I think that means you're adding too much fruit. Slow down just a little bit and make sure you're burying the scraps about halfway down into the box. That should help control the flies.

If you have a large enough bin and enough bedding in there you could bury the food at one side. Burying it will prevent the flies from laying eggs in it. If there is enough space and the compost heats up there should be enough room for them to crawl to the other side.

You say that you had this bin going for some time and then, suddenly, had an outbreak of fruit flies. That means that the eggs were INTRODUCED TO THE BIN!

1. Have you tried freezing (or microwaving)your food scraps?
2. Do you know that this is Fruit Flies? (or is it Fungus Gnats?)
3. Since the bin is already infested, you should stop feeding it. Don't worry! The worms can live quite some time by processing (and re-processing) what food is already there. After awhile, with no new food scraps being added, the Fruit Fly population should diminish.

I just brought my bin in it had been hit with 20 degree nights a few time after it warmed up the flies came back to life not a lot of them but it wasn't to infested outside either

Fruit flies have a short life span so if you can prevent them from laying new eggs the life cycle will be broken. You want the fruit flies to come out of the bin but not be able to introduce new eggs. They lay eggs under the skin of fruit and veggies. But if you freeze the food scraps it will kill the eggs. Thaw the scraps before feeding the worms.

Then, when feeding bury the scraps under at least 3 inches of shredded paper. It discourages the fruit flies from laying eggs in the bin. I have tried shredded cardboard but it didn't work, probably the air gaps were too big.

I have also found that it helps to lay a sheet of cardboard right on top of the bedding. With just a small gap (1/4 - 1/2 inch) around the outside edges to allow air movement.

An added benefit of placing the cardboard directly on top of the bedding is you can lift the cardboard and often find worms just under the cardboard.