I am trying to instantiate an object from a class in swift. When I instantiate I am getting this error:
'Human'cannot be constructed because it has no accessible initializers
My Codes:
class Human{
var firstName: String
var lastName : String
var age : Int
var spouseName: String?
var childName : String?
var currentSpeed: Double = 0
func walk(speedIncrease: Double){
currentSpeed += speedIncrease*2
}
func brake(){
self.currentSpeed = 0
}
}
let tanvir = Human(firstName: "tanvir", lastName:"Alam", age: 32, currentSpeed:30)
print("gmk")
What am I doing wrong? Please Explain. Thank You.
Unlike structs where the initializer is synthesized classes require an explicit init method.
Add
init(firstName : String, lastName: String, age: Int, currentSpeed: Double = 0.0 {
self.firstName = firstName
self.lastName = lastName
self.age = age
self.currentSpeed = currentSpeed
}
and remove the default value of currentSpeed
A much simpler solution is to replace class with struct.
Related
I'm trying to use realmSwift in my application in Swift 4 but i have an error.
public class Test : Object {
#objc dynamic var id: Int = 0
#objc dynamic var long: Double? = 0
convenience init(id: Int, long:Double?) {
self.init()
self.id = id
self.long = long
}
override public class func primaryKey() -> String {
return "id"
}
}
Error for line with long variable.
Property cannot be marked #objc because its type cannot be represented in Objective-C
Thx for help
As the docs clearly state, numeric types cannot simply be marked Optional, because Optional numeric types cannot be represented in Objective-C. You need to use RealmOptional to store Optional numeric types in Realm classes.
public class Test : Object {
#objc dynamic var id: Int = 0
let long = RealmOptional<Double>()
}
You have provided Int value to the double, so it's throw error. Use following code for double;
#objc dynamic var value: Double = 0.0
I hope this will fix your issue.
For more info: https://realm.io/docs/swift/latest#property-attributes
How do you initialize your classes/structs with a lot of properties?
This question could probably be asked without Swift context but Swift brings a flavour to it, so I add Swift tag in headline and tags.
Let's say you have a User class with 20 properties. Most of them should not be nil or empty. Let's assume these properties are not interdependent. Let's assume that 33% of it should be constant (let) by the logic of the class. Let's assume that at least 65% of them do not have meaningful default values. How would you design this class and initialize an instance of it?
So far I have few thoughts but none of it seems to be completely satisfactory to me:
put all of the properties linearly in the class and make huge init method:
class User {
// there is 20 properties like that
let id : String
let username : String
let email : String
...
var lastLoginDate : Date
var lastPlayDate : Date
// then HUUUUGE init
init(id: String,
username: String,
...
lastPlayDate: Date) {
}
}
try to group properties into sub types and deal with smaller inits separately
class User {
struct ID {
let id : String
let username : String
let email : String
}
struct Activity {
var lastLoginDate : Date
var lastPlayDate : Date
}
let id : ID
...
var lastActivity : Activity
// then not so huge init
init(id: ID,
...
lastActivity: Activity) {
}
}
another solution is to break requirements a bit: either declare some of the properties optional and set values after init or declare dummy default values and set normal values after init, which conceptually seems to be the same
class User {
// there is 20 properties like that
let id : String
let username : String
let email : String
...
var lastLoginDate : Date?
var lastPlayDate : Date?
// then not so huge init
init(id: String,
username: String,
email: String) {
}
}
// In other code
var user = User(id: "1", username: "user", email: "user#example.com"
user.lastLoginDate = Date()
Is there a nice paradigm/pattern how to deal with such situations?
You can try the builder pattern.
Example
class DeathStarBuilder {
var x: Double?
var y: Double?
var z: Double?
typealias BuilderClosure = (DeathStarBuilder) -> ()
init(buildClosure: BuilderClosure) {
buildClosure(self)
}
}
struct DeathStar : CustomStringConvertible {
let x: Double
let y: Double
let z: Double
init?(builder: DeathStarBuilder) {
if let x = builder.x, let y = builder.y, let z = builder.z {
self.x = x
self.y = y
self.z = z
} else {
return nil
}
}
var description:String {
return "Death Star at (x:\(x) y:\(y) z:\(z))"
}
}
let empire = DeathStarBuilder { builder in
builder.x = 0.1
builder.y = 0.2
builder.z = 0.3
}
let deathStar = DeathStar(builder:empire)
Example taken from here: https://github.com/ochococo/Design-Patterns-In-Swift
If you are looking for a bit more Java like solution, you can try something like this.
Alternative Example
final class NutritionFacts {
private let servingSize: Int
private let servings: Int
private let calories: Int
private let fat: Int
private let sodium: Int
private let carbs: Int
init(builder: Builder) {
servingSize = builder.servingSize
servings = builder.servings
calories = builder.calories
fat = builder.fat
sodium = builder.sodium
carbs = builder.carbs
}
class Builder {
let servingSize: Int
let servings: Int
private(set) var calories = 0
private(set) var fat = 0
private(set) var carbs = 0
private(set) var sodium = 0
init(servingSize: Int, servings: Int) {
self.servingSize = servingSize
self.servings = servings
}
func calories(value: Int) -> Builder {
calories = value
return self
}
func fat(value: Int) -> Builder {
fat = value
return self
}
func carbs(value: Int) -> Builder {
carbs = value
return self
}
func sodium(value: Int) -> Builder {
sodium = value
return self
}
func build() -> NutritionFacts {
return NutritionFacts(builder: self)
}
}
}
let facts = NutritionFacts.Builder(servingSize: 10, servings: 1)
.calories(value: 20)
.carbs(value: 2)
.fat(value: 5)
.build()
Example taken from: http://ctarda.com/2017/09/elegant-swift-default-parameters-vs-the-builder-pattern
I would like to reduce the length of init method.
struct Person {
var id: Int
var firstName: String
var lastName: String
var vehicle: String
var location: String
var timeZone: String
init (id: Int, firstName: String, lastName: String, vehicle: String, location: String, timeZone: String ) {
self.firstName = firstName
self.lastName = lastName
self.vehicle = vehicle
self.location = location
self.timeZone = timeZone
}
}
Below is an instance of Person I am creating. I have to pass in the value of every single variable inline.
let person = Person(id: 22, firstName: "John", lastName: "Doe", vehicle: "Chevy", location: "Dallas", timeZone: "CST")
Question: How can I shrink the length of init? In Obj-C I used to create a data model class. Populate it's variables and then pass the entire class, reducing the length of the init method.
i.e.
Person *person = [Person new];
person.id = 22;
person.firstName = "John";
person.lastName = "Doe";
person.vehicle = "Chevy";
person.location = "Dallas";
person.timeZone = "CST"
Person *person = [Person initWithPerson:person];
What's an equivalent way in Swift to reduce the length of init without having to initialize every single variable inline? I know tuples is one way, is there any other best practice?
Just remove the initializer!
struct Person {
let id: Int
let firstName: String
let lastName: String
let vehicle: String
let location: String
let timeZone: String
}
Now you can use the memberwise initializer
Person(
id: 87112,
firstName: "Walter",
lastName: "White",
vehicle: "2004 Pontiac Aztek",
location: "Albuquerque",
timeZone: "UTC-07:00"
)
Structure types automatically receive a memberwise initializer if they do not define any of their own custom initialisers.
The Swift Programming Language
DO NOT use var
As you can see I replaced var with let.
Unless you need to change some properties of a Person after the value has been created, I suggest you to use let. Otherwise you are free to use var. This way the compiler will prevent unwanted changes.
DO NOT use Optionals
I don't know the business logic of your app, however if a Person must have all that 6 properties always populated, don't make them optionals. Otherwise every time you need to use a Person value the compiler will force you to check if that optional has a value.
DO NOT use Implicitly Unwrapped Optionals
Seriously. There are a few cases where they are useful and a model value is not one of them
Using a struct you actually don't need an initializer
struct Person {
var id : Int?
var firstName: String?
var lastName: String?
var vehicle: String?
var location: String?
var timeZone: String?
}
var person = Person()
person.id = 22
person.firstName = "John"
person.lastName = "Doe"
person.vehicle = "Chevy"
person.location = "Dallas"
person.timeZone = "CST"
You can do the same with non-optionals
struct Person {
var id = 0
var firstName = ""
var lastName = ""
var vehicle = ""
var location = ""
var timeZone = ""
}
Consider also the benefit of an initializer to declare (read-only) constants
struct Person {
let id : Int
let firstName : String
let lastName : String
let vehicle : String
let location : String
let timeZone : String
}
In this case you have to use the implicit memberwise initializer.
let person = Person(id: 22, firstName: "John", lastName: "Doe", vehicle: "Chevy", location: "Dallas", timeZone: "CST")
Like it was mentioned in the comments, an initializer will be created for you, and it'll look like this:
Person(id: Int?, firstName: String?, lastName: String?, vehicle: String?, location: String?, timeZone: String?)
However, you can also do this:
var person = Person()
person.id = 100
person.firstName = "Name"
...
Like you used to do in ObjC. Note that person was declared as var, because if it was declared as let, you wouldn't be able to mutate it.
Hi I am doing some Swift coding and I cant figure out how to get rid of this error:
Missing argument for parameter 'makePetMakeNoise' in call.
Could you help me fix this error?
import Foundation
import UIKit
class Human {
static var numCreated:Int = 4
var name:String = ""
var pet:Pet
init(name:String,pet:Pet){
self.name = name
self.pet = pet
Human.numCreated++
}
func makePetMakeNoise(){
var randomNumber = arc4random_uniform(9)
self.pet.makeNoise(randomNumber) //Missing argument for parameter 'makePetMakeNoise' in call
}
func feedPet(){
self.pet.eat
}
static func populationCount(){
println("Total population count is \(Human.numCreated)")
}
}
class Pet {
var name:String = ""
var noise:String = ""
var canMakeNoise:Bool = true
init(name:String,noise:String,canMakeNoise:Bool){
self.name = name
self.noise = noise
self.canMakeNoise = canMakeNoise
}
func makeNoise(canMakeNoise: Int, makePetMakeNoise: Int){
if self.canMakeNoise {
for _ in 1...5{
println("\(self.name) \(self.noise)")
}
}else {
println("\(self.name) *remains silent*")
}
}
func eat(){
println("\(name) is eating")
}
class Dog:Pet{
}
class Cat:Pet{
override func eat {
super.eat()
println("I'm still hungry, meow")
}
}
}
//Pets
var Tobie = Pet(name: "Tobie", noise: "Bark", canMakeNoise: true)
var Bud = Pet(name: "Bud", noise: "Bark", canMakeNoise: false)
var Ginger = Pet(name: "Ginger", noise: "bark", canMakeNoise: false)
var Curry = Pet(name: "Curry", noise: "Bark", canMakeNoise: true)
//Humans
var Sam = Human(name: "Sam", pet: Tobie)
var Mark = Human(name: "Mark", pet: Bud)
var Spencer = Human(name: "Spencer", pet: Ginger)
var Jessie = Human(name: "Jessie", pet: Curry)
let Humans = [Sam, Mark, Spencer, Jessie]
for Human in Humans {
println("\(Humans) \(feedPet) \(makePetMakeNoise)") //Use of unresolved identifier 'feedPet and makePetMakeNoise'\\
}
`
Your makeNoise method defined for Pet takes two parameters. Problem is that when you call it in the line that gives you the error, you pass it just one parameter.
Possible solution is:
Change the Pet's method as follow:
func makeNoise(makePetMakeNoise: Int){
if self.canMakeNoise {
for _ in 1...5{
println("\(self.name) \(self.noise)")
}
}else {
println("\(self.name) *remains silent*")
}
}
Update the code that gives you the error in Human like this:
func makePetMakeNoise(){
var randomNumber = Int(arc4random_uniform(9))
self.pet.makeNoise(randomNumber)
}
Notice I convert random to Int since this is the expected parameter type.
Please consider I'm just guessing a possible modification since I don't know what your classes are intended for ... maybe just a playground.
Other solution is effectively passing two parameters when you call the pet's method from human.
Hope this helps
Your function func makeNoise(canMakeNoise: Int, makePetMakeNoise: Int) expects two arguments, but your are only passing the one randonNumber in your call self.pet.makeNoise(randomNumber). It should look something like this: self.pet.makeNoise(randomNumber, someOtherNumber)
I am trying to override custom init in my code as you can see I am creating Player class with default and custom init
class Player{
//Properties
var name : String
var score : Int
//Methods
func description() -> String{
return( "Player \(name) has score \(score)")
}
//Default Initiallizer
init(){
name = "Sohrab"
score = 0
}
//Custom Initializer
init(name : String, score : Int){
self.name = name
self.score = score
}
}
and below I create PremierPlayer class
class PremierPlayer : Player {
//Properties
var memberLevel : String
//Method
override func description() -> String {
let originalMessage = super.description()
return ("\(originalMessage) is a \(memberLevel)")
}
//Default Initilizer
override init() {
memberLevel = "Gold"
super.init()
}
//Custome Initilizer
init(name: String, score: Int, memberLevel:String) {
self.memberLevel = memberLevel
super.init(name: <#String#>, score: <#Int#>)
}
}
In Line super.init(name: <#string#>, score: <#Int#>) i got an error ISSUE expected ',' separator
What should I do?
The formatting of your (current version of) question is rather confusing, but if you are talking about this line:
super.init(name: <#String#>, score: <#Int#>)
... then you should replace <#String#> with just value of String and <#Int#> with Int types. Those <#...#> are placeholders that XCode injects into code automatically for you to replace them with something sensible.