How to dismiss PKToolPicker when view disappears in SwiftUI? - swiftui

Question

I'm trying to wrap PKCanvasView as a SwiftUI view called CanvasView. I'd like to be able to toggle the whole canvas on top of another view. When the CanvasView appears, I'd like the PKToolPicker to appear. When it disappears, I'd like the PKToolPicker to disappear.
I've found a few similar approaches on here but they only involve showing the picker or toggling the picker with a button; I'd like the picker visibility to be tied to the view visibility.
In the below example you can see that you can toggle the canvas, but once the tool picker is visible, it stays visible.
Here's my CanvasView:
import SwiftUI
import PencilKit
struct CanvasView: UIViewRepresentable {
class Coordinator: NSObject, PKCanvasViewDelegate {
var canvasView: Binding<PKCanvasView>
let onChange: () -> Void
init(canvasView: Binding<PKCanvasView>, onChange: #escaping () -> Void) {
self.canvasView = canvasView
self.onChange = onChange
}
func canvasViewDrawingDidChange(_ canvasView: PKCanvasView) {
if canvasView.drawing.bounds.isEmpty == false {
onChange()
}
}
}
#Binding var canvasView: PKCanvasView
#Binding var toolPickerIsActive: Bool
private let toolPicker = PKToolPicker()
let onChange: () -> Void
func makeUIView(context: Context) -> PKCanvasView {
canvasView.backgroundColor = .clear
canvasView.isOpaque = true
canvasView.delegate = context.coordinator
showToolPicker()
return canvasView
}
func updateUIView(_ uiView: PKCanvasView, context: Context) {
toolPicker.setVisible(toolPickerIsActive, forFirstResponder: uiView)
}
func showToolPicker() {
toolPicker.setVisible(true, forFirstResponder: canvasView)
toolPicker.addObserver(canvasView)
canvasView.becomeFirstResponder()
}
func makeCoordinator() -> Coordinator {
Coordinator(canvasView: $canvasView, onChange: onChange)
}
}
And an example ContentView:
struct ContentView: View {
#State private var canvasView = PKCanvasView()
#State private var toolPickerIsActive = false
#State private var canvasIsVisible = false
var body: some View {
ZStack {
if canvasIsVisible {
CanvasView(canvasView: $canvasView,
toolPickerIsActive: $toolPickerIsActive,
onChange: canvasDidChange)
.onAppear { toolPickerIsActive = true }
.onDisappear { toolPickerIsActive = false }
}
Button(action: {
canvasIsVisible.toggle()
}, label: {
Text("Toggle canvas view")
})
}
}
private func canvasDidChange() {
// Do something with updated canvas.
}
}
Any guidance would be much appreciated!

Answer 1

In your scenario the CanvasView is destroyed on disappear, so SwiftUI rendering engine just not update it on any state change (as it see that no needs for that).
The possible solution for this use-case is to hide picker on coordinator deinit (because it is destroyed with owner view).
Here is a demo. Tested with Xcode 12.4 / iOS 14.4
struct CanvasView: UIViewRepresentable {
class Coordinator: NSObject, PKCanvasViewDelegate {
var canvasView: Binding<PKCanvasView>
let onChange: () -> Void
private let toolPicker: PKToolPicker
deinit { // << here !!
toolPicker.setVisible(false, forFirstResponder: canvasView.wrappedValue)
toolPicker.removeObserver(canvasView.wrappedValue)
}
init(canvasView: Binding<PKCanvasView>, toolPicker: PKToolPicker, onChange: #escaping () -> Void) {
self.canvasView = canvasView
self.onChange = onChange
self.toolPicker = toolPicker
}
func canvasViewDrawingDidChange(_ canvasView: PKCanvasView) {
if canvasView.drawing.bounds.isEmpty == false {
onChange()
}
}
}
#Binding var canvasView: PKCanvasView
#Binding var toolPickerIsActive: Bool
private let toolPicker = PKToolPicker()
let onChange: () -> Void
func makeUIView(context: Context) -> PKCanvasView {
canvasView.backgroundColor = .clear
canvasView.isOpaque = true
canvasView.delegate = context.coordinator
showToolPicker()
return canvasView
}
func updateUIView(_ uiView: PKCanvasView, context: Context) {
toolPicker.setVisible(toolPickerIsActive, forFirstResponder: uiView)
}
func showToolPicker() {
toolPicker.setVisible(true, forFirstResponder: canvasView)
toolPicker.addObserver(canvasView)
canvasView.becomeFirstResponder()
}
func makeCoordinator() -> Coordinator {
Coordinator(canvasView: $canvasView, toolPicker: toolPicker, onChange: onChange)
}
}
struct ContentView: View {
#State private var canvasView = PKCanvasView()
#State private var toolPickerIsActive = false
#State private var canvasIsVisible = false
var body: some View {
ZStack {
if canvasIsVisible {
CanvasView(canvasView: $canvasView,
toolPickerIsActive: $toolPickerIsActive,
onChange: canvasDidChange)
.onAppear { toolPickerIsActive = true }
// .onDisappear { toolPickerIsActive = false }
}
Button(action: {
canvasIsVisible.toggle()
}, label: {
Text("Toggle canvas view")
})
}
}
private func canvasDidChange() {
// Do something with updated canvas.
}
}
Note: there might be redesign of ownership, so toolPicker will live only within coordinator, but it does not change idea, and is up to you.