Swift in Practice

Take advantage of new APIs while deploying to older OS releases

Problem: Users on different OS releases

Solution: Adopt new features and support the older OS releases

• Always use the Latest SDK to access complete set of APIs

• Use Deployment Target to set an application’s minimum supported OS release

• Manually check Framework, Class, etc.

  • Framework: manually check framework as optional

  • Class: manually check if a method/function available.

• Compile-Time API Availability Checking.

Enforce expected application behavior using enums and protocols

Use Case: Asset Catalog Identifiers

extension UIImage {
    enum AssetIdentifier: String {
        case isabella = "Isabella"
        case william = "William"
        case Olivia = "Olivia"
    }
    
    convenience init!(assertIdentifier: AssetIdentifier) {
        self.init(named: assertIdentifier.rawValue)
    }
}

• Centrally located constants

• Doesn’t pollute global namespace

• Must use one of the enum cases

• Image initialization are not failable

Use Case: Segue Identifiers

class ViewController: UIViewController {
    enum SegueIdentifier: String {
        case ShowImportUnicorn = "ShowImportUnicorn"
        case ShowCreateNewUnicore = "Show CreateNewUnicorn"
    }
    
    override func prepareForSegue(segue: UIStoryboardSegue, sender: AnyObject?) {
        guard let identifier = segue.identifier, segueIdentifier = SegueIdentifier(rawValue: identifier)
        else { fatalError("Invalid segue identifier \(segue.identifier).")}
        
        switch segueIdentifier {
            case .ShowImportUnicorn:    // Config...
            case .ShowCreateUnicor:     // Config...
        }
    }
}

When new case added to enum, then the compiler will tell us switch is not exhausted.

class ViewController: UIViewController {
    func performSegueWithIdentifier(segueIdentifier: SegueIdentifier, sender: AnyObject?) {
        performSegueWithIdentifier(segueIdentifier.rawValue, sender: sender)
    }
}

To avoid duplicate all of the smart solution showed above, use Protocol

protocol SegueHandlerType {
    typealias SegueIdentifier: RawRepresentable
}

// Shared Implementation.
extension SegueHandlerType where Self: UIViewController, SegueIdentifier.RawValue == String {
    func segueIdentifier(for segue: UIStoryboardSegue) -> SegueIdentifier {
        guard let identifier = segue.identifier,
            let segueIdentifier = SegueIdentifier(rawValue: identifier)
        else { fatalError("Unknown segue: \(segue))") }
        return segueIdentifier
    }
    
    func performSegueWithIdentifier(segueIdentifier: SegueIdentifier, sender: AnyObject?) {
        performSegueWithIdentifier(segueIdentifier.rawValue, sender: sender)
    }
}

class ViewController: UIViewController, SegueHandlerType {
    enum SegueIdentifier: String {
    // ...
    }
}