Accessing view controller methods inside another class [Swift] - ios

Question

I am using UITableViewDiffableDataSource for my tableview's dataSource by creating a UITableViewDiffableDataSource class inside my ViewController (AnimalsVC). Whenever I try to get my ViewController's data array (or any other variables/functions) from inside my data source class I get this error:
Instance member 'animalsArray' of type 'AnimalsVC' cannot be used on an instance of nested type 'AnimalsVC.DataSource'
I am not sure why I'm getting this error because my DataSource class is inside my ViewController class. Here is my code:
class AnimalsVC: UIViewController {
var animalsArray = []
class DataSource: UITableViewDiffableDataSource<Int, Animal> {
override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
let items = animalsArray //<- This is where the error occurs
return true
}
}
}

Answer 1

I am not sure why getting this error because my DataSource class is inside my ViewController class.
That makes no difference. Declaring one class inside of another merely namespaces the inner class, i.e. it is now called AnimalsVC.DataSource. It does not cause one instance of the inner class to be able to see magically inside an instance the outer class (and indeed it is completely unclear what instances we would be talking about).
Your nesting of class declarations is useless, so you might as well not do it.
Instead, if DataSource needs to see inside AnimalsVC, do what you would normally do: give your DataSource instance a reference to the AnimalsVC instance:
class AnimalsVC: UIViewController {
var animalsArray = // ...
}
class DataSource: UITableViewDiffableDataSource<Int, Animal> {
weak var vc : AnimalsVC?
// ...
}
When you create your DataSource instance, set its vc to self. Now the DataSource can consult the instance properties of the AnimalsVC instance.
(Actually, what I do in my own code is give my UITableViewDiffableDataSource subclass a custom designated initializer. That way, I can create the data source and hand it a reference to the view controller all in one move.)

Answer 2

In order to access the outer class from the inner, you need to pass a reference in to it. It is not automatic, as with Java, for instance.
Assuming the Animal object is defined elsewhere, then what you could do is:
class AnimalsVC: UIViewController {
var animalsArray = [] as [Animal]
class DataSource: UITableViewDiffableDataSource<Int, Animal> {
var myanimal:AnimalsVC
init(animal: AnimalsVC){
myanimal = animal
super.init()
}
override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
let items = myanimal.animalsArray //<- This should not be an error any more
return true
}
}
}

Answer 3

The data should be contained in the DataSource class. Move your animalsArray into DataSource class.
If you need to access it easily from anywhere, declare it under DataSource as:
static var animalsArray = [Animal]()
You can then access it from anywhere using DataSource.animalsArray, such as:
DataSource.animalsArray.append(animal)
I guess you could create it as a static var under AnimalsVC instead, but the data should really be declared in the data source.
This would make your class look like this:
class AnimalsVC: UIViewController {
class DataSource: UITableViewDiffableDataSource<Int, Animal> {
static var animalsArray = [Animal]()
override func tableView(_ tableView: UITableView, canEditRowAt indexPath: IndexPath) -> Bool {
let items = DataSource.animalsArray
return true
}
}
}

Answer 4

It is not possible because.
"NestedTypes" it is not possible to access instance member or function
in other class even Container class unlike "Inheritance" that you can
access instance member or function of parent class.
If you want your implementation work with no error. "Static" will help you.
struct Animal {
var label: String
}
class AnimalVC {
static var animals: [Animal] = []
var dataSource = DataSource()
class DataSource {
func add(_ animal: Animal) {
animals.append(animal)
}
func display() {
print(animals.map { $0.label })
}
func remove(_ index: Int) -> String? {
guard index < (animals.count - 1) else { return nil }
return animals.remove(at: index).label
}
}
func load() {
dataSource.display()
dataSource.add(Animal(label: "Dog"))
dataSource.display()
for i in ["Cat", "Fish", "Bird"] {
dataSource.add(Animal(label: i))
}
dataSource.display()
print(vc.dataSource.remove(AnimalVC.animals.count) ?? "Cannot delete.")
}
}
Test.
let vc = AnimalVC()
vc.load()
NestedTypes
convenient to define utility classes and structures purely for use within the context of a more complex typequote
Inheritance
Inherits characteristics from the existing class
Source
NestedTypes: https://docs.swift.org/swift-book/LanguageGuide/NestedTypes.html
Inheritance :https://docs.swift.org/swift-book/LanguageGuide/Inheritance.html