cocoa_swift_style_guide.md

Official SlideShare Cocoa/Swift Style Guide

This is the SlideShare Cocoa/Swift Style Guide we are using for our iOS 8 only app written in Swift. Please feel free to submit pull requests, so that this may be helpful for anyone else using Swift. This document lays out our conventions for using Swift with the Cocoa APIs for iOS.

You can download the app at http://lnkd.in/ssios

Table Of Contents

• Protocols
• UITableView/UICollectionView
• Strings
• NSNotification
• App Delegate
• Core Foundation
• View Controllers
• UIView
• Objective-C Interoperability

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Protocols

• The ReusableView Protocol should be used by any view used by a UICollectionView or UITableView that needs a reuse identifier. You will see how this is used in the UITableView section.

protocol ReusableView {
    static var ReuseIdentifier: String { get }
    static var NibName: String { get }
}

UITableView & UICollectionView

• In a UITableViewCell/UICollectionViewCell subclass, create a read-only computed property for the reuse identifier for the cell. Use camel case with first letter uppercase, because it is a constant. Note: Please use the protocol listed in the conformance.

class TableViewCell: UITableViewCell, ReusableView {
    static let ReuseIdentifier: String = "TableViewCellIdentifier"
    static let NibName: String = "CustomTableViewCell"
}

Reasoning: When registering cells for reuse in a UITableView or UICollectionView, you need the nib name to load the nib and the reuse identifier.

Strings

• Put any user-facing string in the Localizable.strings file with a key in snake case. Use NSLocalizedString when accessing the strings in code.

// Localizable.strings //
// <App Section>
"user_facing_string_key" = "This is a user-facing string."

// Someting.swift //
var userFacing = NSLocalizedString("user_facing_string_key", comment: "")

NSNotification

• Name notifications in reverse domain format with the notification name in snake case.

com.linkedin.slideshare.notification_name

• Create a struct to hold all notification names as constants.

struct GlobalNotifications {
    static let ABC = ""
}

• Create notification handlers as lazy closures.

private lazy var handleNotification: (NSNotification!) -> Void { [weak self] notification in
    // Handle the notification
}

Reasoning: This way you can define capture semantics for self and also use the identifier as the selector in the addObserver method (see below) instead of a string. This gives you the safety of the compiler.

• Create a registerNotifications() method and deregisterNotifications().

func registerNotifications() {
    let notificationCenter = NSNotificationCenter.defaultCenter()

    notificationCenter.addObserver(self, selector: handleNotificationABC, name: GlobalNotifications.ABC, object: nil)
}

func deregisterNotifications() {
    NSNotificationCenter.defaultCenter().removeObserver(self)
}

App Delegate

• Abstract initialization of the application into a separate class.

class AppInitializer {
    func onAppStart() {
        // content
    }
}

Core Foundation

• When using Core Graphics structs, such as CGRect, use the initializers instead of the older CGRectMake method.

var rect = CGRect(x: 10, y: 10, width: 45, height: 300)

• If you need to make an instance of a struct zeroed out, utilize the class constant.

var zeroRect = CGRect.zeroRect

View Controllers

• If the view controller is associated with a Storyboard, create a class method named createInstance to return an initialized instance of the view controller from the Storyboard.

static func createInstance() -> MasterViewController {
    return UIStoryboard.initialControllerFromStoryboard("Master") as! MasterViewController
}

Reasoning: Use static if you are not going to make a subclass of this class. If you are going to make a subclass, change it to class func.

• If you have the situation described above, but have properties that need to be initialized, also create helper methods following the designated/convenience initializer type pattern like so.

static func createInstanceWithId(id: Int) -> MasterViewController {
        let masterViewController = createInstance()
        masterViewController.id = id
        return masterViewController
}

UIView

• If you have a class that inherits from UIView and has a XIB file where it is layed out, create a class method named createInstance similar to the example in the View Controllers section.

class CustomView: UIView {

    private static let NibName: String = "CustomView"

    static func createInstance() -> CustomView {
        return NSBundle.mainBundle().loadNibNamed(nibName, owner: nil, options: nil)[0] as! CustomView
    }
}

Objective-C Interoperability

• You must have a single Objective-C bridging header for Object-C interoperability. However, if a certain set of code you are importing has multiple header files; group them into another header file.

// <Product-Name>-Bridging-Header.h
#import "SDWebImageHeader.h"

// SDWebImageHeader.h
#import <SDWebImage/UIImageView+WebCache.h>
#import <SDWebImage/UIImage+MultiFormat.h>
#import <SDWebImage/SDWebImagePrefetcher.h>