切换选项卡时Swift 2 - EXC_BAD_ACCES

I have a swift 2 app with 2 tabs. On both screens I perform a dataTaskWithUrl in the viewDidAppear, to get the data refreshed when the screen appears. This results, if I keep switching fast between the tabs back and forth, sooner or later I become an EXC_BAD_ACCESS, I suppose because of memory issues. My questions are:I have a swift 2 app with 2 tabs. On both scree