在后台线程中使用计时器更新UI

In my app I have a timer that can be up to 5 minutes long. The user can add an element to an array which resets the timer to 5 minutes. When the timer counts town, there's also a UIView which changes its width from 100% of the view to 0% of it in proportion to the timer.In my app I have a timer that can be up to 5 mi