A customizable Swift class that triggers a dialog for asking the user to rate the app.

AppRater.swift

//
//  AppRater.swift
//  EasyGraphCalculator_iOS
//
//  Created by arbel03 on 23/03/2016.
//  Copyright © 2016 arbel03. All rights reserved.
//
import UIKit

class AppRater {
    
    static let kFirstDateOpened = "firstDateOpenedKey"
    static let kAmountOpened = "amountOpenedKey"
    static let kShouldDisplay = "shouldDisplayKey"
    static let defaults = NSUserDefaults.standardUserDefaults()
    
    //Insert App Name
    static let appName = ""
    //Insert App ID
    static let appID = ""
    //Choose amount of days before showing the rate dialog
    static let DAYS_BEFORE_SHOWING = 2
    //Show the amount of times the app should open before
    //presenting the dialog
    static let AMOUNT_OPENED_BEFORE_SHOWING = 3
    
    //MARK: - Put this in the viewDidAppear(_:) method of your main view controller
    static func appAppeared(sourceViewController: UIViewController){
        
        //Getting the date when the app was first launched and the current date
        let firstDateOpened = defaults.objectForKey(kFirstDateOpened) as! NSDate
        let currentDate = NSDate()
        //Calculating the amount of days passed since the first launch date
        let daysPassed = NSCalendar.currentCalendar().components(.Day, fromDate: firstDateOpened, toDate: currentDate, options: []).day
        
        //Getting the controller variable for the should display button
        let shouldDisplay = defaults.boolForKey(kShouldDisplay)
        
        //Getting the amount the app has been opened
        let amountOpened = defaults.integerForKey(kAmountOpened)
        
        //Launching the dialog if needed
        if  amountOpened >= AMOUNT_OPENED_BEFORE_SHOWING && daysPassed >= DAYS_BEFORE_SHOWING && shouldDisplay {
            
            let alertView = UIAlertController(title: "Rate \(appName)", message: "If you enjoy \(appName) would you mind taking a moment to rate it? It won't take more than a minute. Thanks for your support!", preferredStyle: .Alert)
            
            alertView.addAction(UIAlertAction(title: "Rate It Now", style: .Default, handler: {
                (action) -> Void in
                let url = NSURL(string: "itms-apps://itunes.apple.com/app/id" + appID)!
                if UIApplication.sharedApplication().canOpenURL(url) {
                    UIApplication.sharedApplication().openURL(url)
                }
            }))
            
            alertView.addAction(UIAlertAction(title: "No, Thanks", style: .Default, handler: {
                (action) -> Void in
                defaults.setBool(false, forKey: kShouldDisplay)
            }))
            
            alertView.addAction(UIAlertAction(title: "Remind Me Later", style: .Cancel, handler: nil))
            
            sourceViewController.presentViewController(alertView, animated: true, completion: nil)
            
            resetCounters()
        }
        
    }
    
    //MARK: Put this in the viewDidLoad(:) method of your main view controller
    static func appLaunched(){
        //Instantiating if needed
        instantiateIfNeeded()
        
        //Then incrementing each time the app is being opened the amount of opened times
        let amountOpened = defaults.integerForKey(kAmountOpened)
        defaults.setInteger(amountOpened+1, forKey: kAmountOpened)
    }
    
    //MARK: -
    static func instantiateIfNeeded() {
        if defaults.valueForKey(kFirstDateOpened) == nil{
            defaults.setValue(NSDate(), forKey: kFirstDateOpened)
        }
        
        if defaults.valueForKey(kAmountOpened) == nil {
            defaults.setInteger(0, forKey: kAmountOpened)
        }
        
        if defaults.valueForKey(kShouldDisplay) == nil {
            defaults.setBool(true, forKey: kShouldDisplay)
        }
    }
    static func resetCounters() {
        //Resetting the first date opened to the current date
        defaults.setObject(NSDate(), forKey: kFirstDateOpened)
        
        //Resetting the amount of opened time
        defaults.setInteger(0, forKey: kAmountOpened)
    }
}