tvos – 如何使用preferredFocusEnvironments for preferredFocusedView for ios 10？

我做的是如下：

@IBOutlet weak var viewTemp: UIView!
override var preferredFocusEnvironments : [UIFocusEnvironment] {
    //Condition
    return [viewTemp]
}

这是一个问题.

override weak var preferredFocusedView: UIView? {
    //Condition
    return viewTemp
}