I have following code snippets:
protocol UpdateUIFromNativeListenerItf {
func triggerUI()
}
class WmBuildGroupsTask{
var mUfn:UpdateUIFromNativeListenerItf?
init(){/* ... */}
// ...
class func triggerRegister( ufn: UpdateUIFromNativeListenerItf ) {
mUfn = ufn // WmBuildGroupsTask.Type does not have `mUfn`
}
}
Form other class I call:
var ufn:UpdateUIFromNativeListenerItf = self
WmBuildGroupsTask.triggerRegister(ufn)
How can I pass delegate to static method?
Do I need create singleton for class WmBuildGroupsTask?
I tried also to write class var mUfn:UpdateUIFromNativeListenerItf?
But get: Class var not yet supported
Thanks,
Static stored properties are not supported in swift classes (yet), but they are in structs. So you can create an inline private struct and define your static properties there:
class WmBuildGroupsTask{
private struct Static {
static var mUfn:UpdateUIFromNativeListenerItf?
}
init(){/* ... */}
// ...
class func triggerRegister( ufn: UpdateUIFromNativeListenerItf ) {
Static.mUfn = ufn // WmBuildGroupsTask.Type does not have `mUfn`
}
}
The downside is that you have to access the static property prefixing it with the struct name - but I guess that's an acceptable tradeoff.
There is also another obvious way to solve the problem: turn the class into a struct, so obvious that it's enough to just mention it. Just a consideration: structs and classes are not interchangeable, they have their own pros and cons.
You are trying to access a member variable in a static context. mUfn is stored for an instance of your class, not for the class itself.
Related
I'm relatively new to swift and searched around but could not find any satisfactory answer to my problem. I would like to have a Singleton class instance which can be initialized with some variables. E.g.
public class Singleton {
var car: String
var bus: String
init(car: String, bus: String) {
self.car = car
self.car = bus
}
func drive() {
print("I will drive")
}
}
public class SingletonConsumer {
// create an instance of Singleton Once
var driver: Singleton = Singleton(car: "honda", bus: "volvo")
driver.drive()
}
public class driverClassWorld : SingletonConsumer {
driver.drive()
}
how can i achieve it? I tried protocol but issue i am hitting is how to instantiate singleton class with parameters.
I don't get this problem?
First remove singleton from your brain for a moment. Because I think you have the wrong idea on what a singleton is.
Now lets rephrase your question to: "How to instantiate a class with parameter"
Its like this:
import Foundation
class Test {
let someText : String!
init(something:String){
someText = something
}
func test(){
print("TEST \(someText)")
}
}
let a = Test(something: "Me")
a.test()
Output:
TEST Optional("Me")
You just need to define a init with the parameters you want.
Now to properly instantiate a singleton (basically it just the class above but single instance). There are a lot of ways, the old Objective C approach is still valid.
But for swift this is the most common pattern. You need to define a Static Property.
Example:
import Foundation
class Test {
static let shared = Test(something: "REAL SINGLETON")
let someText : String!
init(something:String){
someText = something
}
func test(){
print("TEST \(someText)")
}
}
Test.shared.test()
Output:
TEST Optional("REAL SINGLETON")
Now reread the definition of a singleton:
a singleton class is a class that can have only one object (an
instance of the class) at a time
For other patterns in declaring a singleton:
https://cocoacasts.com/what-is-a-singleton-and-how-to-create-one-in-swift
Now, you might wonder: When does this singleton instance instantiated?
Answer: It is when it is first used/called.
To create a singleton class, I wrote something like this:
class SingletonEx{
var name = ""
private init(){}
static let sharedInstance = SingletonEx()
func instanceMethod(){
}
static func classMethod(){
}
}
Some tutorials say final is necessary while others just ignore final keyword. After I tried subclassing SingletonEx, I got the following results.
It seems I can't write an initializer for subclass, which means I can't use an override instance method in a subclass.
As far as I know, singleton definition is all about single instantiation and accessing instance methods through the only instance. So I don't think it is necessary to use final in the singleton definition. But both my teachers and some online tutorials say it is necessary.
I got confused, since you can't create a subclass instance anyway, even you override the instance methods, you can't use it or access it, what's the point to say final is necessary for a singleton class?
If I am wrong, please point out.
Super Class
First of all you need to know the properties and methods that are marked with private are just known to the Super class and Sub classes won't access them!
A class can inherit methods, properties, and other characteristics from another class. When one class inherits from another, the inheriting class is known as a subclass, and the class it inherits from is known as its superclass. Inheritance is a fundamental behavior that differentiates classes from other types in Swift.
Classes in Swift can call and access methods, properties, and subscripts belonging to their superclass and can provide their own overriding versions of those methods, properties, and subscripts to refine or modify their behavior. Swift helps to ensure your overrides are correct by checking that the override definition has a matching superclass definition.
In your case in SingletonEx class you market init with private which means that you can create object just in the body of the class! that means no one, no where, can't create an object of SingletonEx!
If you want to a method end up in Super Class and you don't want to Sub classes overide that method you need to mark that method with final which means it's not private but its available only from Super class!
Sub Class
When class Y Inheritance from SingletonEx which means that cant create an object outside of the class ! because Super class initializer is unavailable during init() method from class Y ! While you need to call the super.init() if you want to initialize an object from Y class !
if you remove private from private init() {} from SingletonEx class you be able to create object from SingletonEx class and also from Y class !
your code should looks like this :
Swift 4 :
class SingletonEx{
var name = ""
init(){}
static let sharedInstance = SingletonEx()
func instanceMethod(){
}
static func classMethod(){
}
}
class Y : SingletonEx {
private var yName = "Y name is : "
init(name:String) {
super.init()
self.name = self.yName + name
}
}
Usage :
override func viewDidLoad() {
super.viewDidLoad()
let yObject = Y.init(name: "badGirl :D ")
print(yObject)
// --> Output : Y name is : badGirl :D
}
world! I have an Actions class, where I hold all actions, animations and sound-plays in my sprite-kit game. So in all my SKNode, SKScene, SKSpriteNode classes I always initialize this Actions class. Is this good for performance? Or I have to initialize this one once, for example in GameViewController and then pass a copy of this class to all other classes, where I need?
As Fogmeister has mentioned in his comment you can use static methods to achieve this. This should also help with performance.
If you check the SKAction documentation you will notice that it uses class vars and methods as well.
In general if you do not need to instantiate a class multiple times, which your case is a perfect example of, than its best to use static/class methods or Singletons.
You can either use a class, struct or enum. I prefer to use enums because you cannot instantiate them by accident or need to add a private initialiser.
// Class
class SKActionHelper {
static var someProperty = ...
static func someMethod() {
...
}
}
// Struct
struct SKActionHelper {
static var someProperty = ...
static func someMethod() {
...
}
}
// Enum
enum SKActionHelper {
static var someProperty = ...
static func someMethod() {
...
}
}
Now you can call those properties or methods anywhere in your project and do not need to instantiate the class each time.
SKActionHelper.someProperty = ...
SKActionHelper.someMethod()
Hope this helps
I have read the Swift docs and searched here, but I still am not sure about how to implement a class hierarchy where each subclass sets custom value for an inherited static property; that is:
Base class defines a static property: all instances share the same value.
Subclass overrides the static property: all instances share the same value, which is different form that of the base class.
Can the property be stored?
Also, How should I access the value of the property from within an instance method (regardless of the particular class), and get the correct value everytime? will the following code work?
class BaseClass
{
// To be overridden by subclasses:
static var myStaticProperty = "Hello"
func useTheStaticProperty()
{
// Should yield the value of the overridden property
// when executed on instances of a subclass:
let propertyValue = self.dynamicType.myStaticProperty
// (do something with the value)
}
You are so close to being there, except that you can't override a static property in a subclass — that is what it means to be static. So you'd have to use a class property, and that means it will have to be a computed property — Swift lacks stored class properties.
So:
class ClassA {
class var thing : String {return "A"}
func doYourThing() {
print(type(of:self).thing)
}
}
class ClassB : ClassA {
override class var thing : String {return "B"}
}
And let's test it:
ClassA().doYourThing() // A
ClassB().doYourThing() // B
I'd like to logically organize class properties to signify that they are one logical unit and to distinguish them from other class properties that are less tightly related.
I thought of doing this using a struct within my class. However, it seems that I can't call class methods from the struct property setters. I get what seems to be an inappropriate compile error: "missing argument for parameter #1 in call"
This seems to be different from calling method from struct in swift
where the function is within the struct. In my case, the methods are generic and don't just apply to my struct but to all class properties. Therefore, I don't want to move them within the struct.
Do you have ideas on how to organize properties into tight(er) logical units within classes?
class MyClass {
struct MyStruct {
static var aVarInMyStruct: String? {
didSet {
anotherVarInMyStruct = foo() // This gives compile error "missing argument for parameter #1 in call"
}
}
static var anotherVarInMyStruct: String?
}
func foo() {
println("I am foo()")
}
}
The inner type MyStruct knows nothing about its outer type MyClass. So there is no foo function to call from MyStruct. To better organize your code I suggest you to use // MARK: - whatever this section is comments. Types are not here to organize codes. Types are here to create right abstractions for the program.
I fix your bug:
class MyClass {
struct MyStruct {
static var aVarInMyStruct: String? {
didSet {
anotherVarInMyStruct = MyClass.foo() // This gives compile error "missing argument for parameter #1 in call"
}
}
static var anotherVarInMyStruct: String?
}
static func foo()->String {
println("I am foo()")
return "it is ok"
}
}