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Showing posts with label Protocol. Show all posts
Showing posts with label Protocol. Show all posts

Some truths about protocol

Q1 : Can structure confirm protocol?
A1 : Yes

Q2 : Can enumeration confirm protocol?
A2 : Yes

Q3 : Can we declare variable in protocol?
A3 : Yes -> It must be var and it must be read-Only or readAndWrite . Property declaration is like following : 

protocol someprotocol {
     var gettable : Int { get }
      var setAndGettable : Int { get set }

Q4 : Can we add function in enumeration?
A4 : Yes

Q5 : Can protocol has own init method?
A5 : Yes

Q6 : Can protocol inherit another protocol?
A6 : Yes
protocol someprotocol : anotherprotocol {

}

Q7 : Can we make class specific protocol?
A7 : You can limit protocol adoption to class types (and not structures or enumerations) by adding the AnyObject or class protocol to a protocol’s inheritance list.

protocol someprotocol : AnyObject, Someanotherprotocol {
}

Now someprotocol can only be confirmed by class-type. No strcture or enum type can confirm this protocol.

Q8. Can we declare optional protocol method in swift?
A8. Yes. In that protocol name and optional methods should be followed by @objc due to it consider as objective c code.

@objc protocol someprotocol {
        @objc optional func somemethod()
        @objc optional var someName : String { get set }
}

Q.9 Can protocol be fileprivate?
A9. Yes. Protocol can be fileprivate, private, public. Private and fileprivate protocol can be confirmed only within current file.


What is delegate?

Ans : Delegate is means of communication between objects of iOS Applications. Delegate allows one object to send message to another object when an event occurs.

i.e
UIAlertView *alert = [[UIAlertView alloc] initWithTitle:@”title” message:@”message” delegate:self cancelButtonTitle:@”Ok” otherButtonTitle:nil];

Here delegate is self. So now self is responsible for handling  all event fired by this instance of UIAlertView class.

Which button of UIAlertView is clicked, for that, event is clickedButtonAtIndex is called in or by Self or currentViewController.

Create PreDefined delegate :

  1. There are two ViewController NameVC and SurNameVC.
  2.  In NameVC, there are 2 textfield named as Name and FullName and 1 button as Submit.
  3. If I write in name and click on submit, it went to SurNameVC to take Surname parameter.
  4. On SurNameVC, after write Surname, on clicking of Submit, It call delegate method and went back to NameVC and Print Full Name in FullName textfield.

Implement above delegate and protocol in Objective-C : 


I have made protocol on SurNameVC like
    @protocol SurNameVCDelegate
      -(void)setSurName:(NSString *) strSurName;
    @end
    
    @property (nonatomic, retain) id delegate;

Now on NameVC submit button click, choose delegate of  SurNameVC object as self.

   objSurNameVC.delegate = self

and create method -(void)setSurName:(NSString *) strSurName;

on NameVC and it is called from surNameVC submit button. So setSurName is delegate method. We can print fullname by concatenating Name and Surname in FullName textfield.

So we delegate just pass message from one view controller to another view controller by delegate method.

Implement delegate and protocol in Swift

I have made custom UISlider. I want to send some value from custom UISlider value changed to view controller in which it is used. So for that, I have used delegate - protocol method.

customSlider.swift  Custom Slider file


import UIKit
protocol SliderDelegate: class {
    func sliderValueChanged(_ sender : UISlider)
}


class mpgpsSlider: UIView {
     
      weak var delegateSliderDelegate?

      required init?(coder aDecoder: NSCoder) {

        super.init(coder: aDecoder)
        
        let bundle = Bundle.init(for: type(of: self))
        let nib = UINib(nibName: "Slider", bundle: bundle)
        let view = nib.instantiate(withOwner: self, options: nil)[0] as! UIView
        view.frame = bounds
        view.autoresizingMask = [.flexibleWidth,.flexibleHeight]
        addSubview(view)
        
        slider.addTarget(self, action: #selector(sliderValueChanged(_:)), for:                  .valueChanged)
    }

     @objc func sliderValueChanged(_ sender : UISlider)  {
        delegate?.sliderValueChanged(sender)
      }

}

ViewController.swift ViewController in which custom slider is used.

import UIKit

class VehicleProfileVC: BaseViewController,SliderDelegate{
    
    override func viewDidLoad() {
        super.viewDidLoad()
        slider.delegate = self
    }
    
    func sliderValueChanged(_ sender: UISlider) {
        label.text = String(sender.value)
    }
}