Multiple option interview questions

What is the first method called in the iOS App initialisation flow? & what is the return type?

• Main, , Return the is void.
• App Delegate, Return type is Bool
• UIApplicationMain, Return type is Bool
• Main, Return type is int.

What is the parent class of App Delegate?

• UIResponder
• NSObject
• UIApplicationMain
• UIKit

What is the difference between [Foo new] and [[Foo alloc] init]?

• New will not always initialize the object.
• New is significantly faster than alloc + init.
• None, they perform the same actions.
• New does not exist in Objective-C.

What happens at runtime with the following :

    NSObject *obj1 = nil;

    NSObject *obj2 = [obj1 copy];

    NSLog(@"value of object 2  %@",obj2);

• Application crashes with “SIGABRT”
• Application continues, but issues “cannot access nil object reference” warning
• Object 2 is instantiated as an NSObject with nil Values
• Log prints “(null)” and continues as usual

What is the object.toString equivalent in Objective-C?

• [NSObject toString];
•  [NSObject description];
• [NSObject stringWithFormat];
•  [NSObject getDescription];

The format for a NSPredicate is the same as a Regular Expression

• True
• False

What can happen if you use “self” inside a block?

• None of the above.
• Self can become dangling pointer.
• You can create a retain cycle.
• By the time the block executes, self can be pointing to a different object[NSObject toString]

What is @dynamic directive meaning in iOS?

• The @dynamic directive generates the accessor methods for you at compile time.
• The @dynamic directive tells the compiler that you will provide accessor methods dynamically at runtime.
• The @dynamic directive generates a getter method for your property at compile time.
• The @dynamic directive generates a getter method for your property at run time.

You can use %@ to specify a dynamic property

• True
• False

What is difference between #import and #include?

• #import ensures that a file is only ever included once, and #include allows the same thing.
• None, they do the same thing.
• #include is not valid syntax.
• #include ensures that a file is only ever included once and #import permits the file to be included many times.

A UIView is a superclass of:

• UIViewController
• UIWindow
• UIImage
• UILabel
• UIScreen

A method and a variable can have the same name in Objective C.

• True
• False

What framework is KVO (Key Value Observing) a part of?

• Foundation
• UIKit
• CoreData
• UIKItCore

What class method is used to make an NSArray from NSData class?

• NSArray arrayWithObject:
• NSArray dataWithContentsOfFile:
• NSData dataWithContentsOfFile:
• NSKeydUnarchiver unarchiveObjectWithData:

In Core Data, what is the name of the object representation for the database schema?

• NSManageObjectContext
• NSManagedObjectModel
• NSEntityDescription
• NSManagedObject

What’s the difference between “nil” and “NULL” ?

• nil is a literal null value for Objective-C instances. NULL is object used to represent null.
•  nil is a literal null value for Objective-C instances. NULL is literal null value for Objective-C classes.
• Nil is a literal null value for Objective-C instances. NULL is literal null value for C pointers.
• NULL is literal null value for Objective-C instances. Nil is literal null value for C pointers
• they are the same thing

Which of the following is Singleton class?

• NSFileManager
• UIApplication
• NSFileManger & UIApplication
• NSArray & NSDictionary
• NSString & NSOperations

What is the output of the below program?

    NSMutableString *tempString = [NSMutableString stringWithString:@"1"];

    dispatch_async(dispatch_get_main_queue(), ^{

        [tempString appendString:@"2"];

        NSLog(@"%@",tempString);

    });

    [tempString appendString:@"3"];

    NSLog(@"%@",tempString);

• Log prints “13” & “132” and continues as usual.
• Log prints “12” and then we will have a deadlock here because the main queue will block.
• Log prints “123” and continues as usual.
•  Log doesn’t print anything. It’s deadlock here because the main queue will block on the call to dispatch_async.

What is the output of the below program?

    NSMutableString *tempString = [NSMutableString stringWithString:@"1"];

    dispatch_sync(dispatch_get_main_queue(), ^{

        [tempString appendString:@"2"];

        NSLog(@"%@",tempString);

    });

    [tempString appendString:@"3"];

    NSLog(@"%@",tempString);

• Log prints “13” & “132” and continues as usual.
• Log prints “12” and then we will have a deadlock here because the main queue will block.
• Log prints “123” and continues as usual.
•  Log doesn’t print anything. It’s deadlock here because the main queue will block on the call to dispatch_async.

What is used to sort Core Data results?

• NSSort
• NSCoreDataSort
• [self sort]
• NSSortDescriptor
• NSPredicate

Note : Answer is written in Bold.

GIT for Interview

1. Difference between Distributed & Central version control system.
A. GIT is distributed version control system.
     SVN is central version control system.

Central Version Control System : It is located in one place and people can check out from central location to make their changes and then check everything back in but some times it is problematic if central repository is corrupted or central system is not connected through network. For that we have to take backup manually in local machine.

Distributed Version Control System : Everybody has local repository. Your local repository has all information that remote repository has and till last sync done between local and remote repository. So sometimes, if remote repository is not able to be connected through internet, then we can see every changes as it is also saved in local repository. So every developer has repository in locally. So it is called in distributed version control system.


 2. Check version of GIT installed on your machine.
A. git --version

3. Setting configuration
A.
Set username : git config --global user.name "Manan Shah"
Set email : git config --global user.email "manan0shah@gmail.com"
Check configuration setting : git config --list

4. Get git function help
A.

git help <verb>
git verb --help

i.e git help config
     git config --help

     git help add
     git add -help

5. Setup git in your project
A. Goto finder/folder of project which we want to track, using terminal using cd command and write following command
 git init

6. To check status of untracked files in our repository
A. git status

7. Ignore files which we want to keep untracked. Like personal settings, preferences, etc
A. Create a gitignore file : touch .gitingore
     Write down list of files which we want to ignore to track as below :
     .ds_store
     .xcodeproj
     *.py  (wild card used to ignore files which has py extension)

After this, git status

--------------------------------------------

There are 3 area in area we have knowledge about.
1. Working directory
2. Staging Area
3. Git directory

(image from Pro Git" book : https://git-scm.com/book/en/v2)

1. Working directory : Untracked files reside in working directory. -> Files in red colour in terminal
2. Staging Area : When we use command git add . , then this files added to staging area. Which can be committed. -> Files in green colour in terminal
3. Git directory : When we commit our changes, then it goes to git directory. That can be push to remote directory. git commit -m "message for this commit like changes in setting"

Note : If we want to uncommit changes or remote files from staging area to working directory, then Use git reset 

We can check all commit log using command : git log

------------------------------------------

Cloning git repo

git clone <url_of_remote_git> <local_directory>

git clone https://....../remote_repo.git .    (. means in current folder)

-----------------------------------------

Viewing remote repository info

git remote -v  : Give information about your local repository path for fetch, push

git branch -a : Give list of all local and remote branches

-----------------------------------------

Pushing code

git diff : tells difference between remote and local files changes
git pull origin master : pull all changes made from remote repo to local
git push origin master : push all changes from local to remote repo

-----------------------------------------

Merge branch

Suppose, we have worked on calc branch and we need to merge calc branch into master branch.

git checkout master :  Switch to master branch or in which we have to merge
git pull origin master : Pull all changes in master branch from remote server
git branch --merged : Check branch name in which code is to be merged
git merge calc : Merge calc branch with master branch. It shows number of changes. If any conflicts are there, then  we have to solve it using editing code.
git push origin master : Push merged code to remote master branch

-----------------------------------------

Deleting branch

git branch -d calc : Delete calc branch locally
git branch -a : To check whether branch is deleted or not.
git push origin --delete calc : To delete calc branch remotely

-----------------------------------------------------------------------------------------------------------------

Different parameters for adding files to staging area  :

1. git add -A or git add --all (Default): adding all files from leading directory into staging area
2. git add -A my_dir/ or git add my_dir/ : adding only files located in my_dir into staging area
3. git add -u : adding only modified files into staging area
4. git add -u my_dir/ : adding only updated files located in my_dir into staging area
5. git add . : adding all files in current directory into staging area
6. git add .gitignore : Add only specific file into staging area.

Difference between git add -A and git add . : git add -a add all files in leading directory and git add . only add files from current directory.

-----------------------------------------------------------------------------------------------------------------

Switch to branch without commiting

git stash save "worked on save function" : It will save this branch at this point without commited. And this branch at initial stage.
git stash list : List all stashes here
stash@{0} : On add : worked on save function
git stash apply stash@{0} : Come to our point back using this command. stash will not be dropped.
git stash pop : Come to our point back & drop stash from list.
git stash drop stash@{0} : drop stash@{0}
git stash clear : Clear all stash in list

If we want to do changes from one branch to another branch, then this is most wanted method.

Suppose, I have changed code in master branch.  But I want it to CalC branch. Then,
git stash save "add function" :  save stash on master branch
git checkout CalC :  Switched to CalC branch
git stash pop : apply changes
git add . : add files to staging area
git commit -m "intr" : commit & push


Note : New stash come at top position. Always at 0th position. @{0}.

-----------------------------------------------------------------------------------------------------------------

Git difftool & mergetool

git diff : It shows modification with red(Previous) and green(Current) colour content between previous and current file on terminal window. It is very hard to see where we have changed or what word we have changed. Because git diff shows full line instead of changed word.

So instead of using, there are many diff tool and merge tool available. I,e DiffMerge
Using this tool, we can easily find changes and solve if any conflicts are there just because it is graphically represent instead of just terminal.
For that we have to download and install that tool and configuration with our git. After configuration, check configuration using git config --global --list

Check
diff.tool = diffmerge
merge.tool = diffmerge

happened or not?

Now,
to run that diff tool ,
git difftool : It required permission to open diff tool, press Y to open difftool, and we can see modification clearly with color and word by word.

We can take changes according to we required by simply click on which changes and from which file(previous or current).

git mergetool : To merge branch. If any conflict occur, we can easily solve using this type tool due to visual representation.

-----------------------------------------------------------------------------------------------------------------

To change last commit message,

git commit --amend -m "new message" : It will change message of last commit message.

Hight thank full to Corey Schafer

I took help from following videos  :

1. Git Tutorial for Beginners: Command-Line Fundamentals
2. Git Tutorial: Fixing Common Mistakes and Undoing Bad Commits
3. Git Tutorial: Using the Stash Command
4. Git Tutorial: Diff and Merge Tools
5. Git Tutorial: Change DiffMerge Font-Size on Mac OSX
6. Git Tutorial: Difference between "add -A", "add -u", "add .", and "add *"

If you have any doubts for git, please comment on this blog. 

How to call segue programmatic?

Ans : 

For segue first, We have to set identifier in Class Inspector right side in XCode. Through that identifier, we can call like

performSegue(withIdentifier: "identifier", sender: nil) 

What is Content Hugging and Content Compression Resistance Priority?

Ans : 

The priority really come in to play only if two different constraints conflict. The system will give importance to the one with higher priority. So, Priority is the tie-breaker in the autolayout world.

1. Content Hugging Priority : 

Larger the content hugging priority , the views bound will hug to the intrinsic content more tightly preventing the view to grow beyond its intrinsic content size. Setting a larger value to this priority indicates that we don’t want the view to grow larger than its content.

In above example, we set both label leading, trailing, top and bottom but not set width constraint. So here conflicts will occur. You can see red line between two label showing conflict.

Solution : If we have label's content hugging priority higher than there will be no conflicts as hight priority label will not grow its size more than its content size. See below image :

Blue label has more content hugging priority (251) than green label(250). Blue label's width will be set fixed as its content size.

2. Content Compression Resistance : 

Setting a higher value means that we don’t want the view to shrink smaller than the intrinsic content size. It's simple : Higher the priority means larger the resistance to get shrunk.

Example . One button having large name and auto layout is set on button as its width is become 40. So, button's content is not readable. See image :

Button horizontal compression resistance is 750 and width constraint priority is 1000.

For Solution, let's change horizontal compression resistance to 1000 and width constraint priority less than 1000 i.e 999 . Now see effect on below image :

Button horizontal compression resistance is 1000 and width constraint priority is 999.

If you have any comment, question, or recommendation, feel free to post them in the comment section below!

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 : 

What is enum?

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 an 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.