Could someone explain to me in a simple and clear way the difference between designated initializers and convenience initializers? If possible, with some basic example to understand it
Could someone explain to me in a simple and clear way the difference between designated initializers and convenience initializers? If possible, with some basic example to understand it
A class has a designated initializer, however, it may have several convenience initializers. The convenience initializers are helpers, they have to invoke the designated initializer of the same class, yes or yes (e.g. self.init(name: name, age: 8) ), to initialize the class. The convenience initializers are used because they are convenient , they usually have fewer parameters, giving a default value to the other parameters.
Example 1 : A class
class Animal {
var name: String
var age: Int
// designated initializer
init(name: String, age: Int) {
self.name = name
self.age = age
}
/// convenience initializer, gives a default age value
convenience init(name: String) {
self.init(name: name, age: 8)
}
}
let dog = Animal(name: "Beethoven")
print(dog.name)
Example 2 : A UIView subclass (without storyboard / xib)
UIView is a special case because it has two initializers, init(frame:) (when the view is initialized programmatically) and also init(coder:) (when the view is initialized from a storyboard or nib, that we can ignore because only Xcode calls this method when it creates the view from the storyboard / xib).
class AnimalView: UIView {
var name: String
var age: Int
// designated initializer
init(name: String, age: Int) {
self.name = name
self.age = age
super.init(frame: CGRectZero) // invocamos al designated initializer del superclass
}
/// convenience initializer, gives a default age value
convenience init(name: String) {
self.init(name: name, age: 8)
}
// No vamos a llamar a este método
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
let dog = AnimalView(name: "Beethoven")
print(dog.name)