如何隐藏NSTextFieldCell的焦点环？

override func drawFocusRingMask(withFrame frame: NSRect, in controlView: NSView) {
    NSRectFill(NSRect.zero)
}

override var focusRingMaskBounds: NSRect {
    return NSRect(x: bounds.origin.x, y: bounds.origin.y, width: bounds.width, height: bounds.height - 1)
}

override var focusRingType: NSFocusRingType {
    return .none
}

override var focusRingMaskBounds: NSRect {
    return NSRect(x: bounds.origin.x, y: bounds.origin.y, width: bounds.width, height: bounds.height - 1)
}