Just made a comment on another thread about my win over gnats/fruit flies. Will c/p here:
This comment will get lost in the sea of replies, but here’s my two cents: Never had one method work exclusively. The following three methods combined have eradicated the stinkers from my home completely. It’s not overnight, but drastic differences are noticed in a week or so.
+1 for the vinegar dish soap method. Fruitflies are also attracted to alcohol. Random science bit: Fruit flies prefer to lay their eggs on rotten food that can contain ethanol in as high as 7% concentration. (That’s 14 proof to you bar hoppers.) And just like people, the insects differ in their ability to hold their drinks. 
So, when I have some leftover dregs of makgeoli (a homemade korean rice wine), or wine, I do that in lieu of vinegar and attract a ton more.
Sticky paper. But, I’m not a fan of the sticky yellow cutouts. There are clear ones sold for the window. I find most flying insects congregate there if all the food is away. It’s gross but strangely satisfying when we replace those sticky sheets.
If you have houseplants, they could be breeding in the dirt. There’s a product called “mosquito dunks” that can be found online or at any hardware store- sold as donuts or pellets. The main ingredient is BTI which produces a bacteria toxic to these at larval stage; it’ll kill the fruit flies/gnats/fungal gnats/mosquitos at larval stage . This is human, pet, & even aquarium safe. With these BTI pellets/donuts, I soak overnight in a gallon jug and make a “tea.” I use this when watering my house plants and dump the excess in the drain (completely safe) to get any bugs trying to colonize in the damp pipes.
Hope this helps~
