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Advanced ScrollView

Advanced ScrollView creates a bridge between UIScrollView and NSScrollView and SwiftUI views.

What makes this scroll view "advanced"? You have full access to UIScrollView and NSScrollView APIs. It is harder to use, but you can build all kinds of interactions, like pinch to zoom at precise point, scroll with a given offset, infinite canvas, etc.

import SwiftUI
import AdvancedScrollView


struct ScrollableImage: View {

    let image: Image

    var body: some View {
        AdvancedScrollView { _ in
            image
        }
    }
}

See the showcase app for some ideas: ShapeEdit.

Magnification

You can configure magnification behaviour using Magnification struct.

let magnification = Magnification(range: 1.0...4.0, initialValue: 1.0, isRelative: true)

AdvancedScrollView(magnification: magnification) { _ in
    image
}

range and initialValue allows to configure magnification range and initial magnification respectfully. isRelative defines if magnification must be calculated relative to the view's frame. I.e. content magnified to fit in the view.

Proxy

Similarly to ScrollView and ScrollViewReader combination, AdvancedScrollView takes ViewBuilder closure with a single AdvancedScrollViewProxy argument that provides access to common properties and methods of the underlying scroll view.

The names are self-explanatory and while this documentation is in development please refer to UIScrollView/NSScrollView APIs.

func scrollTo(_ rect: CGRect, animated: Bool)

var contentOffset: CGPoint { get set }

var contentSize: CGSize { get }

var contentInset: EdgeInsets { get set }

var visibleRect: CGRect { get }

var scrollerInsets: EdgeInsets { get }

var magnification: CGFloat { get }

var isLiveMagnify: Bool { get }

Events and Gestures

AdvancedScrollView won't alter event handling so in most cases you can expect SwiftUI gestures to work as is. But, underlying NSScrollView, when magnified, won't correctly translate points from its coordinate system to SwiftUI views. Good news is that UIScrollView correctly translates coordinates.

As a solution to this problem AdvancedScrollView provides onTapContentGesture and onDragContentGesture gestures. This replicates onTap and onDrag view modifiers.

Downside is that this are event handlers are attached to the scroll view itself, so you need to determine which subview should handle an event.

Benefit is that onDragContentGesture will manage state for you and even autoscroll content when needed.

If you're building iOS only app, not using magnification, or do not need to handle gestures at a specific location, using SwiftUI gestures with AdvancedScrollView should cover your case.

If you happen to know how to make NSScrollView translate coordinates correctly, please reach out.