What is the purpose of an iOS delegate?

Question

I understand what a delegate does in iOS, and I\'ve looked at sample code, but I\'m just wondering about the advantages of this type of encapsulation (as opposed to includin

Answer 1

Delegation as I understand it is when an object will pass the responsibility of handeling an event to another object thus "delegating" the responsibility to that object.

For example if you have an NSButton in iOs you generally assign the Delegate to be the parent view controller. This means instead of handeling touchUp events in the definition of the button it is instead handled in the view controller.

Answer 2

In iOS ecosystem especially UIKit Framework which consists of UIApplication, UITableView, UICollectionView, UITextfield & so on uses delegate & datasource design pattern intensively to communicate data to and fro.

Delegate design pattern is used to pass/communicate data from FirstVC(Delegator) to SecondVC(Delegate) to complete a task. Here, SecondVC(Delegate) conforms to a protocol delegate & implements all its requirements like methods by providing body to complete that task given by FirstVC(Delegator). Also, FirstVC(Delegator) object will be having a optional property of protocol delegate type i.e delegate which must be assigned by SecondVC(Delegate).

Now, FirstVC(Delegator) can call that method residing in SecondVC(Delegate) by passing data from its delegate property.

EX: CEO(FirstVC) which passes data i.e "confidential data" to Secretary(SecondVC) to do further processes using that data.

Datasource design pattern is part of Delegate pattern which is used to pass/communicate data from SecondVC(Delegate) to FirstVC(Delegator) when a task is assigned to SecondVC(Delegate). Here, SecondVC(Delegate) conforms to a protocol datasource & implements all its requirements like methods with return type by providing body to talk back to FirstVC(Delegator) after the task is given by FirstVC(Delegator). Also, FirstVC(Delegator) object will be having an optional property of protocol dataSource type i.e dataSource which must be assigned by SecondVC(Delegate).

Now, FirstVC(Delegator) can call that method with a return type residing in SecondVC(Delegate) by passing data from its dataSource property.

EX: Secretary(SecondVC) replies back with a data i.e "Sir, I am already having too much work to do. Please, can you assign that data to others" to CEO(FirstVC). Now, CEO(FirstVC) will analyse that data to do further processes.

Answer 3

Delegation is a design pattern not only used in iOS but many other languages. It enables you to hand values and messages over in your class hierarchy.

Answer 4

The most common use of a delegate in iOS is to establish communication within modules that are unrelated or partially related to each other. For example, passing data forward in a UINavigationController is very easy, we can just use segue. However, sending data backwards is little tricky. In this case, we can use delegate to send the data backward.

Let's call, the class, associated with the first Controller ClassA and the class, associated with the second Controller ClassB. The first Controller is connected to the second controller with a forward segue. We can pass data from ClassA to ClassB through this segue. Now, we need to pass some data to ClassA from ClassB for which we can use delegates.

The sender class(ClassB) needs to have a protocol in its header file(.h) and also a reference of it as delegate inside the block, @interface ClassB .... @end. This reference let's the ClassB know that it has a delegate. Any class that wants to use this ClassB will have to implement all of this protocol's required methods(if any). So, the receiver class,ClassA will implement the method but the call will be made by the sender class, ClassB.

This way, receiver class doesn't need to worry about the sender class' internal structure, and can receive the required information.

Answer 5

Delegation means one object passes behaviour to another object..