Resources for Working Less in the Background

applicationWillResignActive: in UIApplicationDelegate Protocol Reference

applicationDidEnterBackground: in UIApplicationDelegate Protocol Reference

applicationWillEnterForeground: in UIApplicationDelegate Protocol Reference

applicationDidBecomeActive: in UIApplicationDelegate Protocol Reference

beginBackgroundTaskWithExpirationHandler: in UIApplication Class Reference

endBackgroundTask: in UIApplication Class Reference

Resources for Prioritizing Work with Quality of Service Classes (QoS)

Concurrency Programming Guide

Grand Central Dispatch (GCD) Reference

NSOperation Class Reference

NSOperationQueue Class Reference

NSThread Class Reference

Testing with Xcode

General Networking Resources

Networking Overview

Resources for Handling Network Errors

Reachability sample code

Restrict Cellular Networking Correctly in Networking Overview

SCNetworkReachability Reference

Resources for Background Networking

NSURL Class Reference

NSURLRequest Class Reference

NSURLSession Class Reference

NSURLSessionConfiguration Class Reference

NSURLSessionDownloadTask Class Reference

NSURLSessionDataDelegate Protocol Reference

NSURLSessionDelegate Protocol Reference

NSURLSessionDownloadDelegate Protocol Reference

NSURLSessionTaskDelegate Protocol Reference

Resources for VoIP

Apple Developer Member Center (for requesting VoIP Services certificates)

PushKit Framework Reference

Resources for Avoiding Extraneous Graphics and Animations

Graphics and Animation in iOS Human Interface Guidelines

Metal Framework Reference

Metal Functions Reference

Metal Programming Guide

Scene Kit Framework Reference

Scene Kit Functions Reference

SpriteKit Framework Reference

SpriteKit Programming Guide

View Programming Guide for iOS

Resources for Restricting UI When Playing Full Screen Video

MPMoviePlayerController Class Reference

Multimedia Programming Guide

General Resources

Debug Your App in Xcode Overview

Instruments User Guide

Testing with Xcode

Performance Testing

Performance Overview