iOS Interview Preparation Guide

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iOS is a mobile (i phone) operating system developed by Apple Inc. and distributed exclusively for Apple hardware. It is the operating system that powers many of the company's i'Devices.

Speaking of hiding images, if you want to hide one of your own just long tap the image and the Copy/Hide dialog pops up. Tap Hide and the image goes dark to show it has been hidden. You can still find it in the Hidden album, but no one else will see it.

All deleted images are now kept for a period in the 'Recently Deleted' album. That's handy if you ever delete things in error, but be sure to Delete All the images in that album if you happen to be a celebrity trying to keep intimate images from leaking online without your permission.

Repeating message alert sounds getting you down? You can switch it off: Settings>Notifications>Messages Scroll to Repeat Alerts and flip this to Never. Now you will only be alerted once when new messages reach you.

If you have multiple Apple devices that all use your Apple ID you may start to receive calls on all your devices at once. You can control this by switching off iPhone Cellular Calls in the Face-time section of each device's Settings menu, but be sure to only disable this in devices you don't want to use for calls.

If the clicks of your iOS 8 keyboard are driving you mad, switch it off in Settings>Sounds>Keyboard Clicks, toggle to off.

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.

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.

You can switch it off easily: Settings>General>Keyboard and toggle that switch to Off.

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.

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.

On state transitions can be responded to state changes in an appropriate way by calling corresponding methods on app's delegate object.

Signing an application allows the system to identify who signed the application and to verify that the application has not been modified since it was signed. Signing is a requirement for submitting to the App Store (both for iOS and Mac apps). OS X and iOS verify the signature of applications downloaded from the App Store to ensure that they they do not run applications with invalid signatures. This lets users trust that the application was signed by an Apple source and hasn't been modified since it was signed.

The app is in the background but is not executing code. The system moves apps to this state automatically and does not notify them before doing so. While suspended, an app remains in memory but does not execute any code. When a low-memory condition occurs, the system may purge suspended apps without notice to make more space for the foreground app.

The app is in the background and executing code. Most apps enter this state briefly on their way to being suspended. However, an app that requests extra execution time may remain in this state for a period of time. In addition, an app being launched directly into the background enters this state instead of the inactive state. For information about how to execute code while in the background, see "Background Execution and Multitasking.

The app is running in the foreground and is receiving events. This is the normal mode for foreground apps.

The app is running in the foreground but is currently not receiving events. (It may be executing other code though.) An app usually stays in this state only briefly as it transitions to a different state. The only time it stays inactive for any period of time is when the user locks the screen or the system prompts the user to respond to some event, such as an incoming phone call or SMS message.

The app has not been launched or was running but was terminated by the system.

No, the delegate is never retained! Ever!

The frame of a view is the rectangle, expressed as a location (x,y) and size (width,height) relative to the super-view it is contained within. The bounds of a view is the rectangle, expressed as a location (x,y) and size (width,height) relative to its own coordinate system (0,0).

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 auto-release 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.

NSArrayʼs contents can not be modified once itʼs been created whereas a NSMutableArray can be modified as needed, i.e items can be added/removed from it.

A special C data type that encapsulates other pieces of data into a single cohesive unit. Like an object, but built into C.

Fast enumeration is a language feature that allows you to enumerate over the contents of a collection. (Your code will also run faster because the internal implementation reduces message send overhead and increases pipe-lining potential.)

When you build your iOS app, Xcode packages it as a bundle. A bundle is a directory in the file system that groups related resources together in one place. An iOS app bundle contains the app executable file and supporting resource files such as app icons, image files, and localized content.