What is delegate in Objective C?

What is delegate in Objective C?

A delegate is an object that acts on behalf of, or in coordination with, another object when that object encounters an event in a program. The delegating object is often a responder object—that is, an object inheriting from NSResponder in AppKit or UIResponder in UIKit—that is responding to a user event.

What is delegate and datasource?

The data source provides information about what to display, like how many rows, and what goes in each row. The delegate tells the tableview what to do when the user selects a row, or whether the user is allowed to edit a row, and other things like that.

What is delegate protocol?

Delegates are a use of the language feature of protocols. The delegation design pattern is a way of designing your code to use protocols where necessary. In the Cocoa frameworks, the delegate design pattern is used to specify an instance of a class which conforms to a particular protocol.

How do I create a custom delegate in Swift?

Key Steps to Delegation

1. Create a delegate protocol that defines the messages sent to the delegate.
2. Create a delegate property in the delegating class to keep track of the delegate.
3. Adopt and implement the delegate protocol in the delegate class.
4. Call the delegate from the delegating object.

Why we use delegates in iOS?

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.

What is delegate in iOS with example?

Example for Delegate Let’s assume an object A calls an object B to perform an action. Once the action is complete, object A should know that B has completed the task and take necessary action. This is achieved with the help of delegates. A will implement the delegate methods of B.

What is a data delegate?

A delegate is an object-oriented, managed, secure and type-safe function pointer in the . NET framework. A delegate signature includes its name, return type and arguments passed to it. Rather than passing data, a delegate passes a method to another method.

What is the difference between data source and delegate?

A data source is almost identical to a delegate. The difference is in the relationship with the delegating object. Instead of being delegated control of the user interface, a data source is delegated control of data.

What are protocols Objective-C?

Objective-C allows you to define protocols, which declare the methods expected to be used for a particular situation. This chapter describes the syntax to define a formal protocol, and explains how to mark a class interface as conforming to a protocol, which means that the class must implement the required methods.

What is Delegates in Swift with example?

In Swift, a delegate is a controller object with a defined interface that can be used to control or modify the behavior of another object. One example is the UIApplicaitonDelegate in an iOS app.

What happens after a delegate object is created?

After a delegate is created, the method it is associated with never changes; delegate objects are immutable. Calling a delegate. After a delegate object is created, the delegate object is typically passed to other code that will call the delegate.

Why is delegate property declared weak in Objective-C?

A delegate property is always declared weak (notice the assign attribute). This is to break any potential retain cycle introduced. Consider an object that is the delegate of a table view. It will likely hold a strong reference to the table view because it owns the table view and might want to manipulate the table view.

Which is an example of a delegate in iOS?

The simplest example of a delegate that you’ll use almost every day as an iOS developer is UITableViewDelegate. If you look up the definition for this, it defines a large number of methods, but cutting it down to just one looks like this: The table view itself has a reference to its delegate, declared as a property:

How are delegation and notifications used in Objective-C?

Delegation is a way to pass a message up the tree to its owner. On the other hand, notifications are a way to message between completely separate parts of the object tree, where it would be extremely clunky to pass messages all the way up the tree to be distributed back down.