ios questions

Question 1

How could you set up Live Rendering?

Answer 1

The attribute @IBDesignable lets Interface Builder perform live updates on a particular view. IBDesignable requires Init frame to be defined as well in UIView class.

Question 2

What is the difference between Synchronous & Asynchronous task?

Answer 2

Synchronous: waits until the task have completed

Asynchronous: completes a task in the background and can notify you when complete

Question 3

Explain Compilation Conditions

Answer 3

Compilation Conditions to use if DEBUG … endif structure to include or disable given block of code ve separate targets.

Question 4

What is made up of NSError object?

Answer 4

There are three parts of NSError object a domain, an error code, and a user info dictionary. The domain is a string that identifies what categories of errors this error is coming from.

Question 5

What is Enum or Enumerations?

Answer 5

Enum is a type that basically contains a group of related values in the same umbrella but case-less enum won’t allow us to create an instance.

Question 6

What is the bounding box?

Answer 6

The smallest rectangle completely containing all points in a path

Question 7

Why don’t we use strong for enum property in Objective-C?

Answer 7

Because enums aren’t objects, so we don’t specify strong or weak here.

Question 8

What is @synthesize in Objective-C?

Answer 8

synthesize generates getter and setter methods for your property.

Question 9

What is @dynamic in Objective-C?

Answer 9

We use dynamic for subclasses of NSManagedObject. @dynamic tells the compiler that getter and setters are implemented somewhere else.

Question 10

Why do we use synchronized?

Answer 10

synchronized guarantees that only one thread can be executing that code in the block at any given time.

Question 11

What is the difference strong, weaks, read only and copy?

Answer 11

strong, weak, assign property attributes define how memory for that property will be managed.

Strong means that the reference count will be increased and the reference to it will be maintained through the life of the object

Weak ( non-strong reference ), means that we are pointing to an object but not increasing its reference count. It’s often used when creating a parent child relationship. The parent has a strong reference to the child but the child only has a weak reference to the parent.

Every time used on var
Every time used on an optional type
Automatically changes itself to nil

Read-only, we can set the property initially but then it can’t be changed.

Copy means that we’re copying the value of the object
when it’s created. Also prevents its value from changing

Question 12

What is Dynamic Dispatch?

Answer 12

Dynamic Dispatch is the process of selecting which implementation
of a polymorphic operation that’s a method or a function to call at run time. This means, that when we wanna invoke our methods like object method. but Swift does not default to dynamic dispatch

Question 13

What’s Code Coverage?

Answer 13

Code coverage is a metric that helps us to measure the value of our unit tests.

Question 14

What’s Completion Handler?

Answer 14

Completion handlers are super convenient when our app is making an API call, and we need to do something when that task is done, like updating the UI to show the data from the API call. We’ll see completion handlers in Apple’s APIs like dataTaskWithRequest and they can be pretty handy in your own code.
The completion handler takes a chunk of code with 3 arguments:(NSData?, NSURLResponse?, NSError?) that returns nothing: Void. It’s a closure.
The completion handlers have to marked @escaping since they are executed some point after the enclosing function has been executed.

Question 15

How to Prioritize Usability in Design ?

Answer 15

Broke down its design process to prioritize usability in 4 steps:

Think like the user, then design the UX.

Remember that users are people, not demographics.

When promoting an app, consider all the situations in which it could be useful.

Keep working on the utility of the app even after launch.

Question 16

What’s the difference between the frame and the bounds?

Answer 16

The bounds of a UIView is the rectangle, expressed as a location (x,y) and size (width, height) relative to its own coordinate system (0,0).
The frame of a UIView is the rectangle, expressed as a location (x,y) and size (width, height) relative to the superview it is contained within.

Question 17

What is Responder Chain ?

Answer 17

A ResponderChain is a hierarchy of objects that have the opportunity to respond to events received.

Question 18

What is Regular expressions?

Answer 18

Regular expressions are special string patterns that describe how to search through a string.

Question 19

What is Operator Overloading?

Answer 19

Operator overloading allows us to change how existing operators behave with types that both already exist. Operators are those little symbols like +, *, and /

Question 20

What is TVMLKit?

Answer 20

TVMLKit is the glue between TVML, JavaScript, and your native tvOS application.

Question 21

What is Platform limitations of tvOS?

Answer 21

First, tvOS provides no browser support of any kind, nor is there any WebKit or other web-based rendering engine you can program against. This means your app can’t link out to a web browser for anything, including web links, OAuth, or social media sites.
Second, tvOS apps cannot explicitly use local storage. At product launch, the devices ship with either 32 GB or 64 GB of hard drive space, but apps are not permitted to write directly to the onboard storage.
tvOS app bundle cannot exceed 4 GB.

Question 22

What is Functions?

Answer 22

Functions let us group a series of statements together to perform some task. Once a function is created, it can be reused over and over in your code. If you find yourself repeating statements in your code, then a function may be the answer to avoid that repetition.
Pro Tip, Good functions accept input and return output. Bad functions set global variables and rely on other functions to work.

Question 23

What is ABI?

Answer 23

ABIs are important when it comes to applications that use external libraries. If a program is built to use a particular library and that library is later updated, you don’t want to have to re-compile that application (and from the end user’s standpoint, you may not have the source). If the updated library uses the same ABI, then your program will not need to change. ABI stability will come with Swift 5.0

Question 24

Why is design pattern very important ?

Answer 24

Design patterns are reusable solutions to common problems in software design. They’re templates designed to help you write code that’s easy to understand and reuse. Most common Cocoa design patterns:
Creational: Singleton.
Structural: Decorator, Adapter, Facade.
Behavioral: Observer, and, Memento

Question 25

What is Singleton Pattern ?

Answer 25

The Singleton design pattern ensures that only one instance exists for a given class and that there’s a global access point to that instance. It usually uses lazy loading to create the single instance when it’s needed the first time.

Question 26

What is Facade Design Pattern?

Answer 26

The Facade design pattern provides a single interface to a complex subsystem. Instead of exposing the user to a set of classes and their APIs, you only expose one simple unified API.

Question 27

What is Decorator Design Pattern?

Answer 27

The Decorator pattern dynamically adds behaviors and responsibilities to an object without modifying its code. It’s an alternative to subclassing where you modify a class’s behavior by wrapping it with another object.

In Objective-C there are two very common implementations of this pattern: Category and Delegation. In Swift there are also two very common implementations of this pattern: Extensions and Delegation.

Question 28

What is Adapter Pattern?

Answer 28

An Adapter allows classes with incompatible interfaces to work together. It wraps itself around an object and exposes a standard interface to interact with that object.

Question 29

What is Observer Pattern?

Answer 29

In the Observer pattern, one object notifies other objects of any state changes.
Cocoa implements the observer pattern in two ways: Notifications and Key-Value Observing (KVO).

Question 30

30- What is Memento Pattern?

Answer 30

In Memento Pattern saves your stuff somewhere. Later on, this externalized state can be restored without violating encapsulation; that is, private data remains private. One of Apple’s specialized implementations of the Memento pattern is Archiving other hand iOS uses the Memento pattern as part of State Restoration.

Question 31

Explain MVC

Answer 31

Models — responsible for the domain data or a data access layer which manipulates the data, think of ‘Person’ or ‘PersonDataProvider’ classes.

Views — responsible for the presentation layer (GUI), for iOS environment think of everything starting with ‘UI’ prefix.

Controller/Presenter/ViewModel — the glue or the mediator between the Model and the View, in general responsible for altering the Model by reacting to the user’s actions performed on the View and updating the View with changes from the Model.

Question 32

Explain MVVM

Answer 32

UIKit independent representation of your View and its state. The View Model invokes changes in the Model and updates itself with the updated Model, and since we have a binding between the View and the View Model, the first is updated accordingly.
Your view model will actually take in your model, and it can format the information that’s going to be displayed on your view.
There is a more known framework called RxSwift. It contains RxCocoa, which are reactive extensions for Cocoa and CocoaTouch.

Question 33

How many different annotations available in Objective-C ?

Answer 33

_Null_unspecified, which bridges to a Swift implicitly unwrapped optional. This is the default.

_Nonnull, the value won’t be nil it bridges to a regular reference.

_Nullable the value can be nil, it bridges to an optional.

_Null_resettable the value can never be nil, when read but you can set it to know to reset it. This is only apply property.

Question 34

What is JSON/PLIST limits ?

Answer 34

We create your objects and then serialized them to disk..

It’s great and very limited use cases.

We can’t obviously use complex queries to filter your results.

It’s very slow.

Each time we need something, we need to either serialize or deserialize it.

it’s not thread-safe.

Question 35

What is SQLite limits ?

Answer 35

We need to define the relations between the tables.

Define the schema of all the tables.

We have to manually write queries to fetch data.

We need to query results and then map those to models.
Queries are very fast.

Question 36

What is Realm benefits ?

Answer 36

An open-source database framework.

Implemented from scratch.

Zero copy object store.

Fast.

Question 37

How many are there APIs for battery-efficient location tracking ?

Answer 37

There are 3 apis.

Significant location changes — the location is delivered approximately every 500 metres (usually up to 1 km)

Region monitoring — track enter/exit events from circular regions with a radius equal to 100m or more. Region monitoring is the most precise API after GPS.

Visit events — monitor place Visit events which are enters/exits from a place (home/office).

Question 38

What is the Swift main advantage ?

Answer 38

To mention some of the main advantages of Swift:

Optional Types, which make applications crash-resistant
Built-in error handling

Closures

Much faster compared to other languages

Type-safe language

Supports pattern matching

Question 39

Explain generics in Swift ?

Answer 39

Generics create code that does not get specific about underlying data types. Don’t catch this article. Generics allow us to know what type it is going to contain. Generics also provides optimization for our code.

Question 40

Explain lazy in Swift ?

Answer 40

An initial value of the lazy stored properties is calculated only when the property is called for the first time. There are situations when the lazy properties come very handy to developers

Question 41

Explain what is defer ?

Answer 41

defer keyword which provides a block of code that will be executed in the case when execution is leaving the current scope

Question 42

How to pass a variable as a reference ?

Answer 42

We need to mention that there are two types of variables: reference and value types. The difference between these two types is that by passing value type, the variable will create a copy of its data, and the reference type variable will just point to the original data in the memory.

Question 43

How to pass data between view controllers?

Answer 43

There are 3 ways to pass data between view controllers.
Segue, in prepareForSegue method (Forward)
Delegate (Backward)
Setting variable directly (Forward)

Question 44

What is Concurrency ?

Answer 44

Concurrency is dividing up the execution paths of your program so that they are possibly running at the same time. The common terminology: process, thread, multithreading, and others. Terminology;

Process, An instance of an executing app
Thread, Path of execution for code

Multithreading, Multiple threads or multiple paths of execution running at the same time.

Concurrency, Execute multiple tasks at the same time in a scalable manner.

Queues, Queues are lightweight data structures that manage objects in the order of First-in, First-out (FIFO).

Synchronous vs Asynchronous tasks

Question 45

Grand Central Dispatch (GCD)

Answer 45

GCD is a library that provides a low-level and object-based API to run tasks concurrently while managing threads behind the scenes. Terminology;

Dispatch Queues, A dispatch queue is responsible for executing a task in the first-in, first-out order.

Serial Dispatch Queue A serial dispatch queue runs tasks one at a time.

Concurrent Dispatch Queue A concurrent dispatch queue runs as many tasks as it can without waiting for the started tasks to finish.

Main Dispatch Queue A globally available serial queue that executes tasks on the application’s main thread.

Question 46

Readers-Writers

Answer 46

Multiple threads reading at the same time while there should be only one thread writing. The solution to the problem is a readers-writers lock which allows concurrent read-only access and an exclusive write access.

Terminology;

Race Condition A race condition occurs when two or more threads can access shared data and they try to change it at the same time.

Deadlock A deadlock occurs when two or sometimes
more tasks wait for the other to finish, and neither ever does.

Readers-Writers problem Multiple threads reading at the same time while there should be only one thread writing.

Readers-writer lock Such a lock allows concurrent read-only access to the shared resource while write operations require exclusive access.

Dispatch Barrier Block Dispatch barrier blocks create a serial-style bottleneck when working with concurrent queues.

Question 47

NSOperation

Answer 47

NSOperation adds a little extra overhead compared to GCD, but we can add dependency among various operations and re-use, cancel or suspend them.

Question 48

NSOperationQueue

Answer 48

It allows a pool of threads to be created and used to execute NSOperations in parallel. Operation queues aren’t part of GCD.

Question 49

NSBlockOperation

Answer 49

allows you to create an NSOperation from one or more closures. NSBlockOperations can have multiple blocks, that run concurrently.

Question 50

KVC

Answer 50

KVC adds stands for Key-Value Coding. It’s a mechanism by which an object’s properties can be accessed using string’s at runtime rather than having to statically know the property names at development time.

Question 51

KVO

Answer 51

stands for Key-Value Observing and allows a controller or class to observe changes to a property value. In KVO, an object can ask to be notified of any changes to a specific property, whenever that property changes value, the observer is automatically notified.

Question 52

Please explain Swift’s pattern matching techniques

Answer 52

Tuple patterns are used to match values of corresponding tuple types.

Type-casting patterns allow you to cast or match types.
Wildcard patterns match and ignore any kind and type of value.

Optional patterns are used to match optional values.
Enumeration case patterns match cases of existing enumeration types.

Expression patterns allow you to compare a given value against a given expression.

Question 53

Explain Guard statement

Answer 53

There are three big benefits to guard statement.

One is avoiding the pyramid of doom, as others have mentioned — lots of annoying if let statements nested inside each other moving further and further to the right.

The second benefit is providing an early exit out of the function using break or using return.

The last benefit, guard statement is another way to safely unwrap optionals.