iOS Interview preparation

1. List and explain: IOS application States

Not Running:has not been lanuched or terminated by the system

Inactive:running in foreground and is receiving events stay briefly on their A-to is active.

Active:running in foreground and receiving events.

Background:running in Background and executing code. Stay briefly on their-to is suspended.

Suspended:remains in memory but does execute any code.

2. ios Compiler optimizes references to string objects that has the same value

 nsstring *firstname = @ " jack   " ; NSString  *secondname = @ " jack  Span style= "color: #800000;" > " ;  if  (FirstName == Secondname) {NSLog ( @ " Span style= "color: #800000;" >areequal   );}  else   {NSLog ( @ "  Arenotequal   );}  

FirstName and Secondname is pointers to different objects that has the same value. But the optimization machanism of IOS compiler let both pointers actually pointing to same address.

In Swift, Closures and functions is also assigned by reference. If variable or constant A and B is assigned to the same closure or function, they gonna has exactly the same value in me Mory.

3. Concurrency

==thread:not suggested, hard to design

==dispatch Queues:first in first off only. GCD takes care of creating the needed threads and scheduling tasks to run on those threads.

==operation queue:implemented by Nsoperationqueue don't limited to FIFO order and support complex execution order graphs fo R your tasks.

4.Swift Retain Cycle

1 classA {2 3 Let b:b4 5 init () {6 7b =B ()8 9B.A = SelfTen  One } A  - Deinit () { -  thePrint"A Deinit") -  - } -  + } -  + classB { A  atvar a:a? =Nil -  - Deinit { -  -Print (B deinit") -  in } -  to}

To resolve a retain cycle

When property A and B must isn't be nil, one should is assigned unowned Reference and the other one should be I mplicitly Unwrapped Optional

When one of the property A or B could is nil, the one which can ' t be nil should be assigned unowned.

When both of the property A and B could is nil, assign weak for one property.

5. Objective-c Single Example Singleton

@implementation　　Mymanager+ (ID) sharedmanager {  static Mymanager * staticinstance = nil;　　 static  dispatch_once_t Oncetoken; Dispatch_once (&oncetoken, ^=return  staticinstance;} @end

6. Available prefixs to keyword func in Swift

override: To override methods in superclass you must write override before Func

class: To implement a class method must write class before Func

static: To implement a structures/enumerations method must write static before Func

mutating: For all structures/enumerations methods This could change the instance properties, you must write Mutat ing before func

7. Closures Classification

Global Function:do not capture values

Nested function:capture values from enclosing Function

Closure expression:a unamed Closure that capture values from surrounding context

{(parameters)-(return in statements}

8. Closure Shorthand

Reversed = Names.sort ({(S1:  a href= "" string/a, S2:  a href= "" string/a),  a href= "" bool/a in  R Eturn s1 > s2})

Inferring Type from context

Reversed = Names.sort ({s1, S2 in return s1 > s2})

Implicit Returns from Single-expression Closures

Reversed = Names.sort ({s1, s2 in S1 > s2})

Shorthand Argument Names

Reversed = Names.sort ({$ > $})

Operator Functions

Reversed = Names.sort (>)

iOS Interview preparation