Dang those gnats!!

We have gnats or fruit flies everywhere. They just appeared one day when we were cooking out. Stephen had just cut a whole cantalope and had it in a bowl on the bar. We went outside for 0.5 seconds to turn the burgers and we came in and to our surprise the cantalope was completely covered w/ gnats. I mean it looked like we had put pepper on it!!! I died! We threw it away and the gnats have not left. Does anyone have any suggestions?