UIActivityIndicatorView stops animating after app for widget and resumes?

I have a download method that downloads audio with some other data. The download task takes longer. At the beginning of this method, I start UIActivityIndicator

by using a class method NSThread

. UIActivityIndicator

starts animation.

But my problem is to keep the application to a minimum. The app goes into the background and after resuming the app, an activity indicator with no animation is displayed. Sometimes the application crashes.

Does anyone know what the problem is?