I'm beginner in Swift development.
I saw a video about data modeling in Swift. This code below:
private var _name: String!
var name: String {
return _name
}
Why we need to do that? I know it's good but can you explain to me about how it's better than normal ways like just define directly.
It seems like in your case you will have Invalid redeclaration of name - variable.
private var _name: String!
name = "xyz" {
return _name
}
or
private var _name: String = ""
name {return _name}
Related
I have a struct that is used when parsing JSON data. I want one of the fields, name, to be a fixed name, see below...
struct QuestionConfiguration: Codable, DisplayOrderable {
var name: String? = "QuestionConfiguration"
var isRequired: Bool
var displayOrder: Int
var title: String = ""
var questions: [Question]
}
Each time, when I then try and access a QuestionConfiguration object, name is nil.
I have tried using an init(), with parameters and without.
I have tried String? and String.
Does anyone know how I can achieve this so that name is the same for each object, without having to pass it to the object?
Simply by changing this line - var name: String? = "QuestionConfiguration" to this - let name = "QuestionConfiguration"
Full code -
struct QuestionConfiguration: Codable, DisplayOrderable {
let name = "QuestionConfiguration"
var isRequired: Bool
var displayOrder: Int
var title: String = ""
var questions: [Question]
}
Note - If property is fixed then you should not call it as variable b'coz variable means it may change
I have my model called Restaurant:
realm object on kotlin:
class Restaurant : RealmObject {
#PrimaryKey
var _id: ObjectId = ObjectId.create()
var name: String = ""
var adress: String? = null
}
I want to use the _id property. But for that I need to convert to a String in SwiftUI
I tried: restaurant_id as! String, it does not work,
Is is related to this post: https://www.mongodb.com/community/forums/t/swift-convert-objectid-to-string/121829
No real answers there
Any other solutions?
the error when using .toHexString(): Value of type 'any Library_baseObjectId' has no member 'toHexString':
the type of _id in this case:
The error when trying: "\(restaurant._id.stringValue)"
I solved this by adding a getter to the class:
class Restaurant : RealmObject {
#PrimaryKey
var _id: ObjectId = ObjectId.create()
var name: String = ""
var adress: String? = null
fun getID() : String{
return _id.toString()
}
}
ObjectID's in Swift have a stringvalue property which returns the ObjectID as a string
You could do this
let idAsAsString = someRealmObject._id.stringValue
Or for kotlin and other SDK;s
let idAsString = object._id.toString()
In SwiftUI, the id can be accessed in a similar way, and then use the value to init a new string
let x = someRealmObject._id.stringValue
let y = String(stringLiteral: x)
let _ = print(x, y)
Text("\(x) \(y)")
and the output will be
6376886a1dbb3c142318771c 6376886a1dbb3c142318771c
in the console and the same in the Text in the UI
Here's some SwiftUI showing the use
List {
ForEach(myModel) { model in
NavigationLink(destination: SecondView(navigationViewIsActive: $navigationViewIsActive, selectedEntryToShow: model))
{
Text("\(model._id.stringValue)") //ormodel._id.toString()
}
}
}
This Swift model works perfectly and the string of ObjectId can be read per above.
class Restaurant: Object {
#Persisted(primaryKey: true) var _id: ObjectId
#Persisted var name: String = ""
#Persisted var adress: String? = null
}
I have seen this in some videos on Youtube.
class Student {
private var _name: String!
private var _studentID: Int!
var name: String {
return _name
}
var studentID:Int {
return _studentID
}
init(name: String, studentID: Int) {
self._name = name
self._studentID = studentID
}
}
Any reason why they are doing this (adding _name and _studentID) instead of:
class Student {
private var name: String!
private var studentID: Int!
init(name: String, studentID: Int) {
self.name = name
self.studentID = studentID
}
}
Thank you very much.
The first examples are essentially creating properties that are publicly readable but privately writable.
The second set of code does not do the same thing as the first set.
The proper way to write this code is:
private (set) var name: String // no need for the !
private (set) var studentID: Int // no need for the !
init(name: String, studentID: Int) {
self.name = name
self.studentID = studentID
}
This makes the properties readable by outside users but only settable by the class. This is what the 1st set of code implements but in a much more verbose and needless manner.
The use of underscore is just a naming convention carried over from Objective-C when creating private instance variables.
Personally, I'd avoid videos and tutorials that use the 1st set of code.
I am learning protocol oriented approaches and I am facing below issue when adding access modifiers.
I have an enum for mode type. It can be changed.
public enum ModeType: String {
case Smart = "Smart"
case Easy = "Easy"
}
I have created a protocol like below.
protocol Device {
var deviceID: String { get }
var title: String { get }
var currentMode: ModeType { get set }
}
And below class conforms to the Device protocol.
class DeviceList: Device {
public private(set) var currentMode: ModeType
public private(set) var deviceID: String
public private(set) var title: String
init(deviceID: String, title: String, currentMode: ModeType, waterLevel: String, humidityLevel: String) {
self.deviceID = deviceID
self.title = title
self.currentMode = currentMode
}
}
Issue is public private(set) var currentMode: ModeType
but below works
public internal(set) var currentMode: ModeType
What am I misunderstanding here can anyone explain?
I'm going to create a new class, and in this class there's a computed variable; so I'm looking for a way to init this variable:
import UIKit
class Squadra: NSCoder, NSCoding
{
var nomeSquadra: String
var numeroCoriSquadra: Int
var coloreSquadra: String
var immagineSquadra: String
var sottotitoloSquadra: String
{
get
{
return "I migliori cori: \(nomeSquadra)"
}
}
init(nome: String, numero: Int, colore: String, immagine: String, sottotitolo: String)
{
nomeSquadra = nome
coloreSquadra = colore
numeroCoriSquadra = numero
immagineSquadra = immagine
sottotitoloSquadra = sottotitolo
}
}
obviously with this line of code Xcode gives my a compile error (because the var is a get only property).
I think that i have to use a set to make the var writable, but I don't know how to operate because I don't know exactly how get and set work.
Either remove sottotitoloSquadra = sottotitolo or assign to a different variable. Even if the assignment worked, you never actually use the value that comes in as sottotitolo for anything.
I can't see useful behavior while you use independent property nomeSquadra and trying to have setter for sottotitoloSquadra at the same time. Maybe better to use hidden support property for computed variable in your case?
private var _sottotitoloSquadra: String
var sottotitoloSquadra: String
{
get
{
return "I migliori cori: \(_sottotitoloSquadra)"
}
set
{
_sottotitoloSquadra = newValue
}
}
init(nome: String, numero: Int, colore: String, immagine: String, sottotitolo: String)
{
//...
_sottotitoloSquadra = sottotitolo
}
If I understand you class correctly, you want to use the variable's default string when the init() did not provide a value (I'm just guessing though).
So if the team doesn't have a specific subTitle, you would make one up from the team's name.
I also understand that you don't want that property to be modifiable after the object is instantiated.
If that is the case, (I assume you would get an empty string for sottotitolo), you can define a private variable to hold the provided title and expose it using a computed variable. The default value (made up title) can be returned by that computed variable if a title was not supplied on the init().
class Squadra
{
var nomeSquadra: String
var numeroCoriSquadra: Int
var coloreSquadra: String
var immagineSquadra: String
private var _sottotitoloSquadra = ""
var sottotitoloSquadra: String
{
return _sottotitoloSquadra == ""
? "I migliori cori: \(nomeSquadra)"
: _sottotitoloSquadra
}
init(nome: String, numero: Int, colore: String, immagine: String, sottotitolo: String)
{
nomeSquadra = nome
coloreSquadra = colore
numeroCoriSquadra = numero
immagineSquadra = immagine
_sottotitoloSquadra = sottotitolo
}
}
Only your class, including its init() function, can modify the private variable holding the supplied sottotitolo. Outside of that source file, the private variable is not accessible at all.