What are UITextField delegate methods?

Ans : 

Copy from Apple Developer Site : Link

Managing Editing

func textFieldShouldBeginEditing(UITextField) -> Bool

Asks the delegate if editing should begin in the specified text field.

func textFieldDidBeginEditing(UITextField)

Tells the delegate that editing began in the specified text field.

func textFieldShouldEndEditing(UITextField) -> Bool

Asks the delegate if editing should stop in the specified text field. 

func textFieldDidEndEditing(UITextField, reason: UITextField.DidEndEditingReason)

Tells the delegate that editing stopped for the specified text field.

func textFieldDidEndEditing(UITextField)

Tells the delegate that editing stopped for the specified text field.

enum UITextField.DidEndEditingReason

Constants indicating the reason why editing ended in a text field.

Editing the Text Field’s Text

func textField(UITextField, shouldChangeCharactersIn: NSRange, replacementString: String) -> Bool

Asks the delegate if the specified text should be changed. 

func textFieldShouldClear(UITextField) -> Bool

Asks the delegate if the text field’s current contents should be removed.

func textFieldShouldReturn(UITextField) -> Bool

Asks the delegate if the text field should process the pressing of the return button.

Instance Methods

func textFieldDidChangeSelection(UITextField)

Which delegate method called when I click on push notifications?

Ans : 
Different app delegate method called depends on following scenarios

For silent notification : 

App is in Foreground
No system alert shown
application:didReceiveRemoteNotification:fetchCompletionHandler: is called

App is in Background
System alert is shown
application:didReceiveRemoteNotification:fetchCompletionHandler: is called

App is in Suspended
App state changes to Background
System alert is shown
application:didReceiveRemoteNotification:fetchCompletionHandler: is called

App is Not Running because killed by user
System alert is shown
No callback is called

Normal Push Notification (no content-available) :

App is in Foreground
No system alert shown
application:didReceiveRemoteNotification:fetchCompletionHandler: is called

App is in Background or Suspended
System alert is shown
No method is called, but when user tap on the push and the app is opened
application:didReceiveRemoteNotification:fetchCompletionHandler: is called

App is in Not Running
System alert is shown
No method is called, but when user tap on the push and the app is opened
application:didFinishLaunchingWithOptions: then application:didReceiveRemoteNotification:fetchCompletionHandler: are both called

Difference between Delegate and NSNotification

Ans :  A delegate uses protocol and creates a has-a relationship between two classes. Benefit of delegate is that we can return something back to the owning class.

Notification is like point to multi-point communication. Notification is one way  of message transmitting way.

Delegates create relationship between two classes. Notifications are used to send events to one or many classes.

We have to use delegate to specified known object. Notification for all object.

Delegate is like talking over telephone. Notification is like radio station.  

Coding of NSNotificationCenter :

[[NSNotificationCenter defaultCenter] addObjserver:self selector:@selector(useNotificationWithString:)  name:@”TimeOut” object:nil];

For BroadCast,

[[NSNotificationCenter defaultCenter] postNotificationName:@”TimeOut” object:nil userInfo:dict];

-(void) useNotificationWithString:(NSNotification *)notification

{

            dict = [notification userInfo];

}

To Remove observer,

[[NSNotificationCenter defaultCenter] removeObserver];

Coding of Delegate

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 delegate : SliderDelegate?

      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)

    }

}

Difference between Delegate and Datasource

Ans :

A delegate type object responds to actions that another object takes.

i.e  the UITableViewDelegate protocol has methods such as didSelectRowAtIndexPath for performing actions upon a user selecting a particular row in a table and willDisplayCell which called before delegate use cell to draw row.

DataSource type object gives data to another object.

i.e UITableViewDataSource protocol has methods such as cellForRowAtIndexPath and numberOfSectionInTaboeView dictating what should be displayed in the table.

Understanding Delegate in More Detail : 

If Object X call Object Y to perform an action. Object X should know when Object Y complete task and take action after that. 

Here we can tell that X is delegate object of Y. Y will have a reference of X. So X will implement delegate methods of Y. So Y can notify to X via delegate method.

One more point we can say that Delegate about controlling of UI and DataSource about controlling data.

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