UIScrollView showing subview not correctly - swift

Question

I'm trying to show simple custom view into scrollView. Here's my code :
struct scrollViewDataStruct {
let title: String?
let image: UIImage?
}
class ViewController: UIViewController {
#IBOutlet weak var scrollView: UIScrollView!
var scrollViewData = [scrollViewDataStruct]()
override func viewDidLoad() {
super.viewDidLoad()
scrollViewData = [
scrollViewDataStruct(title: "First", image: #imageLiteral(resourceName: "iPhone 8 Copy 2")),
scrollViewDataStruct(title: "Second", image: #imageLiteral(resourceName: "iPhone 8 Copy 3"))
]
self.scrollView.backgroundColor = .yellow
scrollView.contentSize.width = self.scrollView.frame.width * CGFloat(scrollViewData.count)
var i = 0
for _ in scrollViewData {
let view = CustomView(frame: CGRect(x: self.scrollView.frame.width * CGFloat(i), y: 0, width: scrollView.frame.width, height: self.scrollView.frame.height))
self.scrollView.addSubview(view)
i += 1
}
// Do any additional setup after loading the view, typically from a nib.
}
}
class CustomView: UIView {
let imageView: UIImageView = {
let imageView = UIImageView()
imageView.translatesAutoresizingMaskIntoConstraints = false
imageView.backgroundColor = UIColor.blue
return imageView
}()
override init(frame: CGRect) {
super.init(frame: frame)
self.addSubview(imageView)
imageView.leftAnchor.constraint(equalTo: self.leftAnchor).isActive = true
imageView.rightAnchor.constraint(equalTo: self.rightAnchor).isActive = true
imageView.topAnchor.constraint(equalTo: self.topAnchor).isActive = true
imageView.bottomAnchor.constraint(equalTo: self.bottomAnchor).isActive = true
}
required init?(coder aDecoder: NSCoder) {
fatalError("init(coder:) has not been implemented")
}
}
As you can see, the CustomView's frame = scrollView's frame but when i ran application it's not as I expected :
Then, in storyboard, i change device from iphone8 to iphone 8 plus and run again. It's show CustomView correctly. I have no idea, the scrollView is always correct but the CustomView is not .
Any suggest ?

Answer 1

Your problem is that you are accessing the frame of the scrollView before Auto Layout has run and established the size of the frame for the actual device. A quick fix is to move your setup code into an override of viewDidLayoutSubviews.
You have to be careful though, because unlike viewDidLoad, viewDidLayoutSubviews will run more than once, so you have to make sure you don't add your views multiple times.
// property - have we set up the views yet?
var setup = false
override func viewDidLayoutSubviews() {
super.viewDidLayoutSubviews()
if !setup {
scrollView.contentSize.width = self.scrollView.frame.width * CGFloat(scrollViewData.count)
var i = 0
for _ in scrollViewData {
let view = CustomView(frame: CGRect(x: self.scrollView.frame.width * CGFloat(i), y: 0, width: scrollView.frame.width, height: self.scrollView.frame.height))
self.scrollView.addSubview(view)
i += 1
}
setup = true
}
}
You should consider using constraints to place your views within your scrollView content instead of messing with the frame calculations, then Auto Layout would just automatically do the right thing.

Answer 2

In viewDidLoad, UI component will suppose to have the size you have taken in storyboard.
There are 2 ways to do this:
1. Use autoresizingMask property
autoresizingMask property will resize the view, if its containerView's frames changed
var i = 0
for _ in scrollViewData {
let view = CustomView(frame: CGRect(x: self.scrollView.frame.width * CGFloat(i), y: 0, width: scrollView.frame.width, height: self.scrollView.frame.height))
view.autoresizingMask = .flexibleHeight
self.scrollView.addSubview(view)
i += 1
}
2. Use fixed parameters, say UIScreen.main.bounds.size.height
Just update your code for custom view's height with reference to screen height rather than scroll view's height. It will work fine
var i = 0
let height = UIScreen.main.bounds.size.height
for _ in scrollViewData {
let view = CustomView(frame: CGRect(x: self.scrollView.frame.width * CGFloat(i), y: 0, width: scrollView.frame.width, height: height))
self.scrollView.addSubview(view)
i += 1
}