Two similar classes show different initialization errors - ios

Question

I found an error when I test some codes from Github.
class Profile {
let text: String
let date: String
let id: String?
init?(data: NSDictionary?) {
if let text = data?.valueForKeyPath(Test.Text) as? String {
self.text = text
if let date = data?.valueForKeyPath(Test.Created) as? String {
self.date = date
id = data?.valueForKeyPath(Test.ID) as? String
}
}else{
return nil
}
}
struct Test {
static let Text = "text"
static let Created = "created"
static let ID = "id"
}
}
The line of init? shows the error "constants self.data used before being initialized."
And I create a similar class of it, like
class Context {
let words: String
init?(text:String?) {
if let words = text {
self.words = words
}else{
return nil
}
}
}
This time it shows " all stored properties of class instance must be initialized before returing nil from an initializer."
For the first one , there is a workaround that I can delete the else block and give each properties an empty value would fix the error. However it would have me change the properties mutable.
( I don't want it to be mutable)
And for the second example, I just insert self.word = ""before the line of return nil could also fix the error.
But I really wonder why these similar cases show the different errors and realize the logic of Swift, and how can I fix it correctly?
Thank you for helping me.

Answer 1

Try this version of the code.
Code 1:
class Profile {
var text: String = ""
var date: String = ""
var id: String? = ""
init?(data: NSDictionary?) {
if let text = data?.valueForKeyPath(Test.Text) as? String {
self.text = text
if let date = data?.valueForKeyPath(Test.Created) as? String {
self.date = date
id = data?.valueForKeyPath(Test.ID) as? String
}
}else{
return nil
}
}
struct Test {
static let Text = "text"
static let Created = "created"
static let ID = "id"
}
}
Code 2:
class Context {
var words: String = ""
init?(text:String?) {
if let words = text {
self.words = words
} else {
return nil
}
}
}

Answer 2

York initializers are incomplete and that's why you get the message. Swift is type save, which means that all non optional properties must be initialized before the class is returned. Even when the class returns a nil. secondly, you can't call self (which is the class itself) if you haven't initialized the class. However, that should not be a problem in your case, since you've defined a root class. For your first class, please, implement the code like this and it should work.
class Profile {
struct Test {
static let Text = "text"
static let Created = "created"
static let ID = "id"
}
let text: String
let date: String
let id: String?
init?(data: NSDictionary?) {
guard let tempText = data?.valueForKeyPath(Test.Text) as? String else {
text = ""
date = ""
id = nil
return nil
}
text = tempText
if let tempDate = data?.valueForKeyPath(Test.Created) as? String {
date = tempDate
id = data?.valueForKeyPath(Test.ID) as? String
} else {
date = ""
id = nil
}
}
}
For the second class you need to do a similar thing, which means in the else statement give words a value and it should be okay.