Swift and Objective-C: Best Friends Forever?

See how you can work with both languages in the same project, what works well and what the pitfalls are.

Most recently given at CocoaConf Atlanta, December 2014.

Original version presented October 14, 2014 at the Swift Language Users Group in San Francisco, CA.

Transcript

1. Swift and Objective-C:
 Best Friends Forever? Jonathan Blocksom Capital One @jblocksom blocksom@gmail.com
2. Jonathan Blocksom • iOS Developer at Capital One
 Former instructor at Big Nerd Ranch • @jblocksom • jonathan.blocksom@capitalone.com
 blocksom@gmail.com We’re hiring!
3. Agenda • Swift - Obj-C Bridge Basics • Adding Swift to Objective-C • More Details • Adding Objective-C to Swift • Calling C from Swift
4. Why? • There is a handy Swift library you want to use in Obj-C • There is a handy Obj-C library you want to use in Swift • You have a big Obj-C codebase and you want to learn Swift • You’ve been using Swift elsewhere and you like it better • It’s shiny and that affects your rationality
5. Swift at Capital One • Native rewrite of mid sized iPhone App • Due in 2015, targeting iOS 7 and 8 • Skilled team that likes the bleeding edge • July 2, 2014:
 ~180 .m files in project
 October 9, 2014:
 190 .m files
 103 .swift files
 (including tests) 0 50 100 150 200 250 300 Commits over time Objective-C and Swift Class Count
6. Overview: Swift Compatability • Swift built for Objective-C Compatibility • Also works with C • Will not accept C++’s friend request Swift C Obj-C C++
7. Objective-C and Swift Type Bridging Objective-C Swift BOOL Bool NSInteger Int NSString * String SEL Selector id AnyObject NSArray * [AnyObject]! NSDictionary * [NSObject: AnyObject] ^{} {} Class AnyClass
8. ? and ! • Objective-C: Pointers to objects can be nil • Swift: No nil objects • ? • Declaring parameter to be optional (may be nil) • Testing for nil • ! • Implicitly unwrapped optionals (won’t be nil)
9. Subclassing NSObject MyNSObject SwiftNSObj AnotherSwiftObj Swift Obj-C
10. Swift Features Not Available to Obj-C • Generics • Tuples • Swift Enums • Swift Structs • Top-level Swift functions • Global variables defined in Swift • Typealiases defined in Swift • Swift-style variadics • Nested types • Curried functions
11. Trying it Out:
 Adding Swift to Existing Obj-C • Simple Project • Add some Swift to do something interesting
12. Xcode: Swift - ObjC Headers Swift Obj-C Product- Bridging- Header.h Product- Swift.h You fill this file in Xcode Makes this
13. Adding Swift to Existing Obj-C Project • Add a Swift file • In Obj-C file: • #import “ProductName-Swift.h” • Use classes, functions as usual • Make sure target is 7.0 or above
14. Using Swift Objects • Class methods: just call them • Instantiating: use class method or inherit from NSObject • Instance Methods: just call them
15. Swift • Function must be in a class • No @objc keyword because of NSObject #import "DemoApp-Swift.h" - (void)viewDidLoad { [super viewDidLoad]; Foo *aFoo = [[Foo alloc] init]; [aFoo bar]; } import Foundation public class Foo : NSObject { public func bar() { println("Hi from Swift") } } • Include <ProductName>-Swift.h • Create object and send message as usual
16. Bridging Classes in Action
17. Bringing Swift to Obj-C • Simple Swift class • Subclasses NSObject • Name: String
 Weight: Int
 Type: Swift Enum public class CuriousWidget: NSObject { enum WidgetType { case FlobGangle case HuffTanker case GorbNorgle } var name: String var weight: Int var type = WidgetType.FlobGangle override init() { name = "Widget" weight = 1 } }
18. Bringing Swift to Obj-C • Basic Usage • Allocate, initialize
 Set name
 Set weight • Cannot set type: self.widget = [[CuriousWidget alloc] init]; self.widget.name = @"thingybob"; NSLog(@"%@", self.widget); self.widget.weight = 2; NSLog(@"%ld", self.widget.weight);
19. Checking Obj-C Generated Header • Opt-click on
 #import “BFFDemo-Swift.h" • Select Preprocess from corner squares drop thingy
20. Bringing Swift to Obj-C • Obj-C Class Definition: __attribute__((objc_runtime_name("_TtC7BFFDemo13CuriousWidget"))) __attribute__((objc_subclassing_restricted)) @interface CuriousWidget : NSObject @property (nonatomic, copy) NSString * name; @property (nonatomic) NSInteger weight; - (instancetype)init __attribute__((objc_designated_initializer)); @end Missing type enum property Can’t subclass * Actual Class name: BFFDemo.CuriousWidget
 (Check via NSStringFromClass or class_getName) More on name mangling:
 https://mikeash.com/pyblog/friday-qa-2014-08-15-swift-name-mangling.html
21. Subclassing Swift @objc Classes • You can’t • You can add category methods @interface CuriousWidget(DupeWithName) - (CuriousWidget *)dupeWithName:(NSString *)newName; @end @implementation CuriousWidget(DupeWithName) - (CuriousWidget *)dupeWithName:(NSString *)newName { CuriousWidget *newWidget = [[CuriousWidget alloc] init]; newWidget.name = newName; newWidget.weight = self.weight; return newWidget; } @end (see the bug?)
22. KVO • Can observe property changes in @objc properties [self.widget addObserver:self forKeyPath:@"name" options:NSKeyValueObservingOptionNew context:nil]; - (void)observeValueForKeyPath:(NSString *)keyPath ofObject:(id)object change:(NSDictionary *)change context:(void *)context { NSLog(@"Observed change, widget is %@“, self.widget); }
23. Method Swizzling • You know you want to
24. Method Swizzling • Must use dynamic dispatch
 (Implicit with @objc) • Standard Obj-C swizzle w/ method_exchangeImplementatio n @objc public func incWeight() { weight += 1 } @objc public func decWeight() { weight -= 1 } NSLog(@"Weight: %ld", (long)self.widget.weight); [self.widget incWeight]; NSLog(@"Weight: %ld", (long)self.widget.weight); SwizzleMethod([self.widget class], @selector(incWeight), @selector(decWeight)); NSLog(@"Weight: %ld", (long)self.widget.weight); [self.widget incWeight]; NSLog(@"Weight: %ld", (long)self.widget.weight); 2014-10-18 10:36:38.287 BFFDemo[57175:2386745] Weight: 1 2014-10-18 10:36:38.288 BFFDemo[57175:2386745] Weight: 2 2014-10-18 10:36:38.288 BFFDemo[57175:2386745] Swizzled 2014-10-18 10:36:38.288 BFFDemo[57175:2386745] Weight: 2 2014-10-18 10:36:38.288 BFFDemo[57175:2386745] Weight: 1 Swift Functions in class: Output:
25. Dynamic Dispatch • Using Obj-C Runtime to look up method implementation • Not default when using Swift classes • @objc enables by default
26. Calling Objective-C from Swift
27. Naming Rules • First parameter name is implicit
 - (void)initWithFoo:(MyFoo *)foo
 withFoo is dropped, becomes
 override public func init(foo: MyFoo)
29. Product-Bridging-Header.h • #import all your Obj-C stuff that you want in Swift • One per project • Example: NSObject MyNSObject SwiftNSObj AnotherSwiftObj MyViewController creates #import "ViewController.h" #import "MyNSObject.h"
30. Beware Circular Dependencies • Don’t include Product-Swift.h in Obj-C .h files MyObject MyVC Bridge Header SwiftVC Use forward declaration (@class)
31. Optionals and Implicitly Unwrapped Optionals • Must know your ?s and !s • Many Cocoa APIs have been vetted • By default any NSObject return value should be ? var bar:SomeClass? if let aBar = bar { aBar.doSomething() }
32. bridgeToObjectiveC() • Removed in Beta 5 • Do you remember beta 5? • Now implicitly bridged
 var str = "Hello, playground" str.bridgeToObjectiveC().length
33. Testing Classes in Swift • use is instead of isMemberOfClass • use as? instead of isKindOfClass
34. Swift and C • Search “Mike Ash NSSpain Swift and C” • Demonstrates using C with Swift • Pointers!
35. Bridged C Pointers
36. Alamofire in Obj-C Case Study
37. Scenario • You are a grumpy old graybeard and the young hotshot has included AlamoFire for networking in your project • Your tech lead has forbidden NSURLConnection • You haven’t bothered to figure out NSURLSession • CocoaPods broke so you can’t include AFNetworking • You’re pretty sure running curl in the background won’t make it through app review
38. AlamoFire • Swift networking • How to use from Obj-C? Response Handling Alamofire.request(.GET, "http://httpbin.org/get", parameters: ["foo": "bar"]) .response { (request, response, data, error) in println(request) println(response) println(error) }
39. Types Alamofire.request(…).response{…} public func request(
 method: Method, 
 URLString: URLStringConvertible, 
 parameters: [String: AnyObject]? = nil, 
 encoding: ParameterEncoding = .URL) 
 -> Request public class Request public func response( completionHandler: (…) -> Void) -> Self Method chain to create request object
40. Creating the response instance • Hey look, a sharedInstance! public func request(…) -> Request { return request(encoding.encode(URLRequest(method, URLString), parameters: parameters).0) } /** Creates a request using the shared manager instance for the specified URL request. If `startRequestsImmediately` is `true`, the request will have `resume()` called before being returned. :param: URLRequest The URL request :returns: The created request. */ public func request(URLRequest: URLRequestConvertible) -> Request { return Manager.sharedInstance.request(URLRequest.URLRequest) }
41. Manager sharedInstance • Use the singleton! Add @objc: • Call in ViewController.m: • Good, as can’t call alloc because it’s not an NSObject public class Manager { /** A shared instance of `Manager`, used by top-level Alamofire request methods, and suitable for use directly for any ad hoc requests. */ public class var sharedInstance: Manager { Manager *manager = [Manager sharedInstance]; @objc public class Manager {
42. URLRequest • Two request calls • URLRequestConvertible: public func request(
 method: Method, 
 URLString: URLStringConvertible, 
 parameters: [String: AnyObject]? = nil, 
 encoding: ParameterEncoding = .URL) 
 -> Request public func request( URLRequest: URLRequestConvertible) -> Request /** Types adopting the `URLRequestConvertible` protocol can be used to construct URL requests. */ public protocol URLRequestConvertible { /// The URL request. var URLRequest: NSURLRequest { get } } extension NSURLRequest: URLRequestConvertible { public var URLRequest: NSURLRequest { return self } }
43. Request method • Takes URLRequestable • Protocol declared by Alamofire • Alamofire extends NSURLRequest to conform to this… • …but compiler doesn’t really agree
44. Wrap request method • Obj-C version of request method • Call from Obj-C: • Had to add @objc to Request class in Swift @objc public func requestFromObjC(req: NSURLRequest) -> Request { return request(req) } Manager *manager = [Manager sharedInstance]; NSURL *url = [NSURL URLWithString:@"http://httpbin.org/get"]; NSURLRequest *req = [NSURLRequest requestWithURL:url]; Request *r = [manager requestFromObjC:req];
45. Response method • Sets response handler • Add @objc to response function and now we can call: • Not very idiomatic… [r response:^(NSURLRequest *r2, NSHTTPURLResponse *resp, id foo, NSError *err) { NSLog(@"Request: %@", r2); NSLog(@"Response: %@", resp); }];
46. Better response method • @objc (setResponse:) … • Looks better on Obj-C side • Can even use property assignment! [r setResponse:… ]; r.response = ^(NSURLRequest *r2, NSHTTPURLResponse *resp, id foo, NSError *err) { NSLog(@"Request: %@", r2); NSLog(@"Response: %@", resp); };
47. Final Result • Steps we took:
 Sprinkled @objc here and there
 Wrapped a function
 Set some Obj-C style method names Manager *manager = [Manager sharedInstance]; NSURL *url = [NSURL URLWithString:@"http://httpbin.org/get"]; NSURLRequest *req = [NSURLRequest requestWithURL:url]; Request *r = [manager requestFromObjC:req]; r.response = ^(NSURLRequest *r2, NSHTTPURLResponse *resp, id foo, NSError *err) { NSLog(@"Request: %@", r2); NSLog(@"Response: %@", resp); }; Swift Version
 Alamofire.request(.GET, "http://httpbin.org/get", parameters: ["foo": "bar"]) .response { (request, response, data, error) in println(request) println(response) }
48. Should you do this? • Probably not • But it’s fun to push the boundaries
49. Gotchas & Lessons Learned • ProductName-Swift.h header
 Name mangling hard if ProductName has been changed • Wrong Import: don’t import Swift class, import -Swift.h • Optionals that aren’t • Regen Certificates • Go slow — integrate a bit at a time, especially on a big team
50. Wrong import • Accidentally importing MyClass.swift instead of App-Swift.h: • Caused by this in SomeObjC.m: #import "Blah.swift" // Should have been #import "<Product>-Swift.h"
51. <ProductName>-Swift.h Header • Must include to access Swift objects • May be name mangled: non alphanumeric chars become underscores • ProductName different for different targets • Use Product Module name build setting • Our experience: • Spurious compiler errors after successful build • Lots of clean & rebuild required
52. Optionals (and things that should be optionals) • Easy to get properties that could be nil which don’t look that way in Swift • If they are nil at runtime your app crashes • Double check using if let constructs
53. Example • currentLocation was nil, app crashed • Shouldn’t Swift type checker have noticed? • @property (copy, nonatomic) CLLocation currentLocation;

54. Enabling Swift & New Signing Certificate • Need to enable “Embedded Content Contains Swift” build setting • Certificates made before Xcode 6 beta can’t include Swift for iOS 8 • Needed to regenerate certificate • Worked on iOS 7, only shows up in release builds…
55. Other Gotchas • initWithCoder implementations • Int vs Integer • Lots of CGFloat casting • Module names are case sensitive
 (it’s not AlamoFire)
56. WWDC Sessions on Swift & Obj-C • 406: Integrating Swift with Obj-C • 407: Swift Interoperability in Depth Watch this one!
57. My Favorite Swift Resources in No Particular Order • Mike Ash NSBlog • Erica Sadun Blog
 http://ericasadun.com/ • Daniel Steinberg Swift Book • objc.io Swift Issue • Apple iBooks on Swift
 (Be sure to update from iBooks; may need to delete and redownload)
58. Questions & Thank You • Jonathan Blocksom
 jonathan.blocksom@capitalone.com
 @jblocksom We’re hiring!