Difference between Any and AnyObject

ANS : Swift has 2 types for working with  nonspecific type.
1. AnyObject
2. Any

1. AnyObject is for reference type(class) and Any is for both reference and value type.

2. AnyObject represent instance of only any class type, Any represent for any type including function type.

Note : It is always good practice to use specific type instead of Any, AnyObject.

After Swift 3.0, Objective C I'd type can be compatible with Swift Any type. Before that it is equivalent to AnyObject.

I.e

I have created dictionary in which I don't know what will be Value type.

[String : ?? ]

then ?? may be int, float, Array, Dictionary type.

So here we should use Any in replace of ??, because int, float are value type and array, dictionary are class type.

[ String : Any]

What is the nil coalescing operator in swift?

Ans : 

Swift has very powerful in terms of safety because it has feature of optional.

Optional may be has value or may be not. So we try to assign some optional to any another string or any type, then it comes some problem.

Nil Coalescing operator is solution of above problem.

let myname : String = nil
let unwrappedname = myname ?? "Default"

It checks if myname is nill then Default will be assigned to unwrappedname.

So unwrappedname is type of String instead of String?.

Such way nil Coalescing operator ?? is very useful in Swift.

UIViewcontroller Lifecycle

Ans : A view controller manages set of views and making user interface. It will coordinate with data and other controller. Views are automatically loaded when view property is accessed in the app.

Following methods are used to mange view controller's view.

1. LoadView : It is automatically called when it's view property is accessed. It loads or create a view and assigned to property.

2. ViewDidLoad : It is automatically called when view controller completely loaded into memory. Override this method to perform additional initialization on views that were loaded from xib.
I.e instance variable initialization, database access, network request

Event Management to Views :

1. ViewWillAppear : It is called when View is about to added on view hierachy. If we want to change some, then we have to override this method.
Like change orientation, change screen data

2. ViewDidAppear : It is called when view was added on view's hierachy.
When we need to display loader, start UI animation ,then override this method.

3. ViewWillDisAppear : It is called when view is about to removed from hierachy. We can hide keyboard,  commit changes ,revert changes in this method by overriding.

4. ViewDidDisappear : It is called when view is removed from hierachy. We can remove cache data in this method.

Memmory Management method :

1. didReceiveMemoryWarning :
It is called automatically when system determine that the system has low amount of available memory.
Override this method remove not essential data from memory.

Ordering of excecuting methods :

1. Init(coder:)
2. (void)loadView
3. (void)viewDidLoad
4. (void)viewWillAppear
5. (void)viewDidAppear
6. (void)didReceiveMemoryWarning
7. (void)viewWillDisappear
8. (void)viewDidDisappear

What is app thining?

Ans : App thinning automatically detects the user’s device type (i.e. model name) and only downloads relevant content for the specific device. In other words, if you’re using an iPad Mini 1 (which does not have a retina display but rather a 1x resolution), then only your 1x files (more on this in a moment) will be downloaded.  The assets for more powerful and sharper iPads (such as the iPad Mini 3 or 4) will not be available for download).  Because the user needs only download the content that targets his/her specific device, this speeds up the download process and saves space on the device.

There are three aspects of app thining.

1. App Slicing : Slicing is the process of creating and delivering variants of the app bundle for different target devices. App Slicing delivers only relevant assets to each device (depending on screen resolution, architecture, etc.)  In fact, app slicing handles the majority of the app thinning process.
When you’re ready to submit the app, you upload the .IPA or .App file to iTunes Connect, as you typically would (but must use Xcode 7 as it contains the iOS 9 SDK with support for app thinning). The App Store then slices the app, creating specific variants that are distributed to each device depending on its capabilities.

2. On Demand Resources : On demand resources are files that can be downloaded after the app’s first installation.  For example, specific levels of a game (and these levels’ associated content) could be downloaded only when the player has unlocked them.  Further, earlier levels that the player has not engaged with after a certain set time can be removed to save storage on the device.
Enabling on demand resources involves changing the “Enable On Demand Resources” boolean to “Yes” in Xcode settings (under Build Settings).

3.  Bitcode : Bitcode makes apps as fast and efficient as possible on whatever device they’re running.  Bitcode automatically compiles the app for the most recent compiler and optimizes it for specific architectures. Can be turned on by the project settings under Build Settings and selecting bitcode to YES.

App thining process can be test by TestFlight software and install in various device. Size may be vary.

What is size class? Explain with Example.

Ans : 
Size Classes are groups of screen sizes that are applied to the width and height of the device screen. The two Size Classes that exist currently are Compact and Regular.

The Compact Size Class refers to a constrained space. It is denoted in Xcode as wC (Compact width) and hC (Compact height).

The Regular Size Class refers to a non-constrained space. It is denoted in Xcode as wR (Regular width) and hR (Regular height).

iPhone : Most iPhone devices will use the Compact width (wC) size class in each orientation with some exceptions.
The iPhones 6/7 Plus can inherit the Regular width (wR) size class resulting in the ability to use functionality normally reserved for the iPad, such as the split-view pane. Split-VIew pane is speciall made for iPad.

iPad : All iPad devices use the Regular width (wR) size class regardless of landscape or portrait orientation. In both horizontal and vertical landscape, the iPad will use a split-view pane to take advantage of the available screen space because it falls within this unconstrained size class.

Controlling the UI with Size Classes

In most cases, specifying the width class is sufficient when laying out your app; however, you can use the height class to customize your app as well. For example, if you use a split-view pane in an iPad app, users will see the same pane on iPhone Plus in landscape orientation because they both inherit the Regular width (wR) size class.

If that is not your intention, you can exclude a split-view pane from appearing on the 7 Plus by specifying both the width and height Size Classes. This works because the height of an iPhone Plus in landscape orientation is compact (hC) while all iPad devices have a regular height (hR).

You can also use Size Classes to target specific UI elements like font colors, font sizes, drop shadows, view colors and more to adapt to users’ device screen. These variations give you added control as to how your UI can adapt to different devices and orientations that your user may be using.