One of the first things every iOS developer should add to their project is a way to detect what is happening at launch. It doesn’t have to be complicated, but trust me, this can potentially save you some trouble later on.
I usually create a BaseAppDelegate class that will be responsible for detecting the following:
- is it the first time the user launch the app?
- how many times did the user launch count?
- is this launch the first launch after an app upgrade?
- when was last time the user launched the app before this launch?
Here is the code I usually put in this BaseAppDelegate class:
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| // | |
| // BaseAppDelegate.swift | |
| // | |
| // Created by Cyril Chandelier on 21/04/2018. | |
| // Copyright © 2018 Cyril Chandelier. All rights reserved. | |
| // | |
| import UIKit | |
| class BaseAppDelegate: UIResponder, UIApplicationDelegate { | |
| // MARK: – Dependencies | |
| lazy var bundle: Bundle = Bundle.main | |
| lazy var userDefaults: UserDefaults = UserDefaults.standard | |
| // MARK: – UIApplicationDelegate methods | |
| @discardableResult func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplicationLaunchOptionsKey : Any]? = nil) -> Bool { | |
| print("Initializing app") | |
| // Try to detect first launch | |
| if launchCount == 0 { | |
| print("…first launch detected") | |
| applicationFirstLaunch() | |
| } | |
| // Update app launches count | |
| launchCount += 1 | |
| print("…\(launchCount) launches") | |
| // Try to detect version upgrade | |
| let currentVersion = bundle.object(forInfoDictionaryKey: "CFBundleShortVersionString") | |
| as! String | |
| if let lastLaunchVersion = lastLaunchVersion, currentVersion != lastLaunchVersion { | |
| print("…upgrade detected") | |
| applicationDidUpgrade(from: lastLaunchVersion, to: currentVersion) | |
| } | |
| // Update last known version if new | |
| if lastLaunchVersion != currentVersion { | |
| print("…saving new version: \(currentVersion)") | |
| lastLaunchVersion = currentVersion | |
| } | |
| // Update last known launch date | |
| print("…saving current launch date") | |
| appLastLaunchDate = Date() | |
| // Make sure user defaults are saved | |
| userDefaults.synchronize() | |
| return true | |
| } | |
| // MARK: – Optional methods to override | |
| func applicationFirstLaunch() {} | |
| func applicationDidUpgrade(from: String, to: String) {} | |
| // MARK: – Utilities | |
| private(set) var launchCount: Int { | |
| get { | |
| return userDefaults.integer(forKey: Keys.appLaunchCount) | |
| } | |
| set { | |
| userDefaults.set(newValue, forKey: Keys.appLaunchCount) | |
| } | |
| } | |
| private(set) var lastLaunchVersion: String? { | |
| get { | |
| return userDefaults.string(forKey: Keys.appLastLaunchVersion) | |
| } | |
| set { | |
| if let newValue = newValue { | |
| userDefaults.set(newValue, forKey: Keys.appLastLaunchVersion) | |
| } else { | |
| userDefaults.removeObject(forKey: Keys.appLastLaunchVersion) | |
| } | |
| } | |
| } | |
| private(set) var appLastLaunchDate: Date? { | |
| get { | |
| return userDefaults.object(forKey: Keys.appLastLaunchDate) as? Date | |
| } | |
| set { | |
| if let newValue = newValue { | |
| userDefaults.set(newValue, forKey: Keys.appLastLaunchDate) | |
| } else { | |
| userDefaults.removeObject(forKey: Keys.appLastLaunchDate) | |
| } | |
| } | |
| } | |
| // MARK: – User default keys | |
| private struct Keys { | |
| static let appLaunchCount = "appLaunchCount" | |
| static let appLastLaunchVersion = "appLastLaunchVersion" | |
| static let appLastLaunchDate = "appLastLaunchDate" | |
| } | |
| } |
You just need to make your AppDelegate extends BaseAppDelegate, and call the super method in application(_:didFinishLaunchingWithOptions). Then, you can choose (or not) to override (and therefore implement something for) the applicationFirstLaunch() and/or applicationDidUpgrade(from:to:) methods.
Here are a couple use cases where having this super-class reveals itself handy:
- I want to know how many times a users came into the app for my analytics
- I want to know when a users re-open the app after a while, to customize his experience as a returning user
- I want to show a “What’s new” popup to my returning users who upgraded their app
- my app was a paid app before, and now it’s free with In-App Purchases to unlock some content, but I don’t want my users who already paid to hit my paywall