Get offset when Scrollview is animated - ios

Question

I have a scorll view with animating
UIView.animate(withDuration: Double(totalMidiTime) / 1000, delay: 0, options: .curveLinear) {
self.scrollView.contentOffset.x = self.scrollView.contentSize.width - self.leftMargin
} completion: { (_) in }
I want to get current postion offset when it's animating

Answer 1

You can get the offset by checking the bounds.origin.x value of the scroll view's presentation layer:
guard let pl = scrollView.layer.presentation() else {
return
}
print("Content Offset X:", pl.bounds.origin.x)
Here's a complete example...
We create a scroll view with 30 labels. On viewDidAppear we start a 20-second horizontal animation to the last label. Each time we tap the button, the "status label" will update with the current bounds.origin.x of the scroll view's presentation layer (which matches the contentOffset.x):
class ViewController: UIViewController {
let scrollView: UIScrollView = {
let v = UIScrollView()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .systemGreen
return v
}()
let testButton: UIButton = {
let v = UIButton()
v.translatesAutoresizingMaskIntoConstraints = false
v.backgroundColor = .blue
v.setTitle("Get Offset", for: [])
v.setTitleColor(.lightGray, for: .highlighted)
return v
}()
let statusLabel: UILabel = {
let v = UILabel()
v.translatesAutoresizingMaskIntoConstraints = false
v.numberOfLines = 0
v.textAlignment = .center
v.text = "Content Offset X\n0.00"
return v
}()
override func viewDidLoad() {
super.viewDidLoad()
let stack = UIStackView()
stack.distribution = .fillEqually
stack.spacing = 8
stack.translatesAutoresizingMaskIntoConstraints = false
for i in 1...30 {
let v = UILabel()
v.backgroundColor = .yellow
v.text = "Label \(i)"
v.textAlignment = .center
stack.addArrangedSubview(v)
}
scrollView.addSubview(stack)
view.addSubview(scrollView)
view.addSubview(testButton)
view.addSubview(statusLabel)
let g = view.safeAreaLayoutGuide
let cg = scrollView.contentLayoutGuide
let fg = scrollView.frameLayoutGuide
NSLayoutConstraint.activate([
scrollView.topAnchor.constraint(equalTo: g.topAnchor, constant: 20.0),
scrollView.leadingAnchor.constraint(equalTo: g.leadingAnchor, constant: 20.0),
scrollView.trailingAnchor.constraint(equalTo: g.trailingAnchor, constant: -20.0),
scrollView.heightAnchor.constraint(equalToConstant: 60.0),
stack.topAnchor.constraint(equalTo: cg.topAnchor, constant: 8.0),
stack.leadingAnchor.constraint(equalTo: cg.leadingAnchor, constant: 8.0),
stack.trailingAnchor.constraint(equalTo: cg.trailingAnchor, constant: -8.0),
stack.bottomAnchor.constraint(equalTo: cg.bottomAnchor),
stack.heightAnchor.constraint(equalTo: fg.heightAnchor, constant: -16.0),
testButton.topAnchor.constraint(equalTo: scrollView.bottomAnchor, constant: 20.0),
testButton.centerXAnchor.constraint(equalTo: g.centerXAnchor),
testButton.widthAnchor.constraint(equalTo: g.widthAnchor, multiplier: 0.6),
statusLabel.topAnchor.constraint(equalTo: testButton.bottomAnchor, constant: 20.0),
statusLabel.centerXAnchor.constraint(equalTo: g.centerXAnchor),
statusLabel.widthAnchor.constraint(equalTo: g.widthAnchor, multiplier: 0.9),
])
testButton.addTarget(self, action: #selector(gotTap(_:)), for: .touchUpInside)
}
override func viewDidAppear(_ animated: Bool) {
super.viewDidAppear(animated)
UIView.animate(withDuration: 20.0, delay: 0, options: .curveLinear) {
self.scrollView.contentOffset.x = self.scrollView.contentSize.width - self.scrollView.frame.width
} completion: { (_) in }
}
#objc func gotTap(_ sender: UIButton) -> Void {
guard let pl = scrollView.layer.presentation() else {
return
}
let x = String(format: "%0.2f", pl.bounds.origin.x)
statusLabel.text = "Content Offset X\n\(x)"
}
}