iOS Interview Questions And Answers Part13

1.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.

2.Explain the difference between NSOperationQueue concurrent and non-concurrent. 
Answer:

In the context of an NSOperation object, which runs in an NSOperationQueue, the terms concurrent and non-concurrent do not necessarily refer to the side-by-side execution of threads. 

Instead, a non-concurrent operation is one that executes using the environment that is provided for it while a concurrent operation is responsible for setting up its own execution environment.

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3.Implement your own synthesized methods for the property NSString *title.
Answer:-

Well you would want to implement the getter and setter for the title object. Something like this

- (NSString*) title {
  return title;
}

- (void) setTitle: (NSString*) newTitle {
  if (newTitle != title) 
  title = [newTitle retain]; // Or copy, depending on your needs.
}

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4.Is Objective C support multiple inheritance? How it’s over come?
Answer:-

Objective-C doesn't support multiple inheritance. You could use a protocol, composition and message forwarding to achieve the same result.

A protocol defines a set of methods that an object must implement (it's possible to have optional methods too).

Composition is basically the technique of include a reference to another object and calling that object when it's functionality is required.

Message forwarding is a mechanism that allows objects to pass messages onto other objects, for example, an object that is included via composition.

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5.Explain Application lifecycle
Answer:

Chronology of an application: 

When the process is started, it runs the NSApplicationMain function, which creates an instance of NSApplication.

The application object reads the main nib file and unarchives the objects inside. The objects are all sent the message awakeFromNib.

Then the application object checks for events.

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