Power down: Improve battery consumption

8:02 - Create a CADisplayLink

// Create a display link

func createDisplayLink() {
   let displayLink = CADisplayLink(target: self, selector: #selector(step))

    // Configure your desired refresh rate by calling preferredFrameRateRange
    displayLink.preferredFrameRateRange = CAFrameRateRange(minimum: 10,
                                                           maximum: 60,
                                                           preferred: 30)

// then activate your CADisplayLink by adding it to the main runloop.
    displayLink.add(to: .current, forMode: .defaultRunLoopMode)
}

16:03 - Discretionary URLSession

// Set up background URL session 
let config = URLSessionConfiguration.background(withIdentifier: "com.app.attachments") 
let session = URLSession(configuration: config, delegate: ..., delegateQueue: ...) 

// Set discretionary 
config.isDiscretionary = true

// Set timeout intervals
config.timeoutIntervalForResource = 24 * 60 * 60 
config.timeoutIntervalForRequest = 60 

// Create request and task 
var request = URLRequest(url: url) 
request.addValue("...", forHTTPHeaderField: "...") 
let task = session.downloadTask(with: request) 

// Set time window of two hours
task.earliestBeginDate = Date(timeIntervalSinceNow: 2 * 60 * 60) 

// Set workload size 
task.countOfBytesClientExpectsToSend = 160 
task.countOfBytesClientExpectsToReceive = 4096 

task.resume()