EnvironmentObject not found for child Shape in SwiftUI - swiftui

Question

I am encountering the following SwiftUI error with #EnvironmentObject when used with a custom Shape, :
Fatal error: No ObservableObject of type MyObject found. A View.environmentObject(_:) for MyObject may be missing as an ancestor of this view.: file SwiftUI, line 0
It only happens when I use any Shape method that returns a new copy of the instance like stroke().
Here is a Swift playground example to reproduce:
import SwiftUI
import PlaygroundSupport
class MyObject: ObservableObject {
#Published var size: Int = 100
}
struct MyShape: Shape {
#EnvironmentObject var envObj: MyObject
func path(in rect: CGRect) -> Path {
let path = Path { path in
path.addRect(CGRect(x: 0, y: 0,
width: envObj.size, height: envObj.size))
}
return path
}
}
struct MyView: View {
var body: some View {
MyShape().stroke(Color.red) // FAIL: no ObservableObject found
// MyShape() // OK: it works
}
}
let view = MyView().environmentObject(MyObject())
PlaygroundPage.current.setLiveView(view)
As it looks like environment field is not copied, I've also tried to do it explicitly like this:
struct MyView: View {
#EnvironmentObject var envObj: MyObject
var body: some View {
MyShape().stroke(Color.red).environmentObject(self.envObj)
}
}
It still fails. As a SwiftUI beginner, I don't know whether this is the expected behavior, not inheriting the view hierarchy environment, and how to handle it - other than not using the environment.
Any idea?

Answer 1

The problem actually is that .stroke is called right after constructor, so before environmentObject injected (you can test that it works if you comment out stroke). But .stroke cannot be added after environment object injected, because .stroke is Shape-only modifier.
The solution is to inject dependency during construction as below. Tested with Xcode 11.4 / iOS 13.4
struct MyShape: Shape {
#ObservedObject var envObj: MyObject
...
}
struct MyView: View {
#EnvironmentObject var envObj: MyObject
var body: some View {
MyShape(envObj: self.envObj).stroke(Color.red)
}
}