Xcode 11•Swift 5.1

首先只需启用电池监控：

UIDevice.current.isBatteryMonitoringEnabled = true

然后，您可以创建一个计算属性以返回电池电量：

电池电量从0.0（完全放电）到1.0（100％充电）。访问此属性之前，请确保已启用电池监视。如果未启用电池监视，则电池状态为UIDevice.BatteryState.unknown，此属性的值为–1.0。

var batteryLevel: Float { UIDevice.current.batteryLevel }

要监视设备的电池电量，您可以添加观察者 UIDevice.batteryLevelDidChangeNotification：

NotificationCenter.default.addObserver(self, selector: #selector(batteryLevelDidChange), name: UIDevice.batteryLevelDidChangeNotification, object: nil)

@objc func batteryLevelDidChange(_ notification: Notification) {
    print(batteryLevel)
}

您还可以验证电池状态：

var batteryState: UIDevice.BatteryState { UIDevice.current.batteryState }

case .unknown   //  "The battery state for the device cannot be determined."
case .unplugged //  "The device is not plugged into power; the battery is discharging"
case .charging  //  "The device is plugged into power and the battery is less than 100% charged."
case .full      //   "The device is plugged into power and the battery is 100% charged."

并添加观察者UIDevice.batteryStateDidChangeNotification：

NotificationCenter.default.addObserver(self, selector: #selector(batteryStateDidChange), name: UIDevice.batteryStateDidChangeNotification, object: nil)

@objc func batteryStateDidChange(_ notification: Notification) {
    switch batteryState {
    case .unplugged, .unknown:
        print("not charging")
    case .charging, .full:
        print("charging or full")
    }
}