Which JSON framework is supported by iOS? 

ARC is a compiler-level feature that simplifies the process of managing the lifetimes of Objective-C objects. Instead of you having to remember when to retain or release an object, ARC evaluates the lifetime requirements of your objects and automatically inserts the appropriate method calls at compile time.

ARC is a compiler-level feature that simplifies the process of managing the lifetimes of Objective-C objects. Instead of you having to remember when to retain or release an object, ARC evaluates the lifetime requirements of your objects and automatically inserts the appropriate method calls at compile time.

The presentation of one or more views on a screen is coordinated by UIWindow object..

IOS development requires Intel-based Macintosh computer and iOS SDK

The Singleton design pattern ensures a class only has one instance, and provides a global point of access to it. The class keeps track of its sole instance and ensures that no other instance can be created. Singleton classes are appropriate for situations where it makes sense for a single object to provide access to a global resource.Several Cocoa framework classes are singletons. They includeNSFileManager, NSWorkspace, NSApplication, and, in UIKit,UIApplication. A process is limited to one instance of these classes. When a client asks the class for an instance, it gets a shared instance, which is lazily created upon the first request.

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.

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.

An app can get into InActive state when the user locks the screen or the system prompts the user to respond to some event e.g. SMS message, incoming call etc.