Setup:
I have a ViewController ProblemView and class A. I pass ProblemView to class A, so I can work on it. It looks like this (simplified):
class ProblemView: UIViewController{
var instanceOfA = A()
instanceOfA.passView(passedVC: self)
}
class A{
var workOn = ProblemView()
func passView(passedVC: ProblemView){
workOn = passedVC
// I noticed, if I declare a varible locally like var workOn2 = passedVC, my problem is solved -
// but I need the variable globally, because I don't want to pass it around within this class
}
func doSth(){
// here I interact with variables of the passed ViewController
}
}
Problem: Whenever I restart this process within the app the memory increases every single time until I get memory error.
What I tried: I added deinit to both classes. class A is always deinitialized but class ProblemView is not (this might be the problem?).
I also found out, that when I don't declare workOn globally but within the passView function, then it works just fine. But I need have the variable globally, because I use it within many different functions of A. What could be a solution or workaround to this problem?
Strong references to each other.
Try to change class A:
weak var workOn: ProblemView?
func passView(passedVC: ProblemView){
workOn = passedVC
// I noticed, if I declare a varible locally like var workOn2 = passedVC, my problem is solved -
// but I need the variable globally, because I don't want to pass it around within this class
}
func doSth(){
// here I interact with variables of the passed ViewController
}
Related
I am writing my project and wondered.
When I read literature or watch videos, I see that this is bad practice. Why? Is this bad for the system?
What is the difference between this
class SomeClass {
var someView = SomeView()
var someViewModel = SomeViewModel()
// ...
}
and this
class SomeClass {
var someView: SomeView!
var someViewModel: SomeViewModel?
// ...
}
How to get used to it better?
You have to initialize all instance properties somehow. And you have to do it right up front, either in the declaration line or in your init method.
But what if you don't actually have the initial value until later, like in viewDidLoad? Then it is silly to supply a real heavyweight value only to replace it later:
var v = MyView()
override func viewDidLoad() {
self.v = // get _real_ MyView and assign it in place of that
}
Instead, we use an Optional to mark the fact that we have no value yet; until we obtain and assign one, it will be nil:
var v : MyView? // means it is initially `nil`
override func viewDidLoad() {
self.v = // get _real_ MyView and assign it to our property
}
There's nothing wrong with the first way (which is called a "default property value", by the way), and in fact, often times it's preferable. But of course, the devil is in the details:
How would the initialization of a SomeViewModel work? Without acess the initializer parameters of SomeClass, you're stuck with only being able to construct an instance from a parameter-less init, like SomeViewModel(). What exactly could that do? Suppose it was a person view model, and you had PersonViewModel(). What person? Whats their name? What will this default value do at all?
It's not a great pattern if it requires overwriting the default value with some other value in the initializer
It initializes the value up-front, where sometimes a lazy or computed value might be more appropriate.
I have a NSViewController that has a class variable as follows:
class ServerAdminViewController: NSViewController, NSTextFieldDelegate, MyTableViewDelegate {
var myClass = MyClass()
func showAdmin(window: NSWindow, myClass: MyClass) {
self.myClass = myClass
window.makeKeyAndOrderFront(self)
NSApp.activate(ignoringOtherApps: true)
}
An instance of this class is instantiated in the App initialization. Later when user clicks on a menu item, I want to show a window and use that value as a singleton for the app, during the time this window is open, also being able to modify myClass. However, the line where the instance variable is declared is being executed multiple times and after the self.myClass = myClassassignment, resetting the object (this is a menubar app that opens a window).
Tried
Several things, ex. removing the parameterless constructor from myClass, declaring that variable private and with a "!", adding init methods to the ViewController (without success) and some other failed attempts.
Question
How to make myClass a singleton and share it accross the application (i.e. make it available to this window) without reinitializing it?
Soo there use to be a bunch of stuff to do this with dispatchOnce and things like that. But now the way I do this is by declaring a shared static variable on my class. This will not handle persistence but it will solve your problem creating your class many times. The shared reference with only be recreated on use after being released. Or if it has never been used before. The class variable is also handy for retrieving the class for many controllers.
class MyClass {
static let shared = MyClass()
}
class MyViewController: UIViewController {
let myClass = MyClass.shared
}
Ok, I'm probably missing something super basic. I have an instance property called currentValue, initialized to be a String.
class ViewController: NSViewController {
var currentValue = ""
// ...
func getNewValue() {
currentValue = computeNewValue()
aLabel.stringValue = currentValue
}
func calledLater() {
println("\(currentValue)")
}
}
When I call getNewValue(), the label updates correctly.
But, when I call calledLater(), the currentValue is "reset" to an empty string.
At first I thought it was a weak storage thing but Swift apparently defaults to strong storage?
I tested this by initializing currentValue to "a" and, again, the label updates correctly, but when I get the variable later it returns "a".
I feel like I'm missing something but can't word it in a way that will let me do correct research.
You might be calling the methods on different instances of your 'ViewController' class.
(A typical scenario is when loading controllers from a storyboard; it "looks" like instances in the storyboard, but they are really just blueprints.)
I am trying out to create a singleton in SWIFT and this is what I have done so far
class Global {
class var sharedInstance:Global {
struct singleton {
static let instance:Global = Global()
}
return singleton.instance
}
}
var a = Global.sharedInstance
var b = Global()
if a === b {
println("Pointing to Same Instance")
}
else {
println("Pointing to different instance")
}
I have used computed type property to create a singleton (learnt that from another stackoverflow question).As of now the output is "Pointing to different instance".
What I am looking for is "a" and "b" in above example points to different instance of GLOBAL class and this breaks the point of singleton. How to make "a" and "b" in above example to point to the same instance of the class.
Thank you
This pattern does not guarantee there will only ever be one instance of the Global class. It just allows for anyone to access a single common instance of Global via its sharedinstance property.
So Global() declares a new instance of the Global class. But Global.sharedinstance does not create a new instance of Global, just fetches a pre-created one (that is created the first time anyone accesses it).
(If you alter your declaration of b to read var b = Global.sharedinstance you’ll see it confirms that a and b are pointing to the same instance.)
If you want to ban the creation of further instances of Global, make its init private:
private init() { }
But bear in mind you’ll still be able to create other Globals from within the file in which it’s declared, so if you’re doing the above in a playground or single-file test project, you won’t see any effect.
Class instance once in App life cycle.
class AccountManager {
static var sharedInstance = AccountManager()
var userInfo = (ID:"Arjun",Password:"123")
private init(){
print("allocate AccountManager")
}
}
here we set Private because :
Private access restricts the use of an entity to the enclosing declaration, and to extensions of that declaration that are in the same file. Use private access to hide the implementation details of a specific piece of functionality when those details are used only within a single declaration.
also set static property of sharedInstance
because if you need to access class property without instance of class you must have to declare "Static".
i got two swift files :
main.swift and view.swift
In main.swift i have a variable (Int) initially set to 0.
With an IBACtion I set that variable to be 10, and everything is ok.
However, if I try access that variable from view.swift, with a simple call like main().getValue(), i get always 0 and not 10 even if the variable has changed it's value in main.swift.
The method getValue() in main.swift looks like this:
func getValue() -> Int {
return variable
}
EDIT
Here is the code (Translated from Italian :D )
import Cocoa
class Main: NSObject {
var variable: Int = 0
func getValue() -> Int {
return variable
}
#IBAction func updateVar(sender: AnyObject!) {
variable = 10
}
}
class View: NSView {
override func drawRect(dirtyRect: NSRect) {
println(Main().getValue()) //Returns always 0
}
}
Thanks in advance
Alberto
I have solved this by creating a generic main class which is accessible to all views. Create an empty swift file, name it 'global.swift' and include it in your project:
global.swift:
class Main {
var name:String
init(name:String) {
self.name = name
}
}
var mainInstance = Main(name:"My Global Class")
You can now access this mainInstance from all your view controllers and the name will always be "My Global Class". Example from a viewController:
viewController:
override func viewDidLoad() {
super.viewDidLoad()
println("global class is " + mainInstance.name)
}
There is an important distinction to be made between "files" in Swift and "classes". Files do not have anything to do with classes. You can define 1000 classes in one file or 1 class in 1000 files (using extensions). Data is held in instances of classes, not in files themselves.
So now to the problem. By calling Main() you are creating a completely new instance of the Main class that has nothing to do with the instance that you have hooked up to your Xib file. That is why the value comes out as the default.
What you need to do, is find a way to get a reference to the same instance as the one in your Xib. Without knowing more of the architecture of your app, it is hard for me to make a suggestion as to do that.
One thought, is that you can add a reference to your Main instance in your Xib using an IBOutlet in your View. Then you can simply do self.main.getValue() and it will be called on the correct instance.