What is better, Force unwrapping or optional binding?

Ans :

Force unwrapping :  It's the action of extracting the value contained inside an Optional. This operation is dangerous because you are telling the compiler: I am sure this Optional value does contain a real value, extract it!

let anOptionalInt: Int? = 1
let anInt: Int = anOptionalInt!

But here if, anOptionalInt has nil value, then fatal error will be generated. Unexpectedly found nil while unwrapping an Optional value.

Optional Binding: Using if let, we can store value in one variable if value is not nil. By this way, fatal error never be generated. This way will be used when we are not sure that variable has value or nil. This method is better because no chances of crashing app.

if let tempStockCode = stockCode {
    let message = text + tempStockCode
    println(message)
}

Implicitly unwrapped optionals : 

let anOptionalInt: Int! = 1
let anInt: Int = anOptionalInt

anOptionalInt is never be optional. But it can has value of nil.

How much memory will be occupied by integer computed property?

Ans :

No memory will be allocated for computed property. Computed property just compute value and return value. It is not stored any where.

Difference between encapsulation and abstraction.

Ans :

Encapsulation hides variables or some implementation that may be changed so often in a class to prevent outsiders access it directly. They must access it via getter and setter methods.

Abstraction is used to hiding something too but in a higher degree(class, interface). Clients use an abstract class(or interface) do not care about who or which it was, they just need to know what it can do.

Encapsulation: Wrapping code and data together into a single unit. Class is an example of encapsulation, because it wraps the method and property. 

Abstraction: Hiding internal details and showing functionality only. Abstraction focus on what the object does instead of how it does. It provides generalized view of classes.

int number = 5;
string aStringNumber = number.ToString(); 

Here, ToString() is abstraction. And how this mechanism number variable converted to string and initialize into aStringNumber is encapsulation.

We can achieve abstraction using protocol in iOS, achieve encapsulation using access control in class or struct.

How to do geo fencing?

Ans :

Geo-Fence : A Geo-fence is a technology that defines a virtual boundary around a real world geographical area. Every time the user enters or exits the boundary of a certain geofence, actions can be triggered in a location enabled device (often a smartphone). Usually the user will receive a notification with certain information based on its location in real time.

Let's implement : 

In order to work with geofences we need to import CoreLocationframework. After that, we define a locationManager in our viewController and we make the viewController a CLLocationManagerDelegate:

 var locationManager : CLLocationManager = CLLocationManager()

Next, we have to define a region with a center (latitude and longitude) and a radius to monitor. As an example, we are going to define a circular region around the beach in Playa Grande, Mar del Plata with a radius of 400 metres:

 func setUpGeofenceForPlayaGrandeBeach() {

  let geofenceRegionCenter = CLLocationCoordinate2DMake(-38.028308, -57.531508);

  let geofenceRegion = CLCircularRegion(center: geofenceRegionCenter, radius:  400, identifier: "PlayaGrande");

  geofenceRegion.notifyOnExit = true;

  geofenceRegion.notifyOnEntry = true;

  self.locationManager.startMonitoring(for: geofenceRegion)

 }

After creating the region, we are going to set the flags notifyOnExit and notifyOnEntry to true . This will make the CLLocationManagerDelegate trigger a notification each time the user enters or exits the geofenceRegionin the following methods:

func locationManager(_ manager: CLLocationManager, didEnterRegion region: CLRegion) {

  print("Welcome to Playa Grande! If the waves are good, you can try surfing!")

//Good place to schedule a local notification

}

func locationManager(_ manager: CLLocationManager, didExitRegion region: CLRegion) {

print("Bye! Hope you had a great day at the beach!")

//Good place to schedule a local notification

}

We are still missing the part when the user has to give authorization to the app to track it’s location. So in our viewController we add the following lines to the viewDidLoad method:

 override func viewDidLoad() {

  super.viewDidLoad()

  self.locationManager.requestAlwaysAuthorization()

  self.locationManager.delegate = self

 }

When the user gives authorization to the app, a delegate method is triggered and if the user has given  authorization, we should set up the geofence and start monitoring the region.

 func locationManager(_ manager: CLLocationManager, didChangeAuthorization status: CLAuthorizationStatus) {

  if (status == CLAuthorizationStatus.authorizedAlways) {

    self.setUpGeofenceForPlayaGrandeBeach()

  }

 }

As a last step, we need to add a key to the info.plist with the string to be displayed when asking for location authorization:

<key>NSLocationUsageDescription</key>
<string></string>
<key>NSLocationWhenInUseUsageDescription</key>
<string></string>

Usage of geo-fence in Marketing, Reminders, Child Tracking, Vehicle Tracking, Security, Certain area entry and exit.

What will happened if I delete pod.lock file?

Ans : After first time run pod install, Podfile.lock will be generated.

The purpose of Podfile.lock is tracking of every version of every library that Cocoapods has installed for you, especially working together with a team.

In team there are two guys working, Narendra and Amit.

• Narendra has made project and install library named Demo Library Version 1.3.3
• After some days, Demo Library is updated to 1.4.0. and Narendra not hit command pod update  as he is happy with 1.3.3
• Amit copy narendra's project and hit command pod install, then 1.4.0 will be installed(if Podfile.lock is not there).
• So here is how Podfile.lock work, record the version of what Narendra had installed, then cocoapods will check what version Narendra had installed and then install on Amit's project. (1.3.0)
• But if Amit hit command pod update, then in pod.lock file, version changed to 1.4.0 .

So Podfile.lock file should not be deleted if we work on team. And so Podfile.lock file should be checked while using source control.

Everyone should take care while hitting command pod install and pod update. Choose wisely between those. While update pod update, we should ask to our teammate.

Another nice feature is cocoapods will create a snapshot of every library while using source control.

Understand from : Video