1)覆盖canBecomeFocused

2)覆盖“didUpdateFocusInContext：withAnimationCoordinator：”方法,以便能够将细胞突出显示为聚焦

Swift 2.3：

override func canBecomeFocused() -> Bool {
    return true
}
 
override func didUpdateFocusInContext(context: UIFocusUpdateContext,withAnimationCoordinator coordinator: UIFocusAnimationCoordinator) {
 
    if context.nextFocusedView == self {
        coordinator.addCoordinatedAnimations({ () -> Void in
            self.layer.backgroundColor = UIColor.blueColor().colorWithAlphaComponent(0.2).CGColor
        },completion: nil)
    } else if context.prevIoUslyFocusedView == self {
        coordinator.addCoordinatedAnimations({ () -> Void in
            self.layer.backgroundColor = UIColor.clearColor().CGColor
        },completion: nil)
    }
}

斯威夫特3：

override var canBecomeFocused: Bool {
    return true
}
 
override func didUpdateFocus(in context: UIFocusUpdateContext,with coordinator: UIFocusAnimationCoordinator) {
    if context.nextFocusedView == self {
        coordinator.addCoordinatedAnimations({ () -> Void in
            self.layer.backgroundColor = UIColor.blue.withAlphaComponent(0.2).cgColor
        },completion: nil)
 
    } else if context.prevIoUslyFocusedView == self {
        coordinator.addCoordinatedAnimations({ () -> Void in
            self.layer.backgroundColor = UIColor.clear.cgColor
        },completion: nil)
    }
}