Off the Rails: Why It's Time to Move Beyond MVC for Cocoa Development

These are my slides from the May 7, 2014 NSMeetup in San Francisco.

Transcript

1. Off the Rails: Why It’s Time to Move Beyond “MVC” for Cocoa Development ! Adam Block CTO & Co-founder, Breeze www.breezeworks.com
2. Purist
3. > 250 LoC
4. > 500 LoC
5. > 1,000 LoC
6. > 2,000 LoC
7. Model-View-Controller
8. Model-View-Controller
9. Model-View-Controller
10. Model-View-Controller
11. https://www.youtube.com/watch?v=fsaidN93VnA
12. UIViewControllurrghH!!?
14. “A view controller manages a set of views that make up a portion of your app’s user interface.” — Apple, UIViewController Class Reference
15. “A view controller manages a set of views that make up a portion of your app’s user interface.” — Apple, UIViewController Class Reference “View controllers are traditional controller objects in the Model-View- Controller (MVC) design pattern” — Apple, About View Controllers
17. https://speakerdeck.com/trianglecocoa/unburdened-viewcontrollers-by-jay-thrash
18. Concerns
19. Con cerns
20. Con cerns
21. UIViewControllers are view code.* * and routing, which we’ll discuss later.
22. In or Out? • Code directly related to high-level views: IN • Domain logic: OUT • Complex view code: OUT • UI validation: OUT • Formatters: OUT • Data store: OUT
23. the ViewModel
24. What The What? What The What? http://30rocknbc.tumblr.com/post/38332081930/may- everyone-feel-this-way-when-they-open-their
25. Model-View-ViewModel • Implementation of Martin Fowler’s Presentation Model “The essence of a Presentation Model is of a fully self-contained class that represents all the data and behavior of the UI window, but without any of the controls used to render that UI on the screen. A view then simply projects the state of the presentation model onto the glass.”
26. • Exposes all of the fully-composed data to view • Generally, strings and enums • Updates model code in response to commands sent from the view
27. MVVM Example Code
28. Yum! • Very clear which layer you’re working with • Separation of Concerns is easy to enforce • VMs can’t know about VCs! • VCs are much shorter and the routing is clearer • VM code is reusable and decomposable • Testable, finally
29. Ptooey! • Can be overkill for simple screens • VMs themselves can get pretty hairy • VM interface design often ends up being iterative • Bindings • Don’t work with collections or primitives • KVO requirement can be painful • Debugging is declarative and hunting down bugs isn’t always easy
30. the Presenter
31. MVP Example Code
32. Routing • Who owns this? • Controller layer went bye-bye • MVCVM? • Apple makes it hard to have it anywhere but in the UIViewController • Or have the VC query the ViewModel for routing
33. UITableView • Sort of a mess • UITableViewDelegate and UITableViewDataSource mix up View and ViewModel code • Option 1: Selectively forward delegate and data source methods to ViewModel • Option 2: Have the VM be the data source and forward delegate methods as needed
34. UITableView methods: In or Out? - tableView:didSelectRowAtIndexPath: - tableView:viewForHeaderInSection: - numberOfSectionsInTableView: - tableView:cellForRowAtIndexPath: - tableView:numberOfRowsInSection: - tableView:titleForHeaderInSection: - tableView:heightForRowAtIndexPath:
35. UITableView methods: In or Out? - (void)tableView:didSelectRowAtIndexPath: - (UIView *)tableView:viewForHeaderInSection: - (NSInteger)numberOfSectionsInTableView: - (UITableViewCell *)tableView:cellForRowAtIndexPath: - (NSInteger)tableView:numberOfRowsInSection: - (NSString *)tableView:titleForHeaderInSection: - (CGFloat)tableView:heightForRowAtIndexPath:
36. UITableView methods: In or Out? - (void)tableView:didSelectRowAtIndexPath: - (UIView *)tableView:viewForHeaderInSection: - (NSInteger)numberOfSectionsInTableView: - (UITableViewCell *)tableView:cellForRowAtIndexPath: - (NSInteger)tableView:numberOfRowsInSection: - (NSString *)tableView:titleForHeaderInSection: - (CGFloat)tableView:heightForRowAtIndexPath:
37. UITableView Example Code
38. UITableViewCell
39. UITableViewCell “UITableViewCell is Not a Controller” — Brent Simmons
40. UITableViewCell “UITableViewCell is Not a Controller” — Brent Simmons • But maybe just this once?
41. Best Our Practices • Use bindings (MVVM) • Use flag properties if needed • Don’t use UITableViewController (like, ever) • Don’t set ViewModel as UITableView dataSource • Forwards most methods delegate and dataSource methods • UITableViewCells are View + ViewModel • ViewModel owns fetchedResultsController
42. TL;DL(isten) • UIViewControllers aren’t controllers, they’re views • Free your VCs from business logic, formatters, validation, storage, and complex view hierarchies • Use a ViewModel or Presenter to represent the state of your UI abstracted from view code • Bindings simplify links between layers, but aren’t the only way that works • Experiment to figure out what works best for your team
43. References • http://tomdalling.com/blog/software-design/model-view-controller-explained/ • http://joel.inpointform.net/software-development/mvvm-vs-mvp-vs-mvc-the-differences-explained/ • http://www.objc.io/issue-1/lighter-view-controllers.html • https://speakerdeck.com/trianglecocoa/unburdened-viewcontrollers-by-jay-thrash • http://cocoasamurai.blogspot.com/2013/03/basic-mvvm-with-reactivecocoa.html • http://www.sebastianrehnby.com/blog/2013/01/01/skinnier-controllers-using-view-categories • http://inessential.com/2012/12/31/uitableviewcell_is_not_a_controller • http://chris.eidhof.nl/posts/lighter-uiviewcontrollers.html • http://martinfowler.com/eaaDev/PresentationModel.html • http://msdn.microsoft.com/en-us/magazine/dd419663.aspx
44. Projects • Sample Code: https://github.com/ablock/ NSMeetup-MVVM-Talk • https://github.com/ReactiveCocoa/ ReactiveViewModel • https://github.com/jeremytregunna/Binding