Objective C Interview Questions and Answers

Objective C Interview Questions and Answers

Objective C Interview Questions and Answers

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Best  Objective C Interview Questions and Answers

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Q1) Explain what is basically Objective C?

Answer: The primary programming language that is used to build and develop mobile smartphone applications is known as Objective C. This is used both in Android and IOS technologies.

Q2) Who were the inventors of Objective C?

Answer: The inventors of Objective C were Tom Love and Brad Cox.

Q3) When was this invented?

Answer: Objective C was invented in the 1980s.

Q4) What was the name of their company?

Answer: The name of the company where Objective C was invented was known as Stepstone.

Q5) State the latest version of Objective C.

Answer: The most upgraded version of Objective C was launched by the company Apple … Objective C 2.0

Q6) In which year was the latest version of Objective C released?

Answer: The year in which the latest version of Objective C was discovered was 2006.

Q7) In which tech conference was the latest version launched?

Answer: It was launched at the Worldwide Developers Conference.

Q8) State the two types of protocols it encompasses.

Answer: The two different types of protocols Objective C encompasses are … formal and informal.

Q9) What are the categories used for?

Answer: In order to add methods to an already existing class, a category is needed. Categories are also used to disseminate implementing their respective classes into individual source files.

Q10) What is the key difference between NSArray and NSMutableArray?

Answer: Static arrays are created by the former and the creation of dynamic arrays is by the latter.

Q11) What property does @synthesize achieve?

Answer: When a developer needs to specify attributes or characteristics to certain variables, one uses @synthesize. This also helps generate better and more setter for the variables involved.

Q12) What kind of class is NSObject?

Answer: This is the root class. A lot of other classes stem from this. NSObject defines the basic behavior patterns for object interactions.

Q13) State the key difference between atomic and non-atomic synthesized properties.

Answer: The former is the default set behavior pattern. The latter is not the default behavior and the consequences of the same might be potentially unexpected.

Q14) State the full form of GCD.

Answer: The full form of GCD is Grand Central Dispatch.

Q15) What is the function of GCD?

Answer: The main advantage of creating a GCD is that only one thread is developed to execute the blocks and the execution of the same happens sequentially. Hence there is nothing unexpected to preempt.

Q16) State the full forms of KVC and KVO?

Answer: The full form of KVC is Key-Value Coding and the full form of KVO is Key-Value Observing.

Q17) What are the properties of Key-Value Coding and Key-Value Observing?

Answer: The main advantage of Key-Value Coding is that it allows accessing any value using a string. When programmers need to decipher a change or a modification in their properties they use Key-Value Observing as it allows them to do so.

Q18) What do you understand by blocks?

Answer: Blocks is the name given to language level features.

Q19) How are blocks used?

Answer: Blocks are used to create code segments that are cascaded to functions to be utilized as values. The caret symbol is the syntax that is used to define a block.

Q20) What do you understand by the responder chain?

Answer: A sequential series of responder objects that are linked together are known as a responder chain. In this case also, if the first responder is unable to execute the command, it is passed onto the next in line and so on and so forth till it reaches the last responder in the chain.

Q21) State some advantages of utilizing Objective C.

Answer: Some advantages of utilizing Objective C are as follows… it has documented frameworks, it has strong online support, it is a stable language, it works smoothly with C and C++ and it is a time tested and mature language.

Q22) What do you understand by id?

Answer: A pointer to any type is called id.

Q23) Is there a possibility of function overloading in Objective C?

Answer: No there is no possibility of function overloading in Objective C.

Q24) What do you understand by a delegate?

Answer: A delegate is an object that co-coordinates for or on behalf of other objects during a program run.

Q25) Can delegates be retained? Is it advisable to do so?

Answer: Yes, delegates can be retained. However, it is not considered advisable to do so.

Q26) Why does dispatch_once run only once?

Answer: Dispatch_once is an asynchronous process. Hence it can perform one task only once. It is not built for multitasking purposes.

Q27) State the methods in which memory is allocated in Objective C.

Answer: Memory is allocated in two ways in Objective C. They are … manual retail release (MRR) and automatic reference counting (ARC).

Q28) What are some of the attributes of properties in Objective C?

Answer: Some of the attributes of properties in Objective C are as follows…copy, retain, assign, re-write and read-only.

Q29) Can ARC and Non-ARC codes be used together in projects?

Answer: Yes, they can be used together as well.

Q30) State some of the methods for using NSURL connections.

Answer: Some of the methods for using NSURL connections are as follows…when the connection receives the response, when the connection receives the data, when a connection fails and shows the error and when the connection finishes loading.

Q31) What works only for instance variable?

Answer: It is Dot notation which only functions on the instance variables that are connected with the controller methods are to be announced. If you try to connect for using dot notation for connecting instance variable for not combining the controllers in the code will decline to organize with an issue. It is also used to place the principles of property details. Dot notation requires to gain the instance variable by stating the class instance by the dot.

Q32) Define Protocols?

Answer: It is a set of properties and methods is applied by class. Protocols are adaptable and can repeat a single API announcement in finishing the class which is not connected. For presenting a parallel connection on the top of a live class hierarchy. This is a small model protect the basics of working with the protocols.

Q33) Explain Retain count?

Answer: The strategy is applied by the mention counting. The retain method takes the retain count. Every single item contains a retain count, at the time when an item generates the default count as 1. When the fresh item is generated and goes like a retain message then the count is increased in 1. The count decreases in 1 at the time of an item sends like the discharge message. The time when an item sends a tireless message then the count reduces.

Q34) Define Cocoa?

Answer: Cocoa is known as an application environment and a collection of object-oriented components. It helps in generating the application of OSX and iOS. The application is generated by applying an Objective C language. It is based out of ANSI C code is combined with Objective Code at the time of constructing a Cocoa Application.

Q35) Define Category in Objective C?

Answer: If you wish to expand the actual class by computing the behavior which is convenient in a particular condition. To compute the development for actual classes, objective C delivers categories and extension. If requires to compute a method to the actual class, then compute performance to make easy for performing anything is a very convenient way to utilize a category. The syntax for announcing a category utilizes the @interface keyword. It is like a standard Objective C class but does not express any estate of the subclass. It defines the name of a category.

Q36) Explain the message passing in Objective-C?

Answer: Passing a message is an expression of requesting methods on the objects. To deliver or pass an argument is known as a message For example Considering setStr and setX are the methods for the SomeClass object and Ptr is a pointer od detail of the SomeClass. This is the way to join the receiver and the name of the method is viewed in the message.

Q37) How to assure a valid value to return?

Answer: With the help of Atomic property, keep in mind that always a valid value is not to be right. Various thread is used to write and read at the same time. Atomic properties are not safe thread. Minor properties tolerate forming the small activities by securing ad un securing before and after setting and receiving value. And known as the default character for the properties.

Q38) Who does not assure the return value?

Answer: Non-Atomic properties, it may be the accurate value, moderately written value or any garbage value. But it is not threaded safe for all but only for improving the speed of connecting the properties. It has no surety for the returned value.

Q39) How to store Data with NSUserDefaults in objective C?

Answer: NSUserDefaults is an easy property group to save an application the simple data. To save default settings, preference or default values in or in shape. Save the data including the few lines of code to load the data quickly. To store fewer data without any difficult operation is needed. The main thread is not blocked for making UI operations faster and for the application to run smoothly.

Q40) How to hold a list of objects in a system?

Answer: With the help of object-oriented programming to organize the programs around the data. An item is explained as the data has a special connection and behavior. An item can scope from the material entities like a person is defined by the properties such as name and address, down to small programs of the computer. To recognize each object in a program, we need to operate and relate with each other. After knowing the object, it is created as the class of the items to define the variety of data and order of argumentation to operate. Every defined argument is considered as method and items are for interaction with a described estate is a message.

Q41) What is Encapsulation?

Answer: The applied and condition of every item are securely managed inside the boundary or class. Other objects do not contain the connection in the class of the power for converting. They can call a group of public functions or methods. The feature od data hiding delivers great program security and escapes unexpected data corruption.

Q42)  What are synthesized Accessor methods?

Answer: It is the method that exists in a class to permit the programmer to have and set the principles of the instance variable included in the class. The accessor method is to get and set the bank account details and balance variables. To write the methods on a huge number of difficult classes will surely take too much time. Objective C delivers a mechanism to automatize the generation of accessor methods.

Q43) Define functions in Objective C?

Answer: It is known as the list of the statements together for executing a task. Objective c program contains at least one C function that is main (). The announcement of function informs the compiler about the name, return type, and parameter of the function. But in Objective c the function is called the method.

Q44) Describe calling a method?

Answer: At the time of generating an objective C method, so provide the details to function, what do to. With the help of a method call the function to execute the described projects. The power of the program moves to the called method. A called method executes the described project when it reverts the declaration is performed and then it reverts the power of the program to the main program. For calling a method, we need parameters besides the name. when the method reverts a value than you can save the returned value.

Q45) Define the function of Arguments?

Answer: If the function uses the disagreement, then announce the variables in which the principles of the arguments are called formal parameters of the function. The formal parameters perform as another local variable in the function and they are generated in a record in the function and consume on exit.

Q46) Name the method to pass an argument for copying the address?

Answer: In the formal parameter, the call by reference is the way to deliver the arguments to a function for copying the address of an argument. In the function, the address is utilized to connect the real argument which is utilized in a call. The modification for the parameter influences the passed arguments. For moving the principle by references, argument pointers are moves to the function as another principle. And you have to announce the function parameter like the pointer types in the swap() function .it is to convert the principles of two integer variables from the arguments.

Q47) Name the method to copy the actual value?

Answer: By the method call by value, it moves the disagreement to the function copies the real value of an argument in the formal parameter. The modification of the parameter in the function does not put an influence on the argument. By default, Objective, C utilizes call by value way to move the disagreements. The code in the function cannot change the disagreements for calling the function.

Q48) Define constants in objective C?

Answer: Constants are used to affix the principles so the program should not change at the time of implementation. Constants are the fundamentals of data type such as numeric, character unsettled constant but also catalog contents. The constants are known as structured variables. But the principles are not changeable once it is described.

Q49) What is considered in a decimal form?

Answer: A floating-point literal, it is a part of an integer, a decimal point, and a fractional and exponent part. At the time when we use a decimal form, then it contains the decimal point and exponent or both together. And utilizing the exponential form, then it contains the integer part, the fractional part or both together.

Q50) Explain Boolean to avoid the bugs in Objective-c?

Answer: It manages the data type from the language C. Zero is considered as false and 1 is considered as true in objective C. Boolean data type is in C to provide the principle of True and False. Objective-c delivers the various versions of the same type which is written in Bool and grabs the macro of Yes or No. In objective –c Bool is a typedef and signed char.

Q51) Name the principle of Loop?


  • Abstraction – The object discloses the inner machine which is suitable for utilizing another object, covering the unimportant code.
  • Encapsulation – The execution and condition of each item are held very securely.
  • Inheritance – The communication and subclasses in the middle of items are allowed when the developers restate an ordinary logic for managing a supreme hierarchy.
  • Polymorphism – Objects have permission to have many forms on the content. The programs decide the meaning and the use for every implementation of the item.

Q52) What is meant by Suspended?

Answer: The application is hidden but it not performing code. The system transfers the application to a special condition as a result and it not able to inform them before. The application remains in memory but did not accomplish any code. If a low memory state occurs, the framework will clean the application of suspended for including a lot of space for the front application.

Q53) Name the characteristics of category in Objective C?


  • A category may announce whether you do not contain the real source code for applying.
  • The methods which you have described in a category are available for all details of the real class but also the sub-classes for the real class.
  • No variation is found between a method attach by the category at the time of runtime. And one of them is applied by the original class.

Q54) What is the Implementation file?

Answer: The implementation of the class contains in the file main.m in the exploration sidebar. We require to add the #import” main.h” preprocessing statement in the class for finishing the BMI class. We have to generate a class each time for importing the gathered file in the performance file. To announce the gathering, you need to announce the perforation with the use of the @implementation directive displaced by the class name is BMI.

Q55) What is pointer to pointer in objective c?

Answer: It is considering as a group of pointers that includes the locations of the variable. At the time of describing the pointer then the primary pointer includes the location of the second pointer. That indicates the address which includes the real value.

Q56) Define interface?

Answer: In objective C each new class id announces with the help of @interface displaced by the custom class name. And it is displaced by the colon and end with a subclass name. Every class is copied by the NSObject from the base class. And known as the superclass for every objective-c classes. The @interface line and @end line describes the thing class contains.

Q57) Describe the properties in Objective –C?

Answer: In objective –c properties are described as to assure the instance variable of the class which penetrates out of the class. Getter and setter methods are generated for the properties.

  • Properties start with @property and are known as a keyword.
  • It is displaced with atomic connection, monatomic read-write, read-only, strong or weak. It is based on the type of variable. We use strong or weak for the pointer type. And use read-write or read-only for others.
  • The name of the property is canceled by the semicolon.
  • In the implementation, the class attaches the statement of synthesizing. In the advance Xcode, the synthesis is protected by Xcode and not to add synthesize a statement.

Q58) How to import objective c into Swift?

Answer: Objective-c and Swift files are used both together in a single project with any language. It is possible to make a mixture of language application and framework focus on generating an application or framework which contains a single language. The procedure for using the objective c announcement from the swift code in a mixture of language focus different kind of for writing an application or framework.

Q59) How to import code within the App target?

Answer: To construct a group of objective –c file in the swift code containing a similar app target. Build on an objective-c spanning header file for disclosing the file t Swift. Xcode allows to generate the file at the time of attaching a Swift file to a live objective c application after accepting Xcode generates the span header file with the file have generated easier to name it by the product module name.

Q60) How to import cade with the framework target?

Answer: Utilizing the objective-c announcement in the files in a similar framework target as the Swift code. Then requires constructing the files in the objective –c for umbrella header and the framework the header master. Each header is viewed in the umbrella header by the Swift. Import each objective c header to displace in the umbrella header.

Q61) Steps to attach objective-c files in a Swift Cocoa touch framework?


  • First, please attach the objective files in the projects that may be drag or drop.
  • Then keep the files inside the project
  • now go in the “Project Target” then “Build phase”
  • Then on “headers”
  • View all “h” files in the “project” option
  • Finally, import in the Bridge file (is generated by the Xcode)

Q62) How to generate an objective –c bridging header to utilize code in Swift?

Answer: For generating an objective –c spanning header file then drag objective-c code inside the Swift project=Xcode will cause with the message For example- if you wish to configure an objective-c spanning header then click on “Creating Bridging Header” now view the file “YourProjectName-Bridging-Header.h occurs in the project.

Q63) Steps for attaching drag and drop in the App?

Answer: First, In the Xcode generate a new single view template

Now open to editing open ViewController.swift

  • Then keep two table view infilled with example data
  • Generate two table view
  • Then generate 2 string array filled with left and right
  • Configure table view for utilizing the view controller as the data source.

Q64) How to create the custom subclasses of NSO?


  • First, generate a fresh file
  • Select the “Cocoa Touch Class”
  • Then click on Next and the name of “person”
  • Now type “NSObject” for” Subclass of”
  • Then hit on “Next”
  • And then click on “create” for creating a new file.

NSObject is known as the universal base class for all the Cocoa Touch classes. Every class of UIKit arrives from NSObject.

Q65) What is a calling method on Nil pointer?

Answer: In Objective c, the mail which is dispatched to a Nil object is allowable in objective c like a no-op. We cannot identify an issue because it is not considered as an issue. If you wish to deliver a calling method and your object pointer is Nil, then your arrival value is like return type.

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