Sunday, March 29, 2015

iPhone Interview Questions with answers

Q.iOS Architecture

Q.iOSApp lifecycle

Q. Where can you test Apple iPhone apps if you don’t have the device?
A.  iOS Simulator can be used to test mobile applications. Xcode tool that comes along with iOS SDK includes Xcode IDE as well as the iOS Simulator. Xcode also includes all required tools and frameworks for building iOS apps.  However, it is strongly recommended to test the app on the real device before publishing it.

Q. Does iOS support multitasking?
A.  iOS 4 and above supports multi-tasking and allows apps to remain in the background until they are launched again or until they are terminated.  

Q. What are the tools required to develop iOS applications?
 A. iOS development requires Intel-based Macintosh computer and iOS SDK. Current Mac os version is 10.11, Xcode version 7.1.1 iOS Version 9.1

Q. Name the framework that is used to construct application’s user interface for iOS.
 A. The UIKit framework is used to develop application’s user interface for iOS. UIKit framework provides event handling, drawing model, windows, views, and controls specifically designed for a touch screen interface.

Q. Name the application thread from where UIKit classes should be used? 
A.  UIKit classes should be used only from an application’s main thread.  
Note: The derived classes of UIResponder and the classes which manipulate application’s user interface should be used from application’s main thread. 

Q. Why an app on iOS device behaves differently when running in foreground than in background? 
A. An application behaves differently when running in foreground than in background because of the limitation of resources on iOS devices.

Q. How can an operating system improve battery life while running an app?
 A. An app is notified whenever the operating system moves the apps between foreground and background.  The operating system improves battery life while it bounds what your app can do in the background. This also improves the user experience with foreground app.

Q. When an app is said to be in active state?
 A. An app is said to be in active state when it is running in foreground and is receiving events.

Q. An app is loaded into memory but is not executing any code. In which state will it be in?
 A. An app is said to be in suspended state when it is still in memory but is not executing any code.

Q. How can you respond to state transitions on your app? 
A. On state transitions can be responded to state changes in an appropriate way by calling corresponding methods on app's delegate object.
For example: applicationDidBecomeActive method can be used to prepare to run as the foreground app.
applicationDidEnterBackground method can be used to execute some code when app is running in the background and may be suspended at any time.
applicationWillEnterForeground method can be used to execute some code when your app is moving out of the background
applicationWillTerminate method is called when your app is being terminated.

Q. List down app's state transitions when it gets launched.
 A. Before the launch of an app, it is said to be in not running state.
When an app is launched, it moves to the active or background state, after transitioning briefly through the inactive state.

Q. Who calls the main function of you app during the app launch cycle? 
A. During app launching, the system creates a main thread for the app and calls the app’s main function on that main thread. The Xcode project's default main function hands over control to the UIKit framework, which takes care of initializing the app before it is run.

Q. What is the use of controller object UIApplication?
A. Controller object UIApplication is used without subclassing to manage the application event loop.
It coordinates other high-level app behaviors.
It works along with the app delegate object which contains app-level logic.

Q. Which object is create by UIApplicationMain function at app launch time?
A. The app delegate object is created by UIApplicationMain function at app launch time. The app delegate object's main job is to handle state transitions within the app.

Q. How is the app delegate is declared by Xcode project templates?
A. App delegate is declared as a subclass of UIResponder by Xcode project templates.

Q. What happens if IApplication object does not handle an event?
A. In such case the event will be dispatched to your app delegate for processing.

Q. Which app specific objects store the app's content?
A. Data model objects are app specific objects and store app’s content. Apps can also use document objects to manage some or all of their data model objects.

Q. Are document objects required for an application? What does they offer?
A. Document objects are not required but are very useful in grouping data that belongs in a single file or file package.

Q. Which object manage the presentation of app's content on the screen?
A. View controller objects takes care of the presentation of app's content on the screen. A view controller is used to manage a single view along with the collection of subviews. It makes its views visible by installing them in the app’s window.

Q. Which is the super class of all view controller objects?
A. UIViewController class. The functionality for loading views, presenting them, rotating them in response to device rotations, and several other standard system behaviors are provided by UIViewController class.

Q. How do you change the content of your app in order to change the views displayed in the corresponding window?
A. To change the content of your app, you use a view controller to change the views displayed in the corresponding window. Remember, window itself is never replaced.

Q. Define view object.
A. Views along with controls are used to provide visual representation of the app content. View is an object that draws content in a designated rectangular area and it responds to events within that area.

Q. What are layer objects and what do they represent?
A. Layer objects are data objects which represent visual content. Layer objects are used by views to render their content. Custom layer objects can also be added to the interface to implement complex animations and other types of sophisticated visual effects.

Q. Difference between Static & Dynamic TableView
Static cells are basically a "what you see is what you get" in Interface Builder. What you put into theUITableView is what you'll see when you run the app.
Dynamic prototypes, instead, allow you to lay out cells that you can re-use by calling:
UITableViewCell * cell = [tableView dequeueReusableCellWithIdentifier:CELL_ID_SET_IN_IB];
With this, you determine the number of cells using the delegate methods in the UITableViewController. You can have multiple prototype cells and determine which to load depending on index path.

we can use segues with both.
Q. What is NSUserDefaults? What type of data can we store there?
NSUserDefaults is a simple property list (aka plist) where an app can store simple data. While there is no limit to its size (besides the device’s own limits), you should not store a large amount of data here. The file is written and read atomically (as a whole), so the more data that is in there, the longer that will take
Q. What is the output binary format?
.ipa file
iOS Enterprise Program - Can distribute apps only within enterprise not to App Store. No limit on number of devices you can distribute your apps to. Can restrict access where member can request developer certificate, admins approve it. Cannot distribute apps via AppStore.
iOS Developer Program - Can test the apps on max 100 devices only. Distribute apps to AppStore.

Q. Explain retain counts.

Retain counts are the way in which memory is managed in Objective-C. When you create an object, it has a retain count of 1. When you send an object a retain message, its retain count is incremented by 1. When you send an object a release message, its retain count is decremented by 1. When you send an object a autorelease message, its retain count is decremented by 1 at some stage in the future. If an objectʼs retain count is reduced to 0, it is deallocated.