What is Operator overloading?

Ans : 
Operator overloading is the practice of adding new operators and modifying existing ones to do different things. Operators are those little symbols like +, *, and /, and Swift uses them in a variety of ways depending on context – a string plus another string equals a combined string, for example, whereas an integer plus another integer equals a summed integer.

To create a new operator, try adding this to a playground:

infix operator **

That’s the exponentiation operator, designed to raise one number to the power of another. Normally we’d use the pow() function for that job, but with operator overloading we can make ** work instead.

Now you need to tell Swift what to do when it sees that operator. For example, when we write something like 2 ** 4 what does that mean?

Syntax of making operator : 

func **(lhs: Double, rhs: Double) -> Double {
    return pow(lhs, rhs)
}

Use : 

let result = 2 ** 4

We can specify associativity and a precedence group also but it is very deep level.

If you have any comment, question, or recommendation, feel free to post them in the comment section below!

If there are two views up and bottom, up-view is 60% of superview and 40% of superview respectively, then what to do with constraint?

Ans : 

Use of multiplier in constraint

We took 2 views - Orange and Green. 

We set orange view's top, leading, trailing constraint to main view as 0. 

Same, we set green view's bottom, leading, trailing constraint to main views as 0.

Now,

We select height constraint of orange view equal to main view's height. And set multiplier 0.6. It shows ratio of orange view's height to main view's height. We have set 0.6 = 60/100 . So orange view's height become 60% of main view's height.

Set multiplier of height constraint in size inspector

Same we have done with green view and set multiplier 0.4 = 40/100 means 40%.

If you have any comment, question, or recommendation, feel free to post them in the comment section below!

What is meaning of _ in Swift func ?

Ans : 

The _ is used to define that the parameter is not named

If you have multiple _ it states that you do not need to name the parameters in your function call

func myFunc(name:String, _ age:String){       }

myFunc(“Milo", "I'm a really old wizard")

If you do not use the underscore you would use 

myFunc(“Milo”, age: "I'm a really old wizard")

The _ is not necessary in function calls. It is just used to indicate that something does not to have a name.

Explain application states in iOS

Ans : 

There are 5 application states :

1. Not Running
2. Inactive
3. Active
4. Background
5. Suspended.

Application States

iOS Application Lifecycle : 

When an iOS app is launched the first thing called is

Initialise :

application: willFinishLaunchingWithOptions:-> Bool.
This method is intended for initial application setup. Storyboards have already been loaded at this point but state restoration hasn’t occurred yet.

Launch :

application: didFinishLaunchingWithOptions: -> Bool is called next. This callback method is called when the application has finished launching and restored state and can do final initialisation such as creating UI.

applicationWillEnterForeground: is called after application: didFinishLaunchingWithOptions: or if your app becomes active again after receiving a phone call or other system interruption.

applicationDidBecomeActive: is called after applicationWillEnterForeground: to finish up the transition to the foreground.

Termination :

applicationWillResignActive: is called when the app is about to become inactive (for example, when the phone receives a call or the user hits the Home button).

applicationDidEnterBackground: is called when your app enters a background state after becoming inactive. You have approximately five seconds to run any tasks you need to back things up in case the app gets terminated later or right after that.

applicationWillTerminate: is called when your app is about to be purged from memory. Call any final cleanups here.


Both application: willFinishLaunchingWithOptions: and application: didFinishLaunchingWithOptions: can potentially be launched with options identifying that the app was called to handle a push notification or url or something else. You need to return true if your app can handle the given activity or url.

Above all methods are defined in UIApplicationDelegate and AppDelegate.swift has to implement these methods.

If you have any comment, question, or recommendation, feel free to post them in the comment section below!

What is app group capability in iOS?

Ans : 

If we ever needed to share data between your iOS apps and/or your application targets/extension/widgets , there’s a very easy way to do this using app groups. App group capability introduced with iOS 8.

To do so, we can enable the 'App Group' Capability.

1. In Xcode’s Project Navigator, Click the 'Project Icon'
2. Select the 'Host App' Target
3. Select the 'Capabilities' Tab on the top menu
4. Toggle the 'App Groups' capability
   - If you have not associated a development team you will be prompted to.
5. Select '+' icon and enter a unique group name such as 'group.reverse.company.uri.name'
6. Repeat the above for the Extension’s target

You can then use NSUserDefaults initWithSuiteName:.

NSUserDefaults *sharedDefaults = [[NSUserDefaults alloc] initWithSuiteName:@"group.com.example.app"];

Then set a value in one target…

[sharedDefaults setObject:value forKey:@"key"];
[sharedDefaults synchronize];

And read the associated value in the other target…

NSString *value = [sharedDefaults stringForKey:@"key"];

We can make file observer to be notified for changing value instantly. We can put observer on userdefault.plist file and being notified for some value changed in other application.

Note : BBPortal is example of this.