variable cannot be modified in another class - class

Question

am trying to modify a variable in another class, but it doesn't change.
class ViewController: UIViewController {
var t = 1
override func viewDidLoad() {
super.viewDidLoad()
t = 9
var pp = action().test()
println(pp) // got “2” here
}
the above should print "10" , but it shows "2".
another swift file:
class action {
var k = ViewController().t
func test()->Int{
k++
return k
}
}
Anything I made wrong?
Thnaks.

Answer 1

When you have a class with properties, and create an instance of that class, properties are bound to the class instance and not the class type. So if you create 2 instances of the same class their properties are independent, so if you change a property in one instance, that won't affect the same property in the other instance.
Note: by convention, in swift type names always start in uppercase, so I have renamed action to Action in my code.
Your code isn't working as expected because in the Action class you are creating a new instance of ViewController:
var k = ViewController().t
which has no relationship with the instance used to instantiate Action - so the new instance will have its t property set to 1.
The correct way to fix it is to pass the view controller instance to Action, and let it work on that instance.
class ViewController: UIViewController {
var t = 1
override func viewDidLoad() {
super.viewDidLoad()
t = 9
var action = Action(viewController: self)
var pp = action.test()
println(pp) // got “2” here
}
}
class Action {
var k: Int
init(viewController: ViewController) {
self.k = viewController.t
}
func test()->Int{
k++
return k
}
}
The above code should give an indication of what's wrong with your code, but it can be written in a better way. Action doesn't really need the ViewController instance, it just needs an integer passed in to its initializer, so a better way to achieve the same result is by modifying the code as follows:
class ViewController: UIViewController {
var t = 1
override func viewDidLoad() {
super.viewDidLoad()
t = 9
var action = Action(t: self.t)
var pp = action.test()
println(pp) // got “2” here
}
}
class Action {
var k: Int
init(t: Int) {
self.k = t
}
func test()->Int{
k++
return k
}
}