Swift class with uibutton.addTarget to UIView not working - ios

Question

I created a new file with the following class:
import Foundation
import UIKit
var Feld = classFeld()
class classFeld {
let button = UIButton()
func createButton() -> UIButton {
button.frame = CGRect(x: 10, y: 50, width: 200, height: 100)
button.backgroundColor=UIColor.black
button.addTarget(self, action: #selector(ButtonPressed(sender:)), for: .touchUpInside)
return button
}
#objc func ButtonPressed(sender: UIButton!) {
button.backgroundColor=UIColor.red
}
}
And this is my ViewController:
import UIKit
class ViewController: UIViewController {
override func viewDidLoad() {
super.viewDidLoad()
mainview.addSubview(Feld.createButton())
self.view.addSubview(mainview)
}
var mainview=UIView()
}
When I start the app a black button is created but when I click on it it doesnt color red.
If I add the button instead of
mainview.addSubview(Feld.createButton())
to
self.view.addSubview(Feld.createButton())
it works and the button turns red.
May I anyone explain me why? It should make no difference if I add something to self.view or to a subview which is then added to self.view?

Answer 1

Because you need to give it a frame and add it to self.view
var mainview = UIView()

Answer 2

This is because you are just initializing a UIView without giving it any frame and adding it to the main view.
You need to give frame to your mainview also. For example :
class ViewController: UIViewController {
var mainview = UIView()
override func viewDidLoad() {
super.viewDidLoad()
mainview.frame = CGRect(x: 10, y: 50, width: 300, height: 300)
self.view.addSubview(mainview)
mainview.addSubview(Feld.createButton())
}
}

Answer 3

Here is changes on ViewController class and working fine:
class ViewController: UIViewController {
var mainview: UIView!
override func viewDidLoad() {
super.viewDidLoad()
mainview = UIView(frame: self.view.bounds)
mainview.addSubview(Feld.createButton())
self.view.addSubview(mainview)
}
}