Working with Cocoa and Objective-C

Working with Cocoa / Objective-C

Table of Contents
• Swift Import Process
• Interacting with Objective-C APIs
• Integrating with Interface Builder 
 
and more…

Importing Objective-C
frameworks
• Any Objective-C framework can be imported
directly into Swift 
*like Foundation, UIKit and common C Libraries
!
import Foundation
import UIKit

Import Process
• Objective-C header ﬁles are compiled to
modules, which are imported as Swift APIs
• Type Remapping:
• id → AnyObject
• NSString → String …

Interacting with Objective-C
APIs

Initializers
• No alloc in Swift!
!
// Objective-C
UITableView *myTableView = [[UITableView alloc]
initWithFrame:CGRectZero style:UITableViewStyleGrouped];
!
// Swift
let myTableView = UITableView(frame: CGRectZero, style: .Grouped)

Factory Methods
• Objective-C factory methods get mapped to
convenience initialisers in Swift
!
// Objective-C
UIColor *color = [UIColor colorWithRed:0.5 green:0.0
blue:0.5 alpha:1.0];
!
// Swift
let color = UIColor(red: 0.5, green: 0.0, blue: 0.5,
alpha: 1.0)

Accessing Properties
• Use dot syntax
!
let str: NSString = "hoge"
// get
let count = str.length
!
let label = UILabel()
// set
label.text = str

Methods
• Use dot syntax
!
// Objective-C
[myTableView insertSubview:mySubview atIndex:2];
!
!
// Swift
myTableView.insertSubview(mySubview, atIndex: 2)
• () are needed  
even when a method doesn’t have any arguments
!
myTableView.layoutIfNeeded()

AnyObject
• AnyObject is id in Swift.
• Swift imports id as AnyObject
!
// Any class type can be assigned.
var myObj: AnyObject = UITableView()
!
// a different type object can be assigned.
myObj = UIView()

Unsafe Code
• The speciﬁc type of AnyObject isn’t known  
until runtime…
!
var myObj: AnyObject = UITableView()
!
// Crash
// because UITableView cannot respond to "length()"
myObj.length()

Optionals!
• The following method calls behave like implicitly
unwrapped optionals when calling an Objective-
C method.
!
var myObj: AnyObject = NSDate()
!
// These method are never executed.
let count = myObj.count?
let myChar = myObj.characterAtIndex?(5)
!
if let frame = myObj.frame {
println("frame: (frame)")
}

Downcasting
• Casting from AnyObject to a more speciﬁc
object type returns an optional value.
!
let userDefaults = NSUserDefaults.standardUserDefaults()
let lastDate: AnyObject? =
userDefaults.objectForKey("LastDate")
!
// This downcasting is not guaranteed to succeed.
if let date = lastDate as? NSDate {
println("(date.timeIntervalSinceReferenceDate)")
}
!
// if 100% sure to succeed, “as” can be used!
let date = lastDate as NSDate
let timeInterval = date.timeIntervalSinceReferenceDate

Working with nil
• When importing Objective-C APIs,  
all classes in arguments and return types are converted to
implicitly unwrapped optional!
• Should check and unwrap an implicitly unwrapped optional object 
var view: UIView! = UIView()
view = nil
!
// crash!
//println("(view.frame)")
!
// SHOULD check whether view is nil or not
if view != nil {
println("(view.frame)")
} else {
println("view is nil...")
}

Blocks
• “Swift Closures” and “Objective-C Blocks” are
compatible
• Objective-C blocks are converted to Swift Closures
!
// Objective-C
void (^completionBlock)(NSData *, NSError *) =
^(NSData *data, NSError *error) {/* ... */}
!
// Swift
let completionBlock: (NSData, NSError) -> Void =
{data, error in /* ... */}

Capture Semantics
• Basically, Closures have similar semantics as
Blocks
• Difference:
• Variables are mutable rather than copied
• __block in Objective-C is default behavior

@objc attribute
• When a Swift class inherits from NSObject, the class automatically
compatibele with Objective-C.
• @objc attribute is needed to use from Objective-C if a Swift class
doesn't inherit from NSObject.
• @objc attribute makes Swift APIs available in Objective-C
@objc(SomeClass)
class SomeClass {
var value: Int
init(value: Int) {
self.value = value
}
func printValue() {
println("value is (value)")
}
}

Swift APIs in Objective-C
!
// Swift
init(songName: String, artist: String)
!
// Objective-C
- (instancetype)initWithSongName:(NSString *)songName
artist:(NSString *)artist;
!
!
// Swift
func playSong(name: String)
!
// Objective-C
- (void)playSong:(NSString *)name;

Selector in Swift
• A Objective-C selector is a type that refers to an
Objective-C method
• Objective-C selectors are represented by
Selector structure in Swift
!
let mySelector: Selector = "tappedButton:"

Common Use Case
!
class MyViewController: UIViewController {
let myButton = UIButton(frame:CGRect(x:0,y:0,width:50,height: 50))
override init(nibName nibNameOrNil: String?, bundle
nibBundleOrNil: NSBundle?) {
super.init(nibName: nibNameOrNil, bundle: nibBundleOrNil)
myButton.addTarget(self, action: "tappedButton:",
forControlEvents: .TouchUpInside)
}
!
required init(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
func tappedButton(sender: UIButton!) {
println("tapped button")
}
}

Integrating with  
Interface Builder

Outlets and Actions
• @IBOutlet for Outlets, @IBAction for Actions
• The type of the outlet should be implicitly unwrapped
optional.
!
class MyViewController: UIViewController {
@IBOutlet weak var button: UIButton!
@IBAction func buttonTapped(AnyObject) {
println("button tapped!")
}
}

Strong and Weak
• Swift properties are strong by default
• weak keyword indicates that a property has a
weak reference to the object
• This keyword can be used only for optional
properties.

Read/Write and Read-Only
• Swift has no readwrite and readonly attributes
• let for readonly
• var for readwrite

Copy Semantics
• @NSCopying is copy property in Objective-C
• must conform to NSCopying protocol

Wrap Up
• Looking through how to work with Cocoa /
Objective-C
• For more detail, 
 
Using Swift with Cocoa and Objective-C 
https://developer.apple.com/library/ios/
documentation/Swift/Conceptual/
BuildingCocoaApps/

Working with Cocoa and Objective-C

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