accessibilityElementDidBecomeFocused dont get called

I´m trying to get the information if an element get focused with voiceover. So i override the accessibilityElementDidBecomeFocused method, but this gets never called. Did i forget something?

override func viewDidLoad() {
    super.viewDidLoad()        
    viewArray.append(UIView())
    viewArray.append(UIView())        
    viewArray[0].frame = CGRectMake(20, 210, 100, 100)
    viewArray[0].isAccessibilityElement = true
    self.view.addSubview(viewArray[0])

    viewArray[1].frame = CGRectMake(220, 220, 100, 100)
    viewArray[1].isAccessibilityElement = true
    self.view.addSubview(viewArray[1])

}

//never called
override func accessibilityElementDidBecomeFocused(){
    println("accessibilityElementDidBecomeFocused")
}