Can gift cards be stolen using the card's barcode?

For example, with grocery store gift cards, there's nothing to scratch off or anything else. Just a barcode on the back that's activated upon purchase. Now, suppose someone simply adds the barcode to a mobile wallet on their phone without purchasing the card and waits until someone buys and activates the card. Couldn't that person then "steal" the money and buy anything with the barcode on the card now on their phone?