How to Parallax?

Let's see how to create a parallax effect in your app.

First, let's define what parallax is. Parallax scrolling is a popular design technique used to create a scrolling effect by moving multiple layers of content at different speeds. It's an effective way to add visual interest and depth to your app or website. You can achieve a similar effect with UIScrollView. In this blog post, we'll explore how to create a parallax effect using UIScrollView.

To create a parallax effect with UIScrollView, we'll use two parallax sub-views. We will adjust their position based on the scroll position of the UIScrollView.

Step 1: Create the views

First, let's create our views programmatically and set up initial frames/constraints. We can do this in the viewDidLoad() method of our view controller.

class ViewController: UIViewController, UIScrollViewDelegate {

    let scrollView = UIScrollView()
    let contentView = UIView()
    let parallax1View = UIView()
    let parallax2View = UIView()
    let parallax3View = UIView()

    override func viewDidLoad() {
        super.viewDidLoad()

        scrollView.delegate = self
        scrollView.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(scrollView)

        contentView.translatesAutoresizingMaskIntoConstraints = false
        scrollView.addSubview(contentView)

        parallax1View.frame = CGRect(x: 0, y: 0, width: 200, height: 100)
        parallax1View.backgroundColor = .red
        parallax1View.clipsToBounds = true
        parallax1View.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(parallax1View)

        parallax2View.frame = CGRect(x: 100, y: 0, width: 200, height: 100)
        parallax2View.backgroundColor = .yellow
        parallax2View.clipsToBounds = true
        parallax2View.translatesAutoresizingMaskIntoConstraints = false
        contentView.addSubview(parallax2View)

        self.setUpConstraints()
    }

    func setUpConstraints() {
        NSLayoutConstraint.activate([
            // Scroll view
            scrollView.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            scrollView.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            scrollView.topAnchor.constraint(equalTo: view.topAnchor),
            scrollView.bottomAnchor.constraint(equalTo: view.bottomAnchor),

            // Content view
            contentView.leadingAnchor.constraint(equalTo: scrollView.leadingAnchor),
            contentView.trailingAnchor.constraint(equalTo: scrollView.trailingAnchor),
            contentView.topAnchor.constraint(equalTo: scrollView.topAnchor),
            contentView.bottomAnchor.constraint(equalTo: scrollView.bottomAnchor),
            contentView.widthAnchor.constraint(equalTo: scrollView.widthAnchor),
            contentView.heightAnchor.constraint(equalTo: scrollView.heightAnchor, multiplier: 2)
        ])
    }
}

In this code, we create the required views and set up constraints to position and size the views.

Step 2: Adjust parallax sub-view positions

Next, we need to adjust the position of the parallaxImageView based on the scroll position of the UIScrollView. We can do this in the scrollViewDidScroll(_:) method of the UIScrollViewDelegate protocol.

extension ViewController {
    func scrollViewDidScroll(_ scrollView: UIScrollView) {
        let yContentOffest = scrollView.contentOffset.y
        let ySlowerOffset = yContentOffest / 2
        let yFasterOffset = 2 * yContentOffest
        parallax1View.frame.origin.y = -ySlowerOffset
        parallax2View.frame.origin.y = -yFasterOffset
    }
}

In this code, we calculate the vertical offset of the UIScrollView and adjust the position of the parallax view.

Conclusion

In this blog, we learned how to create a very basic parallax effect using UIScrollView. We created two views, set up constraints, and adjusted their position based on the scroll position. Now you can use this technique to create stunning parallax effects in your own apps!