UIView not showing in UIViewcollection in Swift, Programmatically - ios

Question

the below code is the viewController that is navigated with a navigationItem navigationItem.leftBarButtonItem = UIBarButtonItem(title: from a previous tableViewController and I am trying to produce a UIView in my viewController. However nothing is showing.
import UIKit
class SecondpgController: UIViewController {
var inputContainerView: UIView!
override func viewDidLoad() {
super.viewDidLoad()
view.backgroundColor = UIColor .gray
let inputContainerView = UIView()
self.view.addSubview(inputContainerView)
//inputContainerView.backgroundColor = UIColor(red: 162/255, green: 20/255, blue: 35/255, alpha: 1)
inputContainerView.backgroundColor = .white
inputContainerView.translatesAutoresizingMaskIntoConstraints = false
//inputContainerView.topAnchor.constraint(equalTo: self.view.topAnchor, constant: 300).isActive = true
//nputContainerView.leftAnchor.constraint(equalTo: self.view.leftAnchor, constant: 10).isActive = true
inputContainerView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor, constant: 200).isActive = true
inputContainerView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor, constant: 200).isActive = true
The app is running well however after reaching the view controller, Nothing is shown but only a grey screen.
Why is this happening and how can I solve it?

Answer 1

Your problem is that you constraints are only setting x and y position for the UIView you are creating. You are missing width and height.
Try this constraints:
inputContainerView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor).isActive = true
inputContainerView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor).isActive = true
inputContainerView.widthAnchor.constraint(equalToConstant: 100).isActive = true
inputContainerView.heightAnchor.constraint(equalToConstant: 100).isActive = true
This code means that your UIView will be centred vertically and horizontally in your self.view and also it has a width and height of 100. It will look like this:
Hope it helps. Happy Coding

Answer 2

You have added constraints to place inputContainerView to the centre of the screen but did not add constraints for it's height and width. Adding the following code might solve your issue:
inputContainerView.centerXAnchor.constraint(equalTo: self.view.centerXAnchor, constant: 0).isActive = true
inputContainerView.centerYAnchor.constraint(equalTo: self.view.centerYAnchor, constant: 0).isActive = true
inputContainerView.addConstraint(NSLayoutConstraint(item: inputContainerView, attribute: .height, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 200))
inputContainerView.addConstraint(NSLayoutConstraint(item: inputContainerView, attribute: .width, relatedBy: .equal, toItem: nil, attribute: .notAnAttribute, multiplier: 1, constant: 200))
Check this: https://developer.apple.com/library/content/documentation/UserExperience/Conceptual/AutolayoutPG/ProgrammaticallyCreatingConstraints.html
Ensure that the constants for CenterXAnchor and CenterYAnchor are 0, so the view aligns at the centre. And make sure you add inputContainerView only once either as an outlet or programmatically.