Swift class to manage the UIApplication.networkActivityIndicatorVisible in an effective and simple way

NetworkActivityIndicatorManager.swift

//
//  NetworkActivityIndicatorManager.swift
//
//  Created by Mathijs Kadijk on 30-10-14.
//  From: https://gist.github.com/ab1b9196c99dcc16e5fe
//  License: Public domain
//

@objc
class NetworkActivityIndicatorManager {
  private var activityCount: Int
  private var activityIndicatorVisibilityTimer: NSTimer?

  var isNetworkActivityIndicatorVisible: Bool {
    return activityCount > 0
  }

  init() {
    activityCount = 0
  }

  func increment() {
    objc_sync_enter(self)
    activityCount++
    objc_sync_exit(self)

    dispatch_async(dispatch_get_main_queue()) {
      self.updateNetworkActivityIndicatorVisibilityDelayed()
    }
  }

  func decrement() {
    objc_sync_enter(self)
    activityCount = max(activityCount - 1, 0)
    objc_sync_exit(self)

    dispatch_async(dispatch_get_main_queue()) {
      self.updateNetworkActivityIndicatorVisibilityDelayed()
    }
  }

  private func updateNetworkActivityIndicatorVisibilityDelayed() {
    // Delay hiding of activity indicator for a short interval, to avoid flickering
    if (isNetworkActivityIndicatorVisible) {
      dispatch_async(dispatch_get_main_queue()) {
        self.updateNetworkActivityIndicatorVisibility()
      }
    } else {
      activityIndicatorVisibilityTimer?.invalidate()
      activityIndicatorVisibilityTimer = NSTimer(timeInterval: 0.2, target: self, selector: "updateNetworkActivityIndicatorVisibility", userInfo: nil, repeats: false)
      activityIndicatorVisibilityTimer!.tolerance = 0.2
      NSRunLoop.mainRunLoop().addTimer(activityIndicatorVisibilityTimer!, forMode: NSRunLoopCommonModes)
    }
  }

  func updateNetworkActivityIndicatorVisibility() {
    UIApplication.sharedApplication().networkActivityIndicatorVisible = isNetworkActivityIndicatorVisible
  }
}