Central align subView - swift

Question

I'm trying to centre a UIView in another view (so like a pop up view), but whatever I do, I just cannot align it centrally!
func loadPopUpView() {
let customView = CGRect(x: view.center.x, y: view.center.y, width: 100, height: 100)
popUpView = UIView(frame: customView)
popUpView.backgroundColor = UIColor.black
view.addSubview(popUpView)
popUpView.isHidden = false
}
I've changed the background colour to black just so I know when it appears.
I cannot do this with storyboard because it's going on a tableView, so I'm trying to do it programmatically. Result Image

Answer 1

You also need to minus half value of your custom view height and width from x and y like below:
let customView = CGRect(x: view.center.x - 50, y: view.center.y - 50, width: 100, height: 100)

Answer 2

You are telling it to put top left corner in the center, hence you need to let it get half size in position.
let customView = CGRect(x: view.center.x-50, y: view.center.y-50, width: 100, height: 100)
Another solution is the use anchorpoints.
customView.centerXAnchor.constraint(equalTo: self.centerXAnchor).isActive = true
customView.centerYAnchor.constraint(equalTo: self.centerYAnchor).isActive = true
customView.heightAnchor.constraint(equalToConstant: 100).isActive = true
customView.widthAnchor.constraint(equalToConstant: 100).isActive = true

Answer 3

On CGRect(x:, y:, width:, height:), the point (x,y) is the origin. In iOS, that's the top left point.
On the CGRect doc:
In the default Core Graphics coordinate space, the origin is located
in the lower-left corner of the rectangle and the rectangle extends
towards the upper-right corner. If the context has a
flipped-coordinate space—often the case on iOS—the origin is in the
upper-left corner and the rectangle extends towards the lower-right
corner.
So to fix this:
let width = 100.0
let height = 100.0
let customViewFrame = CGRect(x: view.center.x - width/2.0, y: view.center.y - height/2.0, width: width, height: height)
Another solution would be to apply the center once the frame (especially the width/size) have been set.
let customViewFrame = CGRect(x: 0, y: 0, width: 100, height: 100)
customViewFrame = view.center