I am new to iOS development . I wanted to create a dictionary which is looks like
var userInformation: UserInformation = UserInformation()
var genericDictionary: Dictionary<Int,userInformation> = [Int:userInformation]()
here ,userInformation is an object of UserInformation class .
class UserInformation{
var name:String?
var phonenumber:String?
init(_ name:String ,_phoneNumber:String){
self.name = name
self.phoneNumber = phoneNumber
}
and lastly i tried genericDictionary.append(). i wanted to store name and phone number here. i don't know how it works!
i tried , but it shows various kinds of error. is it possible to do this ?
Problem is in declaration of dictionary with value type you are specifying the object that you have created instead of its type, means it should be UserInformation class type instead of instance of it userInformation. Try like this way.
var genericDictionary = [Int:UserInformation]()
Edit: With latest edit of your question I thin'k you are looking for array not dictionary, if it is true try like this way.
var array = [UserInformation]()
array.append(userInformation)
Do like this :
var genericDictionary : [Int : UserInformation] = [:]
You are declaring the dictionary using a variable instead of the class. Instead of userInformation, you need to use UserInformation like this:
var genericDictionary: Dictionary<Int,UserInformation> = [Int:UserInformation]()
Related
Sorry if the title is rather confusing, but I'm curious to know the difference between these two lines:
var title = String()
var title: String
Is one being initialized and one only be declared? Which is more correct?
For example, if I have a struct should I use one of the other?
So the reason I ask this is because I'm learning about how to grab some JSON from a url and then display it in my app. One of the new ways of doing so is using Decodable. So, I have a struct in a model class like so:
struct Videos: Decodable {
var title = String()
var number_of_views : Int
var thumbnail_image_name: String
var channel: Channel
var duration: Int
}
In another class I have this:
URLSession.shared.dataTask(with: url){(data,response,error) in
if(error != nil){
print(error!)
return
}
guard let data = data else { return }
do{
self.Videos2 = try JSONDecoder().decode([Videos].self, from: data)
//self.collectionView?.reloadData()
}catch let jsonErr{
print(jsonErr)
}
}.resume()
So, should I declare or initialize the variables in my struct? I'm assuming I should just declare them like so:
var title: String?
Would that be the correct syntax in my struct?
UPDATE:
I understand this question was more broad then I originally proposed it to be. I'm sorry about that, but thank you so much for all your great answers that clarified a lot up for me.
The difference is that : defines the type of your variable, whereas = assigns an actual value to the variable.
So:
var title = String()
This calls the initializer of the String type, creating a new String instance. It then assigns this value to title. The type of title is inferred to be String because you're assigning an object of type String to it; however, you could also write this line explicitly as:
var title: String = String()
This would mean you are declaring a title variable of type String, and assigning a new String to it.
var title: String
This simply says you're defining a variable of type String. However, you are not assigning a value to it. You will need to assign something to this variable before you use it, or you will get a compile error (and if this is a property rather than just a variable, you'll need to assign it before you get to the end of your type's init() method, unless it's optional with ? after it, in which case it gets implicitly initialized to nil).
EDIT: For your example, I'd probably declare all the variables using let and :, assuming that your JSON provides values for all of those properties. The initializer generated by Decodable should then set all the properties when you create the object. So, something like:
struct Videos: Decodable {
let title: String
let number_of_views : Int
let thumbnail_image_name: String
let channel: Int
let duration: Int
}
This initializes a value
var title = String()
This declares a value but does not initialize it
var title: String
If you attempt to use the latter, such as print(title), you will get a compiler error stating Variable 'title' used before being initialized
It does not matter whether the value is a class or a struct.
The = operator is the assignment operator, it assigns a value to the object on the left of the =
Typically, class or struct properties are declared but not initialized until the init() is called. A simple class might be
class MyClass {
let myProperty: String
init(aString: String) {
self.myProperty = aString
}
}
Whereas inside the scope of a function you may declare a local variable that only lives inside the scope of the function.
func doSomethingToAString(aString: String) -> String {
let extraString = "Something"
let amendedString = aString + extraString
return amendedString
}
In your specific example, the struct synthesizes an initializer that will allow you to initialize the struct with all the values needed to fill your properties. The initializer generated by Decodable should then set all the properties when you create a Videos struct, you will do it something like:
let aVideos = Videos(title: "My Title", number_of_views: 0, thumbnail_image_name: "ImageName", channel: Channel(), duration: 10)
Is one being initialized and one only be declared?
Yes, meaning that the declared cannot be used. If you tried to set a value for it, you would get a compile-time error:
variable 'title' passed by reference before being initialized
Which is more correct?
There is no rule of thumb to determine which is more correct, that would be depends on is there a need to initialize title directly.
On another hand, when it comes to declare properties for a class, saying var title = String() means that you are give title an initial value ("") which means that you are able to create an instance of this class directly, example:
class Foo {
var title = String()
}
let myFoo = Foo()
However, if title declared as var title: String, you will have to implement the init for Foo:
class Foo {
var title: String
init(title: String) {
self.title = title
}
}
let myFoo = Foo(title: "")
Also, you have an option to declare it as lazy:
lazy var title = String()
which means:
A lazy stored property is a property whose initial value is not
calculated until the first time it is used. You indicate a lazy stored
property by writing the lazy modifier before its declaration.
Properties - Lazy Stored Properties
I am completely new in swift and iOS developing.
I want to initialize this array
I defined the array like this when my class starts
var i = 0
var ArrayTitle = [NSString]()
and then I need to initialize it in one of the functions like this
let ArrayTitl[i] = "text"
and I checked it even like this but the error is same
let ArrayTitl[0] = "text"
but it has this Error
Cannot assign to immutable expression of type '[Int]'
Appreciate any help. thanks
You are using a dynamic array so you need to append the value.
Here's a small exemple:
var arrayTitle = [String]()
arrayTitle.append("text")
print(arrayTitle[0]);
Let's say I have a class that has 10 properties. I have an XML response (AEXMLDocument in this case) where the element tags match the property names exactly. Is there a way I could populate the values in a for loop rather than writing out 10 lines of code? I used ***property.name**** to show where I would like to put these variables. That part is not actually in the code.
class User(){
var firstName = String()
var lastName = String()
var middleName = String()
...
var property10 = String()
}
func populateUser (xml: AEXMLDocument) -> User{
var returnUser = User()
for property in xml.root["SOAP-ENV:Body"]["ns1:getUserResponse"]["return"].children{
returnUser.***property.name*** = property.value
}
return returnUser
You can use setValue(_, forKey:) method as long as you subclass from NSObject.
If the class inherits from NSObject, you can use key-value coding:
returnUser.setValue(property.value, forKey: property.name)
Be careful with this though. Anyone who can modify the XML sent to your app can modify any property on the User object.
I have a small problem in swift. Let's say I have a class called Pet.
Pet has a variable for name and noise, created like so:
class Pet
{
var name : String = ""
var canMakeNoise : Bool = true
}
Now, when I call initialise the class creating let's say a cat, I can easily do it like so:
var cat: Pet()
cat.name = "Garfield"
cat.canMakeNoise = false
This works smoothly, however when trying to pass it in directly using literal values like so:
let cat : Pet("Garfield",true)
or
let cat : Pet(name:"Garfield",canMakeNoise:true)
I get this error:
Swift Compile Error - Extra Argument in call
Why is that? How can I fix it? Thanks in advance.
If you want to add arguments to the initializer than you need to specify a new init function instead of relying on the default one. Here's how you'd do it in your case:
class Pet {
var name : String = ""
var canMakeNoise : Bool = true
init( name : String, canMakeNoise : Bool ) {
self.name = name
self.canMakeNoise = canMakeNoise
}
}
var kitty = Pet(name: "Cat", canMakeNoise: true)
Since you use default values for your variables, xCode does not find a need for initializer. So when you create a new instance of the class it will be a Pet with name = ”” and canMakeNoice = true.
If you want to change these default values you will need to supply a init method (and you can than remove these default values)
class Pet{
var name:String
var canMakeNoise:Bool
init(name:String, canMakeNoise:Bool){
self.name = name
self.canMakeNoise = canMakeNoise
}
convenience init (name:String){
self.name = name
self.init(name:name, canMakeNoise: true)
}
}
I’ve supplied two init methods here. The first one takes 2 arguments:
var cat: Pet = Pet(name: "Kitten", canMakeNoise: true)
This will create a Pet with the supplied name and the supplied canMakeNoise.
If you want to you can also supply a convenience init This is a shortened init. In this case used to be able to make another instance of the Pet class.
var dog: Pet = Pet(name: "Doggy")
As you see we don’t supply the canMakeNoise property here cause the convenience initializer does that for us (and uses true as the canMakeNoice)
I have been learning the swift language. I setup this vocabulary class and using this class to generate a new object "newWord". I put this object into a new Array "vocabularyListb". When I try to get the newWord.name property from the array, it returns "nil". So the question is how can I access the property of an Object that resides in an Array?
class vocabulary{
let name:String
init(name: String){
self.name = name
}
}
let vocabularyList1a = ["instigate", "constitution", "bellow", "jargon", "term"]
var vocabularyList1b = [AnyObject]()
var newWord = vocabulary(name: vocabularyList1a[0])
newWord.name
vocabularyList1b.append(newWord)
vocabularyList1b[0].name
At the moment you instantiate your vocabularyList1b as [AnyObject]. But you actually want to have an array of vocabulary objects.
So you will have to change :
var vocabularyList1b = [AnyObject]()
To:
var vocabularyList1b = [vocabulary]()
After that you can access the name variable.