面试题与答案

iOS stands for "iPhone Operating System".

It is the operating system for Apple devices, and it is considered the second most popular mobile operating system globally after Android.

This operating system powers many of Apple's products including the iPhone, iPad, and iPod. iOS is widely praised for its intuitive and user-friendly interface.

• The iPhone offers multitasking capabilities. On an iOS device, you can easily switch between apps using the multitasking feature or a multi-finger gesture.
• iOS helps you easily integrate social network interactions with your app by displaying an activity stream and sharing content.
• Apple's iCloud service allows users to store data on the Internet. It offers a high level of encryption and a backup option to ensure the user does not lose data.
• Apple's in-app purchases are available on all platforms, offering users additional services and materials including digital items (iOS, iPad, macOS), subscriptions, and premium content.
• You can see all of your app alerts in the Notification Center in iOS. However, the notification settings can be modified.
• iOS is a closed system. The source code of Apple's apps isn't available for developers, and iPhone and iPad owners can't modify the code on their devices. This makes iOS-powered devices harder to hack.

iOS operates in a Layered structure.

iOS Architecture is comprised of four layers, each of which offers a programming framework for creating applications that operate on top of the hardware. Communication will be enhanced by the layers between the Application Layer and the Hardware Layer. A lower-level layer provides the services that all applications require, while an upper-level layer (or high-level layer) provides graphics and interface-related services.

Properties are basically values that are associated with a class, struct, or enum.  They can be thought of as "sub-variables," i.e., parts of another object.

Example:

struct Building  {    

    var name: String = ""

}

var apartment = Building()

apartment.name = "Prestige"

In the above code, we created a structure called Building. One of its properties is called name, a String whose initial value is empty. 

Stored Properties: This type of property can be used to store constant or variable values as instances and is usually provided by classes and structures.

class Programmer {    

    var progName: String    

    let progLanguage: String    

    var totalExperience = 0    

    var secondLanguage: String?

}

Computed properties: These properties can be used to calculate values instead of storing them and are usually provided by classes, enumerations, and structures.

struct Angle {    

    var degrees: Double = 0    

    var rads: Double {        

        get {            

             return degrees * .pi / 180        

        }        

        set(newRads) {            

              degrees = newRads * 180 / .pi        

        }    

    }

}

Atomic Property: It is the default property and ensures a valid value will be returned from the getter or set by the setter. This ensures that only one thread can access the getter/setter of a given property at a time and that all other threads must wait until the first thread releases the getter/setter. Despite being thread-safe, it is not fast, since it ensures that the process is completely completed.

Non-Atomic Property: With non-atomic properties, multiple threads can access the getter/setter method of a given property at the same time, so the potential for inconsistency between values exists. They come with enhanced access, but no guarantee of the return value.

Android: It is the mobile operating system for Android devices offered by Google LLC (limited liability company) and is focused on touchscreen mobile devices like smartphones and tablets. Several programming languages were used in its development, including C, Java, C++, and others. 

iOS: It is the operating system for Apple devices offered by Apple incorporation and it is considered the second most popular mobile operating system globally after Android. It is primarily designed for Apple mobile devices like the iPhone, iPod Touch, etc. Several programming languages were used in its development, including Objective-C, Swift, C++, and others. 

For more differences, please check here.

Programming languages used for iOS development are:

• HTML5
• .NET
• C
• Swift
• Javascript
• Objective-C

Objects are mainly the variables that are of class types. It can be a function, method, data structure, or variable.

UIKIT framework. It renders drawing models, windows, event handling, and views.

 It is used to add a set of related methods and to add additional methods in the Cocoa framework.

The process of adding new operators and changing existing ones to do various things is known as operator overloading.

+, *, and / symbols are known as operators.

The visual elements that we can see in our applications are known as UI elements. Some of these components, such as buttons and text fields, respond to user interactions, while others, such as images and labels, provide information.

Objective-C is the primary programming language for writing applications for OS X and iOS. It’s an object-oriented programming language with a dynamic runtime that’s a superset of the C programming language. Objective-C takes C’s syntax, primitive types, and flow control statements and adds class and process definition syntax.

NSObject -> UIResponder -> UIView -> UIControl -> UIButton. 

MVC (Model View Controller) is a design pattern that defines how logic will be separated when the user interface is implemented. In iOS, UIView is the base class provided by Apple for all views, and UIViewController is provided to support the Controller, which listens to events in a View and updates it when data changes.