Swift Protocol and Implementation

-
Protocols in Swift , define requirements that has to be implemented by a Class adopting or conforming to it.

Protocols can be adopted by a Class , Structure or Enumeration , all of which can actually implement them based on the requirements. But, in one scenario you can't adopt protocol for Structure and Enumeration. Please go through the entire article for further understanding.


Lets consider a simple example with Inheritance and Requirement (Protocol defines Requirements).


Object Inheritance.
Department Object is inherited by Administration , Finance and Human Resource Department. So all the departments will have inherited properties like departmentName and departmentId.

 Protocol.
Protocol define the requirements. These requirements can be required or optional. requirements If you notice in the design listed below, you will notice two type's for requirements.

1) Required 

func dressCode(departmentType: Int) -> UIColor

func numberOfEmployees() -> Int 

2) Optional 

func employeesInRange(fromDate: Date, toDate: Date) -> Int






Department.swift
import Foundation

class Department:NSObject {
    var departmentName:String! = ""
    var departmentId:String! = ""
    

}


DepartmentProtocol.swift
import Foundation
import UIKit

@objc protocol DepartmentProtocol {

    
    func dressCode(departmentType:Int) -> UIColor
    
    func numberOfEmployees()->Int
    
    @objc optional func employeesInRange(fromDate:Date,toDate:Date) -> Int
}


Administration.swift
class Administration: Department , DepartmentProtocol {
    
    func dressCode(departmentType: Int) -> UIColor {
        return UIColor.blue
    }

    func numberOfEmployees() -> Int {
        return 4
    }
    
}


Finance.swift
import Foundation
import UIKit

class Finance: Department,DepartmentProtocol {
    
    func dressCode(departmentType: Int) -> UIColor {
        return UIColor.red
    }
    
    func numberOfEmployees() -> Int {
        return 10
    }
    
    func employeesInRange(fromDate: Date, toDate: Date) -> Int {
        return 5
    }
}


Observation's code

employessInRange is implemented in Finance.swift but not in Administration.swift. As that specific requirement is marked as optional.  Optional Requirements helps to write a code that interoperates with Objective C. Swift does not provide a way to write optional requirements directly. Hence we have to mention it with Objective C attribute.

@objc is the declaration attribute.

Note: 
- It is required both Protocol and the requirement  (i.e function employeesInRange) must be marked with @objc
- @objc protocol can be adopted only by the classes that inherit from Objective-C.  Hence, can't @objc can't be adopted by Structure and Enumeration in that scenario.


Comments

Post a Comment

Popular posts from this blog

hitTest on iOS to identify the view being hit

-
Image
HitTest on iOS Use hitTest, to identify the view being tapped. The below method allows us to identify the view being selected. We can use it, to identify the view from which we would like to hide the touch events or identify the view we are interested into. Example: In the below case when we tap on Black View we can show an alert like "Black View tapped!" , if we tap on Red View , we can show an alert  "You are not allowed to tap on Red View" .  override func hitTest ( _ point: CGPoint , with event: UIEvent ?) -> UIView ? { } Here is a simple implementation of the method, to identify the view being hit. View hierarchy being used is listed below:- Blue(parent) - Red(child) - Green(child) - Yellow (child) - Orange (child) - Black (child) - White (child) So lets' start with override of hitTest method.      override func hitTest ( _ point: CGPoint , with event: UIEvent ?) -> UIView ? {         //1         if let viewAvailable = findPoin
Read more

CMTimeMakeWithSeconds explained

-
Image
CMTime  is structure which has two main components,  timeScale  and  value. CMTIME = VALUE  / TIMESCALE where, TimeScale =  fraction of a second each unit in numerator occupies. CMTIME = Value / TimeScale 1)  public   func  CMTimeMake( _  value:  Int64 ,  _  timescale:  Int32 ) ->  CMTime CMTimeMake ( 6000 ,  10 ) Means, there are 6000 units , each unit occupies 1/10 of a second 2)  public   func  CMTimeMakeWithSeconds( _  seconds:  Float64 ,  _  preferredTimescale:  Int32 ) ->  CMTime CMTimeMakeWithSeconds(10.0,500) 10.0 = VALUE /500 Therefore VALUE = 5000 So, there are 5000 units, each occupy 1/500 of a second
Read more

Custom Editing Control for UITableViewCell , like iPhone Mail Appliation

-
Image
Dear Friends, Today, while I was developing a application, I found that I am in need to a custom Editing control. Custom Editing Control are displayed on the left side of the screen. IOS sdk provides two of such kind which we use most of the time UITableViewCellEditingStyleDelete & UITableViewCellEditingStyleInsert  . I will be now discussing the third one, UITableViewCellEditingStyleNone. This can be used to design our own Editing control. How this is going to look like can be fond from below screen shot. Steps to achieve this can be found below: STEP 1: Create A subclass of UITabelViewCell First create a subclass of UITableViewCell, where when the cell object is initialised we will have to add a UIButton to its view. You will also need a offset variable, whose value will be 32.0 in all iPhones. -( id ) initWithCoder:( NSCoder *)aDecoder{          self =[ super initWithCoder :aDecoder];          if ( self ){         offset =32.0;        
Read more