观察操作系统:batterystate的swift kvo不工作

我想监视电池状态,所以我为电池状态添加了kvo,如下所示

private func setupNotification() {

    WKInterfaceDevice.current().addObserver(self,
                                            forKeyPath: #keyPath(WKInterfaceDevice.batteryState),
                                            options: [.new],
                                            context: nil)
}

override public func observeValue(forKeyPath keyPath: String?,
                                  of object: Any?,
                                  change: [NSKeyValueChangeKey: Any]?,
                                  context: UnsafeMutableRawPointer?) {
    if keyPath == #keyPath(WKInterfaceDevice.batteryState) {
        switch WKInterfaceDevice.current().batteryState {
        case .charging:
            self.stopMonitoring()
        case .unplugged:
            if BatteryManager.batteryLevel > Constant.Battery.criticalValue {
                self.startMonitoring()
            }
        default:
            break
        }
    }
}

我以前也加过

func enableBatteryMonitoring() {
    WKInterfaceDevice.current().isBatteryMonitoringEnabled = true
}

但当插入/拔出插头充电器时,它不会被调用。 有什么许可证吗?或者我遗漏了什么?