Gwendolyn Weston "While Your App Was Sleeping"

Transcript

1. 1.

   While Your App Was Sleeping Gwendolyn Weston
 @purpleyay

2. 2.

   Background Transfer Services keeps requests going even if the app

   is terminated by the system
3. 3.

   Motivation

4. 4.

   A Teakettle • That requires you to stand near it

   • And watch it in order for it to boil water
5. 5.

   Where can this happen in our apps?

6. 6.

   PlanGrid

7. 7.

   To guarantee download completion • Change device settings so it

   never locks • Stay on the app
8. 8.

   Downloading without Background Transfer Services is like watching water boil.

9. 9.

   Overview • How to download in the foreground • How

   to make that request background compatible • How to navigate common pitfalls
10. 10.

    Downloading in the foreground

11. 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. 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. 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. 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. 15.

    NSURLSessionTask • NSURLSessionDownloadTask • NSURLSessionUploadTask • NSURLSessionDataTask - short-lived requests

    (not background compatible!)
16. 16.

    We get tasks by feeding our session URLs

17. 17.

    + = NSURLSession URL NSURLSessionTask

18. 18.

    One cookie monster, many cookies.

19. 19.

    None
20. 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. 21.

    Downloading in the background

22. 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. 23.

    We need a signal.

24. 24.

    NSURLSessionConfiguration: defines request behaviour and policies

25. 25.

    Recipe • Create custom session with background configuration

26. 26.

    Code Create custom session with background configuration:

27. 27.

    Identifiers must be unique!

28. 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. 29.

    UIApplicationDelegate application: handleEventsForBackgroundURLSession : completionHandler: To process the sessions’ requests

    responses, must recreate session in this method.
30. 30.

    Recreating Tasks The systems knows which tasks to recreate by

    the session configuration identifier alone.
31. 31.

    “The behavior of multiple sessions sharing the same identifier is

    undefined.”
32. 32.

    Downloading in Background Does this work?

33. 33.

    None
34. 34.

    Downloading in Background

35. 35.

    “Completion handler blocks are not supported in background sessions”

36. 36.

    Pitfall no completion handlers

37. 37.

    Downloading in Background

38. 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. 39.

    NSURLSesssionDownloadDelegate URLSession: downloadTask: didFinishDownloadingToURL:

40. 40.

    Recipe • Create custom session with background configuration • Move

    code from completion handlers to delegate methods
41. 41.

    Code Move code from completion handlers to delegate methods

42. 42.

    None
43. 43.

    Downloading in Background

44. 44.

    Pitfall No auxiliary request info

45. 45.

    Documentation?

46. 46.

    Promising…

47. 47.

    Nope.

48. 48.

    Subclass the task?

49. 49.

    None
50. 50.

    No subclass for you.

51. 51.

    Recipe • Create custom session with background configuration • Move

    code from completion handlers to delegate methods • Persist any information needed for request callback
52. 52.

    None
53. 53.

    Code Persist any information needed for request callback Does this

    work?
54. 54.

    YES.

55. 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
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    None
57. 57.

    Questions? @purpleyay