I'm trying to handle drag gestures entering into a SwiftUI view. However, DragGesture only fires (updates, changes) when the event originated in the view itself.
I could certainly think of various workarounds, yet I wanted to double-check if there is an easy/intended way to do this.
I'm looking for something similar to a UIKit touchDragEnter, or JavaScript ondragenter.
I ended up intercepting touches in an overlay view, then highlight items when touch location is contained in its bounds. I tried both onDrop and using UIKit gestures/actions, but none of them came without drawbacks. So I opted to implement George's comment above instead.
I incorporated a model object where I store the frames on every update, so highlight effect can adopt dynamically. It makes the solution animation proof, while picker also can be displayed anywhere on the screen.
import SwiftUI
class Model: ObservableObject {
let coordinateSpace = "CoordinateSpace"
@Published var isDragged = false
@Published var highlightedNumber: Int? = nil
@Published var selectedNumber: Int? = nil
/// Frames for individual picker items (from their respective `GeometryReader`).
private var framesForNumbers: [Int: CGRect] = [:]
func update(frame: CGRect, for number: Int) {
framesForNumbers[number] = frame
}
/// Updates `highlightedNumber` according drag location.
func update(dragLocation: CGPoint) {
// Lookup if any frame contains drag location.
for (eachNumber, eachFrame) in framesForNumbers {
if eachFrame.contains(dragLocation) {
// Publish.
self.highlightedNumber = eachNumber
return
}
}
// Reset otherwise.
self.highlightedNumber = nil
}
/// Updates `highlightedNumber` and `selectedNumber` according drop location.
func update(isDragged: Bool) {
// Publish.
self.isDragged = isDragged
if isDragged == false,
let highlightedNumber = self.highlightedNumber {
// Publish.
self.selectedNumber = highlightedNumber
self.highlightedNumber = nil
}
}
}
struct ContentView: View {
@StateObject var model = Model()
var body: some View {
ZStack {
TouchesView(model: model, isDragged: $model.isDragged)
CanvasView(number: $model.selectedNumber)
.allowsHitTesting(false)
PickerView(model: model, highlightedNumber: $model.highlightedNumber)
.allowsHitTesting(false)
}
.ignoresSafeArea()
}
}
/// Handles drag interactions and updates model accordingly.
struct TouchesView: View {
var model: Model
@Binding var isDragged: Bool
var body: some View {
Rectangle()
.foregroundColor(isDragged ? .orange : .yellow)
.coordinateSpace(name: model.coordinateSpace)
.gesture(
DragGesture(minimumDistance: 0)
.onChanged { value in
model.update(dragLocation: value.location)
model.update(isDragged: true)
}
.onEnded { state in
model.update(dragLocation: state.location)
model.update(isDragged: false)
}
)
}
}
/// Shows the selected number.
struct CanvasView: View {
@Binding var number: Int?
var body: some View {
VStack {
Text(number.string)
.font(.system(size: 100, weight: .bold))
.foregroundColor(.white)
.offset(y: -50)
}
}
}
/// Displays a picker to select number items from.
struct PickerView: View {
var model: Model
@Binding var highlightedNumber: Int?
var body: some View {
HStack(spacing: 5) {
PickerItemView(number: 1, model: model, highlightedNumber: $highlightedNumber)
PickerItemView(number: 2, model: model, highlightedNumber: $highlightedNumber)
PickerItemView(number: 3, model: model, highlightedNumber: $highlightedNumber)
}
.opacity(model.isDragged ? 1 : 0)
.scaleEffect(model.isDragged ? 1 : 0.5, anchor: .top)
.blur(radius: model.isDragged ? 0 : 10)
.animation(.spring(response: 0.15, dampingFraction: 0.4, blendDuration: 0.5))
}
}
/// Shows a number item (also highlights it when `highlightedNumber` matches).
struct PickerItemView: View {
let number: Int
var model: Model
@Binding var highlightedNumber: Int?
var body: some View {
Text(String(number))
.font(.system(size: 25, weight: .bold))
.foregroundColor(isHighlighted ? .orange : .white)
.frame(width: 50, height: 50)
.background(isHighlighted ? Color.white : Color.orange)
.cornerRadius(25)
.overlay(
RoundedRectangle(cornerRadius: 25)
.stroke(Color.white, lineWidth: 2)
)
.overlay(GeometryReader { geometry -> Color in
self.model.update(
frame: geometry.frame(in: .named(self.model.coordinateSpace)),
for: self.number
)
return Color.clear
})
.animation(.none)
}
}
extension PickerItemView {
var isHighlighted: Bool {
self.highlightedNumber == self.number
}
}
fileprivate extension Optional where Wrapped == Int {
var string: String {
if let number = self {
return String(number)
} else {
return ""
}
}
}
struct PrototypeView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
}
}
Only thing I dislike about this is that this method is esentially the same I did 15 years ago in a Flash app. I was hoping to something less "manual".