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Difference between normal function and function ending throw?

Ans : 

Function ending with throw can throw error but normal function can not throw error it can just return value.

Lets take example :

1. Custom error enum

enum ErrorsToThrow: Error {
    case fileNotFound
    case fileNotReadable
    case fileSizeIsTooHigh
}

2. Make function which can throw error

func readFiles(path:Stringthrows  ->String {
        if path == "" {
            throw ErrorsToThrow.fileNotFound
        }
        return "Data from file"

    }

3. Calling readFiles function
   do {
            let dataFromString = tryreadFiles(path: "")
            print(dataFromString)
        catch ErrorsToThrow.fileNotFound {
            print("error generated1")
        catch ErrorsToThrow.fileNotReadable {
            print("error generated2")
        catch ErrorsToThrow.fileSizeIsTooHigh {
            print("error generated3")
        catch {
                print("error")
        }

Now, let's analysis.

1. If in #2, function is not ending with throws can not throw error. But our function can throw error.
2. In #3, we have used try?, so if readFiles function return nil instead of throwing error. So in our case print(dataFromString) statement executed and it will nil means printing nil.
3. If try! is written and if function throw error, then fatal error will be occured and program will be crashed as we ensure that error will not occur by putting ! .
4. So if we want to execute catch statement then we have to use only try . try always used with do-catch.
5. try? and try! does not need do-catch block.

What is closure? Why we use closure instead of function sometime?

Ans : 

The two most used cases are completion blocks and higher order functions in Swift. 

Completion blocks: for example, when you have some time consuming task, you want to be notified when that task is finished. You can use closures for that, instead of a delegate (or many other things)


func longAction(completion: () -> ()) {
    for index in veryLargeArray {
        // do something with veryLargeArray, which is extremely time-consuming
    }
    completion() // notify the caller that the longAction is finished
}

//Or asynch version
func longAction(completion: () -> ()) {
    
    dispatch_async(dispatch_get_global_queue(DISPATCH_QUEUE_PRIORITY_DEFAULT, 0)) {
        
        for elem in veryLargeArray {
            // do something with veryLargeArray, which is extremely time-consuming
        }
        dispatch_async(dispatch_get_main_queue(), {
            completion() // notify the caller that the longAction is finished
        })
    }
}

longAction { print("work done") }

In the example above, when you have a time consuming task, you want to know when the for loop finishes iterating through the very large array. You put the closure { println("work done") } as an input parameter for the function which will be executed after the for loop finishes its work, and print "work done". And what happened is that you gave a function (closure) to longAction and name it to completion, and that function will be executed when you call completion in longAction.

Sorted method works using closure.

About how sorted (probably) works: So the idea is, that sorted will go through the array, and compare two consecutive elements (i, i + 1) with each other, and swap them, if needed. What does it mean "if needed"? You provided the closure { (s1: String, s2: String) -> Bool in return s1 > s2 }, which will return true if s1 is greater than s2. And if that closure returned true, the sorted algorithm will swap those two elements, and continues this with the next two elements (i + 1, i + 2, if the end of the array is not reached). So basically you have to provide a closure for sorted which will tell "when" to swap to elements.

Understand Closure


Differences between internal testers and external testers in test-flight?

Ans : 

Both internal and external testers will install your app from the TestFlight app. Once invited, they will be sent an email asking them to install the TestFlight app. Once they have done so, they'll be able to install your beta app...
Internal Testers: Think of these users as employees who receive instant updates to your app without approval/review
  • Must be added manually via iTC
  • 25 Max allowed
  • Once your app is uploaded it's available immediately for internal testers (before it has been reviewed)
  • All internal testers must be added as a user in your iTC "Users and Roles" settings, which gives them certain permissions (review other answers and the docs for this). You wouldn't want to give just anyone permissions here.
  • Do not have a 60-day time limit
External Testers
  • Will only be able to use your uploaded build for up to 60 days. If you add additional builds, they can update, and the 60 days starts over again.
  • Will be able to test your app after
    1. You have submitted it for review
    2. It gets approved in TestFlight review and
    3. You set it to be available for testing. The review process us usually instant for new builds with the same version number. If you add a new version number, the review process can take up to 48hrs as of 10/2016.
  • Up to 2000 email addresses can be added. Each email address will allow a user to install the app on multiple devices. The email addresses do not need to match their Apple IDs.
  • They receive an invite to install your app once your first build is available for testing. If you add a new user after making a build available for testing, they'll immediately receive an invite. All users will receive notifications to install newer versions of the app if you upload additional builds.
  • Will be disallowed from using your app after you have pushed it to the official app store (which promptly ends the beta) or 60 days have passed since you started the beta, whichever comes first. If you end the beta without launching in the app store, and they try to open it, it will crash. Yay, Apple UX! If you do push a version to the app store with the same bundleName, version, and bundleID (build number doesn't matter), then your beta testers will automatically receive the app-store version of the app when it goes live.

What are certificates and provisioning profile for uploading app to app store?

Ans : 

Certificates - This is a cryptographic certificate granted to you by Apple.  It works just like SSL where you get a certificate signed by an authority.  Apple signs the private key that you use to sign different pieces of your application.  Different certificates create different types of trust.  Some allow you to sign and submit your application for the App Store, while others allow your application's web server to send push notifications to users via APNS.  In the latter case, for instance, Apple uses this certificate to trust the web server sending the push notification.  Otherwise, it would be easy for an attacker to spoof a valid push notification and spam users.  The most common certificate you would create signs the key you use to deploy your application to a device or submit it to the App Store.

When you create a certificate through Apple's developer portal, you have to create your key pair and send a "Certificate Signing Request," which at first is likely pretty confusing to developers just trying to see their application run on a device.
If you visit the developer portal, you'll find you can create certificates for Development or Distribution.  These certificates are rooted to different authorities, so that the two worlds are never confused (though all iOS devices trust both in a seemingly equal fashion).
Provisioning Profiles - Probably the most confusing component in the system, a provisioning profile indicates the devices for which an application is correctly signed.  If you visit the developer portal, you'll notice you can create two types (again called Development and Distribution).  Provisioning profiles say "applications with this Identifier signed with this Certificate's private key are okay to run on these devices."  Now that you know a provisioning profile is tied to a certificate, you can see why you have to decide whether to create a Development or Distribution profile.  Development profiles are limited to 100 devices.  Distribution profiles can either be Ad-Hoc or App Store distribution profiles.  I am not sure whether Ad Hoc profiles have device limits.
You might ask, then, why not always use a Distribution profile?  It can deploy to an unlimited number of devices, and is still attached to a certificate owned by the developer.  Another piece of Apple's security puzzle are Entitlements.  In an iOS application's bundle, you'll find Entitlements.plist, which is a list of capabilities that an application wants.  When signing your application using a certificate intended for distribution, Xcode (really the signing utility) will not allow an entitlement with get-task-allow set to YES.  This is because get-task-allow is what allows a debugger to connect to a process, and Apple doesn't want that happening on apps meant for distribution.


Short Ans : 

1. A Certificate authenticates you as an entity. It can represent you as an individual, or your company.
2. The Identifier is a unique ID for your mobile app.
3. A provisioning profile associates your certificate with the App ID. It is the link between #1 and #2 above.



What is MLKit?

Ans : 

ML Kit is a mobile SDK that brings Google's machine learning expertise to Android and iOS apps in a powerful yet easy-to-use package.

Use : 

  • Text Recognition API to detect text in images 
  • Face Contour API to identify facial features in images 
  • Cloud Text Recognition API to expand text recognition capabilities (such as non-Latin alphabets) when the device has internet connectivity .
  • Learn how to host a custom pre-trained Tensor Flow Lite model using Firebase 
  • Custom Model API to download the pre-trained TensorFlow Lite model to your app Use the downloaded model to run inference and label images

What is handshaking process?

Ans :

Handshaking is an automated process that sets parameters for communication between two different devices before normal communication begins. Much like the way a human handshake sets the stage for the communication to follow, the computing handshake provides both devices with the basic rules for the way data is to be shared between them. These rules can include transfer rate, coding alphabet, parity, interrupt procedure and more.

What is Enumeration in Swift?

Ans : 

An enumeration defines a common type for a group of related values and enables you to work with those values in a type-safe way within your code.
Enumerations offer an easy way to work with sets of related constants. An enumeration, or Enum, is a symbolic name for a set of values. Enumerations are treated as data types, and you can use them to create sets of constants for use with variables and properties.

When to use enum?
Whenever a procedure accepts a limited set of variables, consider using an enumeration. Enumerations make for clearer and more readable code, particularly when meaningful names are used.

The benefits of using enumerations include:

  • Reduces errors caused by transposing or mistyping numbers. 
  • Makes it easy to change values in the future. 
  • Makes code easier to read, which means it is less likely that errors will creep into it. 
  • Ensures forward compatibility. With enumerations, your code is less likely to fail if in the future someone changes the values corresponding to the member names.



What are the app id and bundle identifier?

Ans : 
Bundle ID : 
A bundle ID or bundle identifier uniquely identifies an application in Apple's ecosystem. This means that no two applications can have the same bundle identifier. To avoid conflicts, Apple encourages developers to use reverse domain name notation for choosing an application's bundle identifier.
i.e com.iosiqa.newapp or com.iosiqa.app.new

App ID : App ID consists of Team ID + Bundle ID. Team ID is provided by apple to one team in developer account.
i.e ABC12345.com.iosiqa.newapp

What is use of APP ID? 
Whenever you want to enable a capability or application service for your application, you enable that capability for the App ID your application is linked to. This used to be tedious, requiring a visit to Apple's developer website. Xcode has evolved quite a bit over the years and it takes care of the details most of the time.

How To declare custom tableview cell? What Is The Use Of dequeuereusablecellwithidentifier ?

Ans : 

Let's create custom cell :

1. Take viewcontroller or tableviewcontroller
2. In Tableview, put one uitableviewcell and change style to custom.
3. Give any string (i.e "newcell") to reuseidentifier of cell in attribute inspector.
4. Put labels, textfields, views in cell according to your need.
5. Add new file named as newCell.swift that inherit from UITableViewCell.
6. Select your cell and give class name newCell.
7. Now you can make outlet of that cell in newCell.swift.

Here magic will be created using dequeuereusablecellwithidentifier : 

The best part of using dequeueReusableCellWithIdentifier is that using this you can re-use your cells.

Imagine if your table has 1000 entries. Now, if for each entry a table cell would be created then for 1000 entries, 1000 tableview cells and memory allocation for 1000 tableview cells.

App will be slowed down or would crash if the entries goes beyond 1000.

When we use, dequeueReusableCellWithIdentifier, the tableView just creates exactly the number of cells based on your table height and cell height. Suppose, if it shows 4 cells in the tabelView and rest you can see by scrolling, then memory for only 4 cells would be allocated at any given point of time.

Now, when you will scroll the tableView, it will re-use the same cell but will change the cell content (data) based on your data source.

Hope this clears your doubt.

Code

- (UITableViewCell *)tableView:(UITableView *)tableView cellForRowAtIndexPath:(NSIndexPath *)indexPath
{
    UITableViewCell *cell =[tableView dequeueReusableCellWithIdentifier:"newcell"];
    cell.textLabel.text = @"Test";
    return cell;

}

Difference between App Bundle and File Directory

Ans : Although bundles and packages are sometimes referred to interchangeably, they actually represent very distinct concepts:

1.
A package is any directory that the Finder presents to the user as if it were a single file.
A bundle is a directory with a standardized hierarchical structure that holds executable code and the resources used by that code.

2.
The Finder considers a directory to be a package if any of the following conditions are true:
.The directory has a known filename extension: .app, .bundle, .framework, .plugin, .kext, and so on.
.The directory has an extension that some other application claims represents a package type; see Document Packages.

Difference between array, set and dictionary

Ans : 

Array :
Arrays are effectively ordered lists and are used to store lists of information in cases where order is important.
Cost of adding item in array is greater than set and dictionary if item is not appending first.

For example, posts in a social network app being displayed in a tableView may be stored in an array.

Set : 
Sets are different in the sense that order does not matter and these will be used in cases where order does not matter. Sets are especially useful when you need to ensure that an item only appears once in the set.

Dictionary : 
Dictionaries are used to store key, value pairs and are used when you want to easily find a value using a key, just like in a dictionary.


For example, you could store a list of items and links to more information about these items in a dictionary.


What is NSPredicate?

Ans : Using NSPredicate, we can filter records before fetching from Coredata or collections. It work in place of where clause in sql.

NSPredicate on Core Data :

When we want data from coredata of only who's name is Manan Shah. So using predicate we can filter as following :

var strName = "Manan Shah"
request.predicate = NSPredicate(format: "name = %@", strName)

NSPredicate on Collections : 

let manan = Person(firstName: "Manan", lastName: "Shah", age: 28)
let sagar = Person(firstName: "Sagar", lastName: "Shah", age: 26)

let people = [manan, sagar] as NSArray

let thirtiesPredicate = NSPredicate(format: "age >= 27")

people.filtered(using: thirtiesPredicate)
Result : manan object will be return.

What is safe area?

Ans: The Safe Area Layout Guide helps avoid underlapping System UI elements when positioning content and controls.

The Safe Area is the area in between System UI elements which are Status Bar, Navigation Bar and Tool Bar or Tab Bar. So when you add a Status bar to your app, the Safe Area shrink. When you add a Navigation Bar to your app, the Safe Area shrinks again.

On the iPhone X, the Safe Area provides additional inset from the top and bottom screen edges in portrait even when no bar is shown. In landscape, the Safe Area is inset from the sides of the screens and the home indicator.

The layout guide (Safe area) representing the portion of your view that is unobscured by bars and other content. In iOS 11+, Apple is deprecating the top and bottom layout guides and replacing them with a single safe area layout guide.

In iPhone X portrait, safe area insets from top(notch) and bottom(home) side, and
in landscape, left(notch/ home bar) and right side(home bar/notch) and also bottom side.

We can enable using of safe area layout guide property of view controller from class inspector.

Difference between SOAP and REST

Ans : 

1. Requests sent via REST tend to be much lighter than SOAP. Because of this, applications don't require much bandwidth to use REST web services over SOAP.

2. REST is good when working with web services open to the public, but if security is required, then the SOAP API is better to use. 

3. SOAP permits XML data format only while REST permits Plain text, HTML, XML, JSON etc.

i.e 

Suppose we want to retrieve today's weather report from a server which is providing weather information, your RESTful URL will look something like http://weatherdata.org/data/weather/uk/london (Not real link just example url), which is very similar to HTTP request like http://weatherdata.org/data/weather?q=uk,London.

On the other hand, in order to get the same data using SOAP, you need to create an XML message with header and body and send it http://www.webservicex.net/globalweather.asmx?op=GetWeather

In short, RESTfull web services are much simpler, flexible and expressive than SOAP web services in Java.

How many ways we can present view controller?

Ans : 

There are only 2 options to display one viewcontroller2 from viewcontroller1. It is depend on what we want to achieve.

1.Modal Presentation : Use this only viewcontroller2 should take focus away from viewcontroller1 entirely until it is dismissed.

[self presentViewController:viewController2 animated:YES completion:nil];

ViewController2's presenting viewcontroller is ViewController1.
ViewController1's presented viewcontroller is ViewController2.

UIAlertViewController is working on this way.

2. ViewController Containment : Use this if you want to display viewcontroller1's some view in which viewcontroller2's shows. So if there are 4 views, then in 4 views of viewcontroller1, we can show 4 different viewcontroller.

[self addChildViewController:viewController2];
[self.view addSubview:viewController2.view];
[viewController2 didMoveToParentViewController:self];

So here viewcontroller2's parent viewcontroller is viewcontroller1.
But viewcontroller1's child viewcontroller array contrains viewcontroller2.

UINavigationViewController is working on this way.

So interviewer ask questions about presented viewcontroller, parentviecontroller.

But in 1st way, parent viewcontroller is nil.
in 2nd way, presented viewcontroller, presenting viewcontroller is nil.

What is retain cycle or strong cycle?

Ans : 

According to ARC, variable should be one of three Strong, Weak or unowned. By default, variable has strong reference.

Let's take example :

class Employee {
var name  : String
var emid  : String
var title : String
init(name: String,emid: String, title: String) {
           self.name = name
   self.emid = emid
   self.title = title
        }

        deinit {
print("Employee : \(name) removed")
}
}

var manan : Employee? = Employee(name: "Manan", emid: "1234", title: "Sr iOS Developer")
manan = nil

Here deinit will be called and output will be "Employee Manan removed"

Now we add reference :

var sagar = manan
manan = nil

Here deinit will not be called due to adding reference. Here sagar has strong reference to variable which owned by manan before.

Now,

var sagar = manan
manan = nil
sagar = nil

Here deinit will be called and again output will be "Employee Manan removed"


Now let's discuss about Strong cycle :

Strong cycle occurs when two object has strong reference to each other. i.e objectA has strong reference to objectB and objectB has strong reference to objectA.


example :

class Employee {
var name  : String
var emid  : String
var title : String
var macBook : MacBook?
init(name: String,emid: String, title: String) {
           self.name = name
   self.emid = emid
   self.title = title
        }

        deinit {
print("Employee : \(name) removed")
}
}

class MacBook {
var serialNumber: String
var assignee : Employee?
        init(serialNumber: String) {
              self.serialNumber = serialNumber
        }

deinit {
print("Macbook : \(serialNumber) removed")
}
}

var manan : Employee? = Employee(name: "Manan", emid: "1234", title: "Sr iOS Developer")
var mac : MacBook? = MacBook(serialNumber: "ABC123")
manan?macBook= mac
manan = nil
mac = nil

Here, output :

Employee Manan removed
Macbook ABC123 removed

Why? Because here there is no strong reference from both side. So retain cycle is not yet created.

Now,

var manan : Employee? = Employee(name: "Manan", emid: "1234", title: "Sr iOS Developer")
var mac : MacBook? = MacBook(serialNumber: "ABC123")
manan?macBook= mac
mac?.assignee = manan
manan = nil
mac = nil

Output will be :

Nothing will be removed. Not output comes. Because of retain cycle. So there are strong relationship between both objects like manan has mac and mac is assigned to manan.

So, if we want to solve this problem we have to use weak or unowned reference for one side.

So,

weak var assignee : Employee?

Now output will be :

Employee Manan removed
Macbook ABC123 removed

So Now unowned : It is same as weak as it does not hold strong relationship with object. So when to use unowned : An unowned reference is used when the other instance has the same lifetime or a longer lifetime.

Difference between weak and unowned :


  • weak reference is used where there is possibility for that reference to become nil at some point during its lifetime. 
  • An unowned reference is used where there is no possibility for that reference becoming nil at any point until the self-object exist.
Example :

Every employee may or may not hold ICard but every ICard must be assigned to some one.
So Employee class has ICard variable as optional, but in ICard class, employee variable with optional and weak is not possible. If we want to use weak, we should make employee variable in ICard class optional. But we don't want that.

So, solution is that : 

unowned var employee : Employee

Now we are cleared about strong, weak and unowned and also our question : Retain Cycle or Strong Cycle.

Credit : Vinod Shwami

Application States

Ans : 

Before iOS 4.0 there were 3 states. Not running, inactive and active.

  1. Non-running - The app is not running.
  2. Inactive - The app is running in the foreground, but not receiving events. An iOS app can be placed into an inactive state, for example, when a call or SMS message is received.
  3. Active - The app is running in the foreground, and receiving events.
  4. Background - The app is running in the background, and executing code.
  5. Suspended - The app is in the background, but no code is being executed.
For maintaining above states, there are following app delegate methods:


application:willFinishLaunchingWithOptions (First method)
Method called when the launch process is initiated. This is the first opportunity to execute any code within the app.

application:didFinishLaunchingWithOptions
Method called when the launch process is nearly complete. Since this method is called is before any of the app's windows are displayed, it is the last opportunity to prepare the interface and make any final adjustments.

applicationDidBecomeActive
Once the application has become active, the application delegate will receive a callback notification message via the method applicationDidBecomeActive.

This method is also called each time the app returns to an active state from a previous switch to inactive from a resulting phone call or SMS.

applicationWillResignActive
 Each time a temporary event, such as a phone call, happens this method gets called. It is also important to note that "quitting" an iOS app does not terminate the processes, but rather moves the app to the background.

applicationDidEnterBackground
This method is called when an iOS app is running, but no longer in the foreground. In other words, the user interface is not currently being displayed. According to Apple's UIApplicationDelegate Protocol Reference, the app has approximately five seconds to perform tasks and return. If the method does not return within five seconds, the application is terminated.

applicationWillEnterForeground
This method is called as an app is preparing to move from the background to the foreground. The app, however, is not moved into an active state without the applicationDidBecomeActive method being called. This method gives a developer the opportunity to re-establish the settings of the previous running state before the app becomes active.

applicationWillTerminate
This method notifies your application delegate when a termination event has been triggered. Hitting the home button no longer quits the application. Force quitting the iOS app, or shutting down the device triggers the applicationWillTerminate method. This is the opportunity to save the application configuration, settings, and user preferences.