Difference between mutable array and immutable array?

Ans : 

Mutable Array content can be changed but Immutable Array content can not be changed.

You can insert, update, remove item from Mutable Array, but same is not possible in Immutable Array. There is no any methods like RemoveItem or ReplaceItem for Immutable Array, which are available for Mutable Array.

So in Immutable Array, content can not be changed after initialisation. It is either be initialised by content or by nil.

Use of Immutable array 

1. Used when we want to give array to other coder who can't be change array content.
2. Used when only fixed contents are there like array of months, days which can't be changed.

Write program for ascending sorting Int Array in any language

Ans : 
(Interviewer told syntax doesn't matter, write pseudo-code type program)

1. Not using direct function.

 void main()
    {

        int i, j, a, n, number[30];
        printf("Enter the value of N \n");
        scanf("%d", &n);

        printf("Enter the numbers \n");
        for (i = 0; i < n; ++i)
            scanf("%d", &number[i]);

        for (i = 0; i < n; ++i)
        {

            for (j = i + 1; j < n; ++j)
            {

                if (number[i] > number[j])
                {

                    a =  number[i];
                    number[i] = number[j];
                    number[j] = a;

                }

            }

        }

        printf("The numbers arranged in ascending order are given below \n");
        for (i = 0; i < n; ++i)
            printf("%d\n", number[i]);

    }

2. If we write in swift using higher order function, then

var numbers = [45,6,113,56,8,56,43,78]

print(numbers.sort()) //Sorting in Ascending order

print(numbers.sort(>)) //Sorting in Descending order

Interviewer mostly asked this question to check your programming logic. So he/she don't require syntax.

Q. Sorting strings array
A.
Method 1 : 
var sortedArray = swiftArray.sorted { $0.localizedCaseInsensitiveCompare($1) == ComparisonResult.orderedAscending }

Method 2 : 
let sortedNames = names.sort { $0.name < $1.name }
let sortedNames = names.sorted(by: <)

What types of feature google map provide to developers?

Ans : 

Google map features :

• Plotting places Near Me. Like near by hospitals, restaurants, temples
• Direction ( route ), Distance, Travel time, Live traffic
• Street view for 3D location
• Geofencing
• Live tracking location
• Get current location
• Put markers on various places

Alternatives of Google map api :

• MapMyIndia (Indian Maps)
• HereMap
• Apple map
• Bing Map

I am using MapMyIndia api due to high cost of Google map apis. I have also implemented here map. Both are nice.

There are two versions of here-map, free and premium. Premium here map service is better than free here map service. I have implemented live tracking of car, replay route, using both apis.

Difference between XIB and Storyboard

Ans : 


XIB :

1) Xib files are used with a single UIView.

3)It's utilizes more memory as compared to storyboard and quiet slow.

4) It is compatible from iOS5 and onwards

5) You can do localizations for different languages and countries using different XIBs .

6) It's difficult to use same Xib to support multiple devices.

Storyboard :

1)You can layout all your Scenes like View Controllers, Nav Controllers, TabBar Controllers, etc in a single storyboard.

3)Usually fast and allocates less memory.

4)It's not compatible prior to iOS 5 .

5)"Dynamic" and "Prototype" cells can be used easily.

6)Storyboards best to use for the apps with a small to medium amount of screens.

Difference between thread-safe and non-thread-safe in iOS

Ans : 

Thread-Unsafe -> If any object allow to modify by more than one thread at the same time.  (non-atomic property is thread-unsafe. Comments are welcomed)

Thread-safe -> If any object not allow to modify by more than one thread at the same time.Immutable objects are generally thread-safe. (atomic property attribute type. Comments are  welcomed)

In general, immutable classes like NSArray, let are thread-safe, while their mutable variants like NSMutableArray,var are thread-unsafe.

Which type of encryption you have used in iOS App?

Ans : I have used trippleDES for passing data in request to server.

NSData *jsonData = [NSJSONSerialization dataWithJSONObject:dicPostDict options:kNilOptions error:&error];

 NSString *strJsonData=[[NSString alloc] initWithData:jsonData encoding:NSUTF8StringEncoding];

 NSData *encryptedJsonString = [CommonMethods tripleDesEncryptString:strJsonData  key:@"2-055PL&okjnnhkey@inihgr" error:nil];
 NSString *strencryptedJsonString = [encryptedJsonString base64Encoding];

Explain MVC through implementation of UITableView

Ans :

Read first about MVC

Let's understand to implement UITableview in MVC

1. We write fetching data query or request web-service and parse json,xml and save data to any global variable like dictionary, array, etc. So all inserting, fetching methods and data variable are comes under M.....Model

2. We make custom tableview cell, and put various types of views like UILabel, UITextField, UIButton for displaying in UITableView on screen. So this comes under V....View.

3. For displaying TableView, we will take UIVIewController or UITableviewController. This are responsible for various activity like telling how many section, rows are there, on delete button deleting row, how much height of cell, etc... So this comes under C....Controller.

Explain Apple push notification working

Ans : Push notifications allow developers to reach users and perform small tasks even when users aren’t actively using an app.

In iOS 10, User can do following task :

• Display a short text message
• Play a notification sound
• Set a badge number on the app’s icon
• Provide actions the user can take without opening the app
• Show a media attachment
• Be silent, allowing the app to wake up in the background and perform a task

Now following steps to follow to configure push notification :

1. Create app id in developer account with your app bundle id. Push notification entitlement must be enabled for this app id. (or another way for go to App Settings > Capabilities and enable push notification switch). You also have to create CSR(Certificate Signing Request) file from your keychain and assign to this app id push notification feature in developer account.

2. Now in terms of coding, first we need to ask to user for allowing user notification. After allowing, we need to register for remote notification. If all goes good, system provides you 'token' which is address of this app for this device.

3. In code, first import usernotification. Then for registering for remote notification, in didFnishLaunchingWithOptions, 

UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge])  {

    (granted, error) in

   

       print("Permission granted: \(granted)")

    

       guard granted else { return }

       self.getNotificationSettings()

  }

 func getNotificationSettings()  {

       UNUserNotificationCenter.current().getNotificationSettings { (settings) in

       print("Notification settings: \(settings)")

       guard settings.authorizationStatus == .authorized else { return }

       UIApplication.shared.registerForRemoteNotifications()

  }

} 

4. If registered for remote notification successfully, then one of the following two method will be called,

func application(_ application: UIApplication,
                 didRegisterForRemoteNotificationsWithDeviceToken deviceToken: Data)  {

       let tokenParts = deviceToken.map { data -> String in
              return String(format: "%02.2hhx", data)
        }

       let token = tokenParts.joined()
       print("Device Token: \(token)")
}

func application(_ application: UIApplication,
                 didFailToRegisterForRemoteNotificationsWithError error: Error)  {
  print("Failed to register: \(error)")
}

5. Device token is provided by APNS and this token will be converted to string. This device token shold be sent to application server or stored to database on server side.

Now lets study about payload or notification message,

Payload looks like :

{
  "aps": {
    "alert": "Breaking News!",
    "sound": "default",
    "link_url": "https://raywenderlich.com"
  }
}

aps is fixed key in payload dictionary json. aps is also dictionary itself.

alert : Display text message
sound : Which sound when notification come
link_url : custom key, we can any such custom key for data
badge : number of count of badge that is displayed on app icon
category : which type of custom action notification have

Payload maximum size is 4096 kb (4 mb).


Now what when notification comes

1. If app is closed didFinishLaunchingWithOptions is called.
2. If open in background or foreground, then didReceiveRemoteNotification is called.

For 1st case,

In didFinishLaunchingWithOptions method
// Check if launched from notification

if let notification = launchOptions?[.remoteNotification] as? [String: AnyObject] {

  let aps = notification["aps"] as! [String: AnyObject]
  _ = NewsItem.makeNewsItem(aps)

  (window?.rootViewController as? UITabBarController)?.selectedIndex = 1
}

For 2nd case,

In didReceiveRemoteNotification,

let aps = userInfo["aps"] as! [String: AnyObject]
  _ = NewsItem.makeNewsItem(aps)

Actionable Notification

Actionable notifications let you add custom buttons to the notification. You can put reply,retweet,like button as you seen our favourite apps. This type of notification can be defined by Category.

In this type notification, we have to register category like following instead of UIApplication.shared.registerForRemoteNotifications().

func registerForPushNotifications() {
  UNUserNotificationCenter.current().requestAuthorization(options: [.alert, .sound, .badge]) {
    (granted, error) in   
    print("Permission granted: \(granted)")
 
    guard granted else { return }
 
    // 1
    let viewAction = UNNotificationAction(identifier: viewActionIdentifier,
                                          title: "View",
                                          options: [.foreground])
 
    // 2
    let newsCategory = UNNotificationCategory(identifier: newsCategoryIdentifier,
                                              actions: [viewAction],
                                              intentIdentifiers: [],
                                              options: [])
    // 3
    UNUserNotificationCenter.current().setNotificationCategories([newsCategory])
 
    self.getNotificationSettings()
  }
}


Above things is not enough for taking action on button. We have to add extension of UNUserNotificationCenterDelegate.

Silent Notification 

If we want to do something task without knowing to user in background, then we can send silent notification to user device. For this background modes of push notification must be checked. For push notification aps, there is key named content-available. That's value should be 1 for silent notification.

For more detail, click here.

What are persistent storage in iOS and Which one is most secure?

Ans : There are SIX types of persistent storage.

1. Userdefaut
2. Property List
3. Sqlite
4. Keychain
5. Files
6. Coredata

If brief answer they asked then follow :

1. Userdefaut : NSUserDefault class allow us to store small amount of data. It can store NSData, NSString, NSArray, NSDictionary,  NSNumber,

The maximum data can we saved depends on iOS. Currently it can store 4GB of data.

But if file is too large, then it takes too much time for retrieve and write data in file. So we can save small amount of data only. Otherwise it waste time.

We can also store our custom objects in userDefaults. We achieve this by conforming our class to NSCoding protocol. We can then convert our custom object into NSData with the help of NSKeyArchiver class. The NSData is then stored into userDefaults like other objects. Similarly we can get NSData from userDefaults and then using NSKeyUnarchiver convert the NSData back to our custom objects.

2. Property List : As userdefaut save data in plist file, so like userdefaut, Property List is not also made for save large amount of data. There is one method of NSArray and NSDictionary as writeToFile for saving data.

3. Sqlite : If your application deals with large amount of data with relationship then we should use sqlite. It's API is written in C language and embedded with our application so it is very fast. There are ORM for bringing gap between obj c app and sqlite like, FMDB,  Realm

4. Keychain : If you want to save highly sensitive and secure data like passwords and secret codes then there is a good news for you. Storing data in keychain is most secure way. To store data, I have taken library named SwiftKeyChainWrapper from cocoapods.

To Save data in Keychain : 

let saveSuccessful: Bool = KeychainWrapper.standard.set("Some String", forKey: "myKey")

To get data from Keychain :

let retrievedPassword: String? = KeychainWrapper.standard.string(forKey: "userPassword")

To remove data from keychain : 

let removeSuccessful: Bool = KeychainWrapper.standard.remove(key: "myKey")

5. Files : You can save data to any type of file. There are three type of folder like Document, Library, Tmp fo saving various type of file.

6. Core Data : Apple’s solution for persistence allows applications to persist data of any form and retrieve it. It  isn’t technically a database, although it usually stores its data in one (an SQLite DB). It’s not an object-relational mapper (ORM), though it can feel like one. It’s truly an object graph, allowing you to create, store, and retrieve objects that have attributes and relationships to other objects. Its simplicity and power allow you to persist data of any form, from basic data models to complex.