 2 · edited Apr 16 '11 at 02:24

1

Maybe this is a stupid question ... but are you checking the stack is non-empty before you pop it? According to the MS docs that's the only reason this exception should be thrown ...

edited Apr 16 '11 at 02:24

R. Martinho Fernandes

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answered Apr 16 '11 at 02:16

David

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R. Martinho Fernandes · Answer 3 · 2011-04-16T02:29:47.597

You have no cards in there!

You create a new list of cards and that list starts empty. Then you grab them all (read: none) and push them into the stack. You get an empty stack.

And then you try popping, but you can't pop from an empty stack. The InvalidOperationException and the reason ("the Stack<T> is empty") are right there in documentation.

You need to initialize your list of cards by adding some cards. Or maybe just remove the list and initialize the stack directly.

And you also need to make sure you're not popping too much. If you pop all the cards out of the stack, when you pop next, the stack will be empty, and you'll run into the same problem.

score 0 · Answer 4 · answered Apr 16 '11 at 02:14

0

Looking at that code, no cards actually get pushed onto cardStack (cards is initially empty). You're getting the exception because C# is telling you that there's nothing to pop.

answered Apr 16 '11 at 02:14

helloworld922

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He has commented out the cards population part. – manojlds Apr 16 '11 at 02:19

Why am I getting an InvalidOperationException?

4 Answers4