"in a while" is usually refers to the future...or a small amount of time "for a while" usually refers to a longer time frame and talks about the past tense

Hi Maquro, " for a while" means for a short time .When you use it in a sentence it refers to actions that last for a short period of time or to an activity being frequented for a short time as well. In your example " but it's been a while since i watched last time". I am not sure if you ask whether it is possible to substitute " a while " with " for a while" or you want to rephrase the whole sentence using either " for a while" or "in a while"?? Anyways you can neither use "for a while" nor " in a while" as a substitution for " a while " in the previous example. If you changed your sentence you could say : I enjoy watching TV, but I didn't watch it for a while now. That means some short time passed from the time I used to watch TV frequently until now ,during that period I didn't watch it. " in a while " means in a short time , soon . It can't be used in the context of your example. But you could use instead: " Some while ago" : Some while ago I enjoyed watching TV ,but it has been some time I didn't watch it . " all the while" I enjoy watching TV all the while , but it has been a while since i watched last time.

I agree. In this situation, I would say - "It has been a while since I watched TV" But if you want to use "in a while" or "for a while"... In a while - I will watch TV in a while (I am not watching it yet but I will soon) For a while - I will watch TV for a while (I will watch TV for an indefinite period of time). I have been watching TV for a while and I am really enjoying it. In a while I will have to stop and do some English homework!