Objective C Interview Questions

The Objective C programming language is a simple computer language that allows for complex object-oriented programming. Objective C is a modest but strong set of extensions to the mainstream ANSI C programming language. Smalltalk, one of the first object-oriented programming languages, is at the heart of its additions to C. Objective C is intended to provide full object-oriented programming features to C in a clear and basic manner.

1. Jump to

   What is Objective C?

Objective-C, an ANSI-based variant of the conventional C programming language, is the primary programming language used by companies that create apps for OS X and iOS. Objective-C is built on top of the C language, with Small Talk features added to make it an object-based language.

2. How to make a static method?

Methods are always implemented as static functions in Objective-C. Because the function itself is tied to the file that implements the method, the only way to retrieve the IMP (implementation pointer) of a method is at the runtime (through method: and friends).

3. What is the difference between #import and #include in Objective-C?

Import is a superset of include; it ensures that a file is only included once. This prevents recursive inclusion. about “” and <>. “” searches the local directory, while > searches for system files.

4. What is the use of category in Objective-C?

A category is often used to add methods to an existing class, such as one specified in the Cocoa framework. Subclasses inherit the new methods, which are indistinguishable from the class’s original methods at runtime. You can also use your class categories to: Distribute the implementation of your classes into distinct source files — for example, you might divide a huge class’s methods into numerous categories and place each category in a separate file. Create private methods.

5. Explain class definition in Objective-C?

A class definition begins with the keyword @interface, is followed by the name of the interface (class), and is closed with a pair of curly brackets.  All classes in Objective-C are fetched from the foundation class called NSObject. It provides fundamental methods such as memory allocation and initialization.

6. Explain what is @synthesize in Objective-C?

@synthesize provides a variable getter and setter. This allows you to provide some properties for your variables, and when you @synthesize that property to the variable, the getter and setter for the variable are generated.

7. Explain the difference between atomic and nonatomic synthesized properties.

Atomic is the default behavior, which ensures that the current process is completed by the CPU before another process accesses the variable. This is not quick behavior because it ensures that the process is completed completely.

Non-Atomic is NOT the default behavior quicker (for synthesized code, that is, variables generated with @property and @synthesize) not thread-safe may result in unexpected behavior when two separate processes access the same variable at the same time.

8. How do you manage memory in Objective C?

Memory allocation is done dynamically in Objective C. This means that memory gets allocated during the course of any program’s execution. It is being used, and then it is released when it is no longer needed. This contributes to using as little RAM as possible. Throughout the memory lifetime, things use as much memory as they require and then release it when it is no longer required. There are two methods for allocating memory in Objective C:

• Manual Retain Release (MRR):
• Memory is explicitly managed under this sort of memory management, and all objects are tracked. It keeps track of this using the reference counting model.
• Automatic Reference Counting (ARC): The runtime is where the system can insert relevant memory management method calls.

Memory management has two major drawbacks: when it is over free, it causes repeated system crashes, and when it is not freeing, it creates memory leaks, which increases the application’s in-memory footprint.

9. What is the responder chain?

The responder chain is a collection of responder items that are linked together. It goes from the first responder to the app object. If the first responder is unable to handle an event, the incident is forwarded to the next responder in the responder chain.

10. Are id and instanceType same? If not, what are the differences between them?

Replace occurrences of id as a return value with instancetype in your code as needed. This is common for init methods and class factory methods. The compiler changes methods that begin with “alloc,” “init,” or “new” and have a return type of id to return instancetype automatically, but it does not convert other methods. For all methods, the Objective-C convention is to write instance type explicitly.

11. What is a delegate? Can delegates be retained?

When an object encounters an event in a programme, a delegate acts on its behalf or in conjunction with another object.It is all up to you. It will be retained if you indicate it to be retained (strong in ARC). The rule is to not keep it because it has already been retained somewhere, and by doing so, you will avoid retain cycles.

12. What is class extension? Why do we require them?

Through categories and class extensions, Objective-C allows you to add your own methods to existing classes.

Class Extends the Internal Implementation.

A class extension is similar to a category, except it can only be added to a class for which you know the source code at build time (the class and the class extension are both compiled). The methods declared by a class extension are implemented in the original class’s @implementation block, therefore you can’t declare a class extension on a framework class, such as a Cocoa or Cocoa Touch class like NSString.

13. What are objective- C blocks?

There is an object in the Objective-C class that combines data with relevant behaviour. It allows you to create discrete sections of code that may be passed around to functions or methods like values. Collections such as NSDictionary and NSArray can be enhanced with Objective-C blocks.

14. How does messaging work in Objective-C?

In Objective-C, messaging is not tied to method implementation until runtime. A message expression is converted by the compiler into a call to the messaging function objc_msgSend().  This function links the recipient and the method name mentioned in the message.

15. When do we use NSArray and NSMutableArray?

When the data in the array is not going to change, it is best to utilize NSArray. For example, if a company’s name is likely to change frequently, NS Array can be used to ensure that no one tampers with it.

Unlike NS Array, this array is utilized when the data in an array changes often. A function with values passed to the array as a function can be considered here, and this function will append some elements to that array. An NSMutable array can be used at this moment.

16. What are the methods of using the NSURL connection?

The methods that can be used in NSURL connection are the following connections:

• A connection that received the response
• A connection that receives data
• A connection that fails with an error
• A Connection that did finish loading

17. How does dispatch_once manage to run only once?

Dispatcher_once() is a synchronous process, whereas other GCD methods operate asynchronously (except dispatch_sync(), which is synchronous).

The whole point of dispatch_once() is to “do something once and only once,” which is exactly what we’re doing. dispatch_once is used to ensure that anything only happens once, regardless of how vicious the program’s threading becomes.

18. How can we put nil into a dictionary/array?

The nil in initWithObjects: is only there to tell the method where the list ends, because of how C var args work. When you add objects one by one with addObject: you don’t need to add nil.

19. What are some of the advantages of using a session?

There are numerous advantages of making use of a session as mentioned below:

• It is used to store user data across the span of an application.
• It is very easy to implement and store any sort of object in the program.
• Individual entities of user data can be stored separately if required.
• The session is secure, and objects get stored on the runtime server.

20. What is dot notation?

Dot notation is used to evaluate an instance variable by first determining the class “instance” followed by a “dot” followed by the name of the instance variable or property to be accessed.

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