Gwendolyn Weston "While Your App Was Sleeping"

Transcript

1. While Your App Was Sleeping Gwendolyn Weston
 @purpleyay
2. Background Transfer Services keeps requests going even if the app is terminated by the system
3. Motivation
4. A Teakettle • That requires you to stand near it • And watch it in order for it to boil water
5. Where can this happen in our apps?
6. PlanGrid
7. To guarantee download completion • Change device settings so it never locks • Stay on the app
8. Downloading without Background Transfer Services is like watching water boil.
9. Overview • How to download in the foreground • How to make that request background compatible • How to navigate common pitfalls
10. Downloading in the foreground
11. Downloading in Foreground let urlstring = "https://remoteteakettle.com/boiledwater.pdf" let filepath = "Documents/local_teakettle" if let url = NSURL(string: urlstring) { let task = NSURLSession.sharedSession().downloadTaskWithURL(url, completionHandler: { (location:NSURL?, response:NSURLResponse?, error:NSError?) in if let loc = location, path = loc.path { try! NSFileManager.defaultManager().moveItemAtPath(path, toPath:filepath) } }) task.resume() }
12. Downloading in Foreground NSURLSession: vends and manages requests let urlstring = "https://remoteteakettle.com/boiledwater.pdf" let filepath = "Documents/local_teakettle" if let url = NSURL(string: urlstring) { let task = NSURLSession.sharedSession().downloadTaskWithURL(url, completionHandler: { (location:NSURL?, response:NSURLResponse?, error:NSError?) in if let loc = location, path = loc.path { try! NSFileManager.defaultManager().moveItemAtPath(path, toPath:filepath) } }) task.resume() }
13. Downloading in Foreground sharedSession: singleton session with default settings let urlstring = "https://remoteteakettle.com/boiledwater.pdf" let filepath = "Documents/local_teakettle" if let url = NSURL(string: urlstring) { let task = NSURLSession.sharedSession().downloadTaskWithURL(url, completionHandler: { (location:NSURL?, response:NSURLResponse?, error:NSError?) in if let loc = location, path = loc.path { try! NSFileManager.defaultManager().moveItemAtPath(path, toPath:filepath) } }) task.resume() }
14. Downloading in Foreground NSURLSessionDownloadTask: the request let urlstring = "https://remoteteakettle.com/boiledwater.pdf" let filepath = "Documents/local_teakettle" if let url = NSURL(string: urlstring) { let task = NSURLSession.sharedSession().downloadTaskWithURL(url, completionHandler: { (location:NSURL?, response:NSURLResponse?, error:NSError?) in if let loc = location, path = loc.path { try! NSFileManager.defaultManager().moveItemAtPath(path, toPath:filepath) } }) task.resume() }
15. NSURLSessionTask • NSURLSessionDownloadTask • NSURLSessionUploadTask • NSURLSessionDataTask - short-lived requests (not background compatible!)
16. We get tasks by feeding our session URLs
17. + = NSURLSession URL NSURLSessionTask
18. One cookie monster, many cookies.
20. Downloading in Foreground let urlstring = "https://remoteteakettle.com/boiledwater.pdf" let filepath = "Documents/local_teakettle" if let url = NSURL(string: urlstring) { let task = NSURLSession.sharedSession().downloadTaskWithURL(url, completionHandler: { (location:NSURL?, response:NSURLResponse?, error:NSError?) in if let loc = location, path = loc.path { try! NSFileManager.defaultManager().moveItemAtPath(path, toPath:filepath) } }) task.resume() }
21. Downloading in the background
22. Downloading in Foreground let urlstring = "https://remoteteakettle.com/boiledwater.pdf" let filepath = "Documents/local_teakettle" if let url = NSURL(string: urlstring) { let task = NSURLSession.sharedSession().downloadTaskWithURL(url, completionHandler: { (location:NSURL?, response:NSURLResponse?, error:NSError?) in if let loc = location, path = loc.path { try! NSFileManager.defaultManager().moveItemAtPath(path, toPath:filepath) } }) task.resume() }
23. We need a signal.
24. NSURLSessionConfiguration: defines request behaviour and policies
25. Recipe • Create custom session with background configuration
26. Code Create custom session with background configuration:
27. Identifiers must be unique!
28. Life of a background request • Requests start in foreground • App dies • All requests in session finish in background • App starts back up in background
29. UIApplicationDelegate application: handleEventsForBackgroundURLSession : completionHandler: To process the sessions’ requests responses, must recreate session in this method.
30. Recreating Tasks The systems knows which tasks to recreate by the session configuration identifier alone.
31. “The behavior of multiple sessions sharing the same identifier is undefined.”
32. Downloading in Background Does this work?
34. Downloading in Background
35. “Completion handler blocks are not supported in background sessions”
36. Pitfall no completion handlers
37. Downloading in Background
38. Life of a background request • Request starts in foreground • App dies • Request finishes in background • App starts back up in background • App hits NSURLSessionDownloadDelegate methods
39. NSURLSesssionDownloadDelegate URLSession: downloadTask: didFinishDownloadingToURL:
40. Recipe • Create custom session with background configuration • Move code from completion handlers to delegate methods
41. Code Move code from completion handlers to delegate methods
43. Downloading in Background
44. Pitfall No auxiliary request info
45. Documentation?
46. Promising…
47. Nope.
48. Subclass the task?
50. No subclass for you.
51. Recipe • Create custom session with background configuration • Move code from completion handlers to delegate methods • Persist any information needed for request callback
53. Code Persist any information needed for request callback Does this work?
54. YES.
55. let urlstring = "https://remoteteakettle.com/boiledwater.pdf" let filepath = "Documents/local_teakettle" if let url = NSURL(string: urlstring) { let task = NSURLSession.sharedSession().downloadTaskWithURL(url, completionHandler: { (location:NSURL, response:NSURLResponse?, error:NSError?) in if let path = location.path { try! NSFileManager.defaultManager().moveItemAtPath(path, toPath:filepath) } }) task.resume() } Foreground Background 1. background config 2. callback 3. persist request
57. Questions? @purpleyay