Swift - A way to force redrawing of UIScrollView - ios

Question

I have an UIViewController where there is an UIScrollView, there also is a function (build()) to draw UIView's in the UIScrollView.
Problem : Nothing appears in the UIViewController, but when I scroll (so when I update the UIScrollView) the UIView's, I wanted, appear.
I tried setNeedsDisplay() to force the redrawing but it doesn't work...
A video to help you to understand the problem :
https://vimeo.com/user87689481/review/281597574/3cccb78dc1
Here is the code of the UIViewController:
import UIKit
class MainViewController: UIViewController {
#IBOutlet weak var body: UIScrollView!
override func viewDidLoad() {
super.viewDidLoad()
// Do any additional setup after loading the view, typically from a nib.
navigationController?.navigationBar.prefersLargeTitles = true
navigationController?.navigationItem.largeTitleDisplayMode = .always
DispatchQueue.global(qos: .background).async {
while !Home.accessories.isInitialized {}
DispatchQueue.main.async {
self.build(Home.accessories.toUIView())
}
}
}
override func didReceiveMemoryWarning() {
super.didReceiveMemoryWarning()
// Dispose of any resources that can be recreated.
}
public func build(_ s: [UISectionView]) {
let topMargin = 10
let rightMargin = 10
let leftMargin = 10
let space = 5
let heightItem = 60
var b = topMargin
for t in s {
if t.isHidden == true {
continue
}
if t.title != nil {
let f = UIFont(name: "Helvetica", size: 20)
let l = UILabel(frame: CGRect(x: rightMargin, y : b, width: Int(UIScreen.main.bounds.width) - (rightMargin + leftMargin), height: Int(f!.lineHeight)))
l.font = f
l.text = t.title
body.addSubview(l)
b = b + Int(f!.lineHeight) + space
}
for i in t.items {
body.addSubview(i.getView(frame: CGRect(x: rightMargin, y: b, width: Int(UIScreen.main.bounds.width) - (rightMargin + leftMargin), height: heightItem), view: self))
b = b + heightItem + space
}
}
body.contentSize = CGSize(width: UIScreen.main.bounds.width, height: CGFloat(b))
//a code to force body (UIScrollView) to refresh/relaod/redraw/update/...
}
}
I hope we can help me =D
Thanks in advance !

Answer 1

There is no method to redraw a UIScrollView, then only thing you need to do is:
Add views to UIScrollView
Set contentSize of the UIScrollView so that it allows user to pan around and see all of the contents of the UIScrollView
What you are doing in your code seems ok, because you are doing both of the things listed above.
Problem is either if your ts are hidden:
if t.isHidden == true {
continue
}
Or you are calling build() method somewhere else on the Background thread
To be sure you are not doing that you can just add assert(Thread.isMainThread, "Never call me on background thread") as the first line in build() method