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iOS interview questions

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Use our complementary questions and answers to filter and hire the best. Questions crowdsourced by our clients, answers by Punch. We provide these complementary questions to help our clients more quickly create tests for potential hires at their organizations.

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Question
What framework is used to build an iOS app’s user interface, and what does it provide?
Answer
The UIKit framework is used to develop application’s user interface. UIKit framework provides event handling, drawing model, windows, views, and controls, specifically designed for a touch screen interface. The UIKit framework (UIKit.framework) provides the crucial infrastructure needed to construct and manage iOS apps.
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Question
What would we say the state of an app is, if it’s loaded into memory but is not executing any code?
Answer
An app is said to be in Suspended state when it is still in memory but is not executing any code.
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Question
Which is the super class of all view controller objects?
Answer
All view controller objects inherit from a UIViewController class which provides functionality for loading views, presenting them, rotating them in response to device rotations, and several other standard system behaviours.
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Question
What is an App Bundle?
Answer
Just like a directory in a file system that groups related resources together in one place, an iOS app bundle contains the application’s executable file and supporting resources such as app icons, image files, and localised content. The application is packaged in a bundle by Xcode when it is compiled.
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Question
Outline the class hierarchy for a UIButton until NSObject.
Answer
UIButton inherits from UIControl. UIControl inherits from UIView. UIView inherits from UIResponder. UIResponder inherits from the root class NSObject.
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Question
What is the difference between Delegate and KVO?
Answer
Both are ways to have relationships between objects. Delegation is a one to one relationship where one object implements a delegate protocol and another uses it and sends messages to assuming that those methods are implemented since the receiver promised to comply to the protocol. KVO is many-to-many relationship where one object could broadcast a message and one or multiple other objects can listen to it and react.
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Question
Where wouldn't you use singletons and where you wouldn't?
Answer
Singletons should be avoided and used only for objects that need to be shared throughout your application. It should be used carefully, instantiated lazily, if it’s possible, and passed into other objects as a dependency using Inversion of Control and Dependency Injection principles.
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