ios - SwiftUI ForEach index out of range error when removing row

Question

I have a ForEach block and a Stepper embedded in a List view. The contents of the List view's first section is as follows:

ForEach(record.nodes.indices, id: .self) { index in
    HStack {
        TextField("X", text: self.$record.nodes[index].xString)
        Spacer()
        Divider()
        TextField("Y", text: self.$record.nodes[index].yString)
        Spacer()
    }
}
Stepper("± node", onIncrement: {
    self.record.nodes.append(Node(x: 0, y: 0))
}, onDecrement: {
    self.record.nodes.removeLast()
})

The issue I am facing is that upon calling self.record.nodes.removeLast(), the application crashes with an Index out of range error. I've been trying to solve this for hours, but to no avail.

I originally used onDelete, however that produced the same issue.

The project can be found at https://github.com/jacobcxdev/Timekeeper, with this error happening in RecordDetailView.swift.

Answer 1

Problem Description

The index out of range error occurs because init(_ data: Range<Int>, content: @escaping (Int) -> Content) initializer of ForEach does not allow us to modify the array dynamically. For that, we need to use init(_ data: Data, content: @escaping (Data.Element) -> Content) initializer as @Asperi explained in the comment. However, it does not work either in this situation, where bindings are nested, as @JacobCXDev clarified in the reply.

Workaround (I found a solution, see below)

Use custom bindings and an additional state. The custom bindings solve the issue of ForEach over nested bindings. On top of that, you need to modify a state after every touch on the custom binding to re-render the screen. The following is a simplified (untested) code sample.

@State private var xString: String

---

ForEach(record.nodes) { node in
    let xStringBinding = Binding(
        get: { node.xString },
        set: {
            node.xString = $0
            self.xString = $0
        }
    )
    TextField("X", text: xStringBinding)
}

Solution (added on July 10, 2020)

Just define a view struct for the children like the following.

ForEach(record.nodes) { node in
    NodeView(node: node)
}

---

struct NodeView: View {
    @ObservedObject var node: Node

    var body: some View {
        TextField("X", text: self.$node.xString)
    }
}

class Node: ObservableObject, Identifiable {
    @Published var xString: String
    let id: String = UUID().uuidString

    init(xString: String) {
        self.xString = xString
    }
}