I am just getting into Swift and struggling how to simply set a text property of a label in one class based on a variable in another. In one swift file I have:
Class GameController:
var instructsText = String()
func gameControl()
instructsText = array[2] as string //this gets the instructions text from a Plist file.
In another swift file I have
Class HelpViews: UIView {
override init(frame: CGRect) {
// add the instructions label
var instructsLabel = UILabel(frame: CGRectMake(ScreenWidth/2-300, ScreenHeight-150, 600, 100))
instructsLabel.text = instructsText - ERROR 'instructs is not a subtype of 'NSString'
self.addSubview(instructsLabel)
any help very much appreciated!
It is unclear why you would be getting the error you say you are. At no point, (at least in the code above) do you make an object of the GameController Class and thus the compiler should be telling you that it does not recognize the variable instructsText. However, I would suggest using a computed class property. An example of one would be:
class MyClass {
class var pi: Double { return 3.1415926 }
// ...
}
println(MyClass.pi)
Which would print out 3.1415926. In you code, one way that might work is as follows:
Class GameController:
class var instructsText = String {return array[2] as String}
And in the HelpView Class:
Class HelpViews: UIView {
override init(frame: CGRect) {
// add the instructions label
var instructsLabel = UILabel(frame: CGRectMake(ScreenWidth/2-300, ScreenHeight-150, 600, 100))
instructsLabel.text = GameController.instructsText
self.addSubview(instructsLabel)
The Apple Swift documentation is here.
Try first to println(instructsText) variable, to see what you try to set.
Here is a few cases:
Not declared variable
It could be nil
It's not String
Related
There has been same titles of this question but different situations.
In this case this is very simple but I can't find a same problem online.
So here's the code
class ViewController: UIViewController {
#IBOutlet weak var fldTotalUnits: UITextField!
var intTotalUnits:Int? = Int(fldTotalUnits)
The error here says "Cannot use instance member 'fldTotalUnits' within property initializer;..."
I tried replacing var with let, I tried NSString, I tried .toInt() but nothign worked... so how do I this?
String to Int conversion is not complicated. You simply do the conversion at the wrong place. You are trying to reference one member in the initialization of another member, that is not allowed. In this particular case simply because fldTotalUnits has the value nil when you would try to use it via Int(fldTotalUnits). When creating an instance of your class ViewController fldTotalUnits is set to nil and initialized with a useful value later. Therefore what you have to do in the first place is move the line into a separate method:
func doSomething() {
var intTotalUnits:Int? = Int(fldTotalUnits)
}
Now you will see that the compiler complains about there not being a suitable initializer because you have to access the text property of fldTotalUnits instead of using the actual textfield:
func doSomething() {
var intTotalUnits:Int? = Int(fldTotalUnits.text!)
}
Now you can think about moving the declaration of intTotalUnits to somewhere else, but setting its value has to happen in some method.
The code in your question is trying to create an Int from a UITextField, not a String. What you should say is something like…
var intTotalUnits:Int?
func updateTotalUnits()
guard let text = fldTotalUnits.text else { return }
intTotalUnits = Int(text)
}
I want to write a function that takes a string and then prints the value of the class property with that name. In practice, there would be more than one property to choose form. For example...
class Apple{
var juiciness : Int = 0
init(juiciness: Int){
self.juiciness = juiciness
}
}
var myApple(juiciness : 10)
func printValue(property : String){
print(Apple.property) // <-- I want to use the string to choose a property
}
Obviously, I can't do this code but I know there has to be a better solution than just I series of if statements.
Apple has done this for you. It is known as key-value observing(KVO).
Try the following code in the playground:
let label = UILabel()
print(label.value(forKey: "font"))
Your own class can support KVO by inheriting from NSObject:
class YourClass: NSObject{ ... }
I would like to do something similar to the following with an NSObject subclass
class Thing: NSObject {
class func defaultText() -> String { ... }
let text: String
init(text: String?) {
self.text = text ?? self.dynamicType.defaultText() // Of course, this line won't compile
super.init()
}
}
so that Thing subclasses may override defaultText() without requiring them to override the initializer. This is easy to do with a mutable stored property, but it would be nice to have it constant. Is there a way to do this?
This is a separate issue than overriding static vars in subclasses swift 1.2 . There is no desire to override a constant or a static method. The only thing in question is, in the initializer where the constant is set, is there a way to compute a value based on the specific class that is being initialized?
I am having an issue with calling an instance method within the class itself. If someone can provide me some insight it would be greatly appreciated.
My current code looks like this:
class Rect
{
func printthis() -> String {
return "this is working or what"
}
var toPrint:String = self.printthis()
}
The error I am getting in Xcode is: Use of unresolved identifier 'self'.
What am I missing here?
You can't call an instance method without an instance. The class is merely the template for instances. So i don't what you are trying to do here...
But the answer is no, you cannot call an instance method form the class definition because there is no instance yet.
Perhaps you want to delcare a class method and use that to set an instance variable on creation? If so, you might do that like this:
class Rect {
class func printthis() -> String {
return "this is working or what"
}
var toPrint:String
init() {
toPrint = Rect.printthis()
}
}
var r = Rect()
println(r.toPrint) //-> this is working or what
An instance of a class is not initialized and able to be referenced (even as 'self') until all of its variables have been assigned values.
An option that may work for you is to declare your variable as an implicitly-unwrapped optional, which is assigned nil by default. Then in the class's init method, since all of the variables have been assigned values, you are able to start calling methods on your instance.
class Rect {
var toPrint: String!
init() {
toPrint = printthis()
}
printthis() -> String {
return "this will work"
}
}
the problem is that swift is strict about initing all properties.
you may as a workaround
class Rect
{
func printthis() -> String {
return "this is working or what"
}
var toPrint:String = ""
init() {
toPrint = printthis()
}
}
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.