Type Safe Assets Handling in Swift

1. Type Safe Resource Handling
in Swift
2015/10/13
potatotips #22

2. About Me
@tasanobu
Kazunobu Tasaka

3. 本日の内容
• リソースを静的型付けし、Type Safeに扱う方法
をお話しします。
• リソースとは
Asset Catalog UIStoryboard
Localizable.strings

4. • リソースのインスタンス生成時
String型の値で指定
Objective-C style
// Assets Catalog
let img = UIImage(named: "Sample")
// Storyboard
let sb = UIStoryboard(name: "Sample", bundle: nil)
.instantiateViewControllerWithIdentifier("Sample")
as? SampleViewController
// Localizable.strings
let str = NSLocalizedString("Sample", comment: “")

5. 問題点
• コンパイラによるチェックが不可
→ 指定方法がStringのため💦
• 実行時にリソースの存在チェック
→ ランタイムエラーが発生するリスクあり
• 戻り値の型 : Optional<T>
→ 使用時にunwrapする必要がある
// 存在しない場合
let sb = UIStoryboard(name: UIApplicationDidBecomeActiveNotification,
bundle: nil)
// Terminating app due to uncaught exception 'NSInvalidArgumentException',
// reason: 'Could not find a storyboard named 'Sample' in bundle NSBundle
let img: UIImage? = UIImage(named: NSURLErrorDomain)
let vc: SampleViewController?
= sb.instantiateViewControllerWithIdentifier("Sample")
as? SampleViewController

6. 改善ポイント
Swift は Type Safe な言語！
• リソースのStringに型情報を持たせる

7. App Specific Enum
extension UIImage {
enum Asset: String {
case Camera = "Camera"
case Home = "Home"
case Mail = "Mail"
}
convenience init!(asset: Asset) {
self.init(named: asset.rawValue)
}
}
Asset ID / Enumの対応付け
• Initializer: Enumでリソースを指定
• Non Optional な戻り値 （リソースの存在が担保されている）

8. Usage
let camera = UIImage(asset: .Camera)
let home = UIImage(asset: .Home)
let mail = UIImage(asset: .Mail)

9. Pros / Cons
• Pros
引数を型付けできる
→ コンパイル時チェックが可能
→ Non-optionalな型が戻り値となる
• Cons
リソースを更新する度にEnum値を更新する必要がある😓

10. • CLツール : リソース用Swiftコードを自動生成
Asset Catalog (UIImage) UIStoryboard
Localizable.strings UIColor
• Homebrewに対応
https://github.com/AliSoftware/SwiftGen
SwiftGen
$
brew
install
swiftgen

11. Usage: UIStoryboard
• コマンドラインを実行
swiftgen-­‐storyboard
/dir/to/storyboards
>
Storyboards.swift

12. // Storyboards.swift
protocol StoryboardScene : RawRepresentable {
static var storyboardName : String { get }
static func storyboard() -> UIStoryboard
static func initialViewController() -> UIViewController
func viewController() -> UIViewController
static func viewController(identifier: Self) -> UIViewController
}
extension StoryboardScene where Self.RawValue == String {
static func storyboard() -> UIStoryboard {
return UIStoryboard(name: self.storyboardName, bundle: nil)
}
static func initialViewController() -> UIViewController {
return storyboard().instantiateInitialViewController()!
}
func viewController() -> UIViewController {
return Self.storyboard().instantiateViewControllerWithIdentifier(self.rawValue)
}
static func viewController(identifier: Self) -> UIViewController {
return identifier.viewController()
}
}
via https://github.com/AliSoftware/SwiftGen

13. // Storyboards.swift
extension UIStoryboard {
struct Scene {
enum Wizard : String, StoryboardScene {
static let storyboardName = "Wizard"
case CreateAccount = "CreateAccount"
static func createAccountViewController() -> CreateAccViewController {
return Wizard.CreateAccount.viewController() as! CreateAccViewController
}
case ValidatePassword = "Validate_Password"
static func validatePasswordViewController() -> UIViewController {
return Wizard.ValidatePassword.viewController()
}
}
enum Message : String, StoryboardScene {
static let storyboardName = "Message"
case Composer = "Composer"
static func composerViewController() -> UIViewController {
return Message.Composer.viewController()
}
case URLChooser = "URLChooser"
static func urlChooserViewController() -> XXPickerViewController {
return Message.URLChooser.viewController() as! XXPickerViewController
}
}
}
struct Segue {
enum Message : String {
case Custom = "Custom"
case Back = "Back"
case NonCustom = "NonCustom"
}
}
}
Storyboard IDに対応
Storyboardファイルに対応
via https://github.com/AliSoftware/SwiftGen

14. Usage
// Initial VC
let initialVC = UIStoryboard.Scene.Wizard.initialViewController()
// Generic ViewController constructor, returns a UIViewController instance
let validateVC = UIStoryboard.Scene.Wizard.ValidatePassword.viewController()
// Dedicated type var that returns the right type of VC (CreateAccViewController here)
let createVC = UIStoryboard.Scene.Wizard.createAccountViewController()
override func prepareForSegue(_ segue: UIStoryboardSegue, sender sender: AnyObject?) {
switch UIStoryboard.Segue.Message(rawValue: segue.identifier)! {
case .Custom:
// Prepare for your custom segue transition
case .Back:
// Prepare for your custom segue transition
case .NonCustom:
// Prepare for your custom segue transition
}
}
via https://github.com/AliSoftware/SwiftGen

15. まとめ
• App Specific Enum を利用すると
静的型付けしてリソースを扱える😄
• SwiftGen: リソース用コードを自動生成可能😄

16. References
• SwiftGen
https://github.com/AliSoftware/SwiftGen
• WWDC’15: Swift in Practice
https://developer.apple.com/videos/wwdc/
2015/?id=411

17. ご静聴ありがとうございました
🙇