Power Management
================

It is important to know the power state of the scanner as it is for the
host to make sure it does not need to be recharged during the time the scanner
is needed and the operation has a chance to change batteries or charge the scanner.

The application can check the battery level of the scanner using Capture SDK.
Additionally, many Socket Mobile scanners support battery level change notification.

Following are some examples on how to configure the scanner for these features.


Reading the Battery Level
^^^^^^^^^^^^^^^^^^^^^^^^^
Here is example code showing how to request the scanner battery level
information::

  if let device = lastDevice as CaptureHelperDevice! {
      device.getBatteryLevelWithCompletionHandler({ (result :SKTResult, battery: UInt?) in
          print("getting the battery level returned \(result.rawValue)")
          if result == SKTCaptureErrors.E_NOERROR {
              if let level = battery as UInt! {
                  let percentage = SKTHelper.getCurrentLevel(fromBatteryLevel: Int(level))
                  print("battery level: \(percentage)%")
              }
          }
      })
  }

The ``lastDevice`` is a ``CaptureHelperDevice`` instance that has been set in the
``didNotifyArrivalForDevice`` delegate.

Set up the Battery Level Change Notification
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
Setting up the scanner to make it send a notification each time the battery
level changes is a 2 step process. Since this setting is persistent in the
scanner, the first time the scanner connects to the application we query the
notification setting, if the battery level change notification is not activated
then we activate it.
The initial battery level needs to be read at this time because it could take a long
time before the first battery level change notification is received.
::

  device.getNotificationsWithCompletionHandler({ (result: SKTResult, notifications: SKTCaptureNotifications?) in
      print("getting notifications returned \(result.rawValue)")
      if result == SKTCaptureErrors.E_NOERROR {
          if var currentNotification = notifications as SKTCaptureNotifications! {
              if !currentNotification.contains(.batteryLevelChange) {
                  print("adding the battery level change notification")
                  currentNotification.insert(.batteryLevelChange)
                  device.setNotifications(currentNotification, withCompletionHandler: { (result: SKTResult) in
                      print("changing notification to battery level change returned \(result.rawValue)")
                  })
              } else {
                  print("the battery level change notification is already set")
              }
          }
      }
  })


The ``device`` is a ``CaptureHelperDevice`` instance that has been received in the
argument of the ``didNotifyArrivalForDevice`` delegate.

Notice that we also use this ``didNotifyArrivalForDevice`` delegate to ask for the
current battery level so it can be displayed right away.

In order to receive the battery level change notifications, we need to derive the
class from the ``CaptureHelperDevicePowerDelegate`` protocol and provide a handler
for the ``didChangeBatteryLevel`` delegate::

  func didChangeBatteryLevel(_ batteryLevel: Int, forDevice device: CaptureHelperDevice){
      print("new battery level: \(SKTHelper.getCurrentLevel(fromBatteryLevel: Int(batteryLevel)))%")
  }

.. note::
   The ``CaptureHelperDevicePowerDelegate`` protocol also has a ``didChangePowerState``
   delegate that could be left empty if not required by the application.


Power State Change and other Events
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
The same principle can be followed for the other events of the device, such as
the ``didChangePowerState`` delegate which notifies the application each time
the scanner is plugged into a power source, or unplugged or dropped in the
charger cradle.

Other events such as buttons state can be tracked by deriving from the
``CaptureHelperDeviceButtonsDelegate`` protocol and by implementing its
``didChangeButtonsState`` delegate.