Updating array of objects in Content View SwiftUI

Question

I make an array in ContentView and I can change the context of it when someone dragging the object. In ContentView I have an array nodes.n_array that is an array of Node objects. In ForEach(in ContentView) I try to detect dragging the object and change coordinates of it. It doesn't work.

Node class:

import Foundation
import SwiftUI

class Node: Decodable, ObservableObject {
    enum CodingKeys: CodingKey {
        case id, x, y, text, red, green, blue, shape
    }
    
    
    public let id: Int
    @Published var x: Double
    @Published var y: Double
    public let text: String
    public var red: Double
    public var green: Double
    public var blue: Double
    public var shape: Int
    
    required init(from decoder: Decoder) throws {
        let container = try decoder.container(keyedBy: CodingKeys.self)
        id = try container.decode(Int.self, forKey: .id)
        x = try container.decode(Double.self, forKey: .x)
        y = try container.decode(Double.self, forKey: .y)
        text = try container.decode(String.self, forKey: .text)
        red = try container.decode(Double.self, forKey: .red)
        green = try container.decode(Double.self, forKey: .green)
        blue = try container.decode(Double.self, forKey: .blue)
        shape = try container.decode(Int.self, forKey: .shape)
    }
}
    
extension Node {
    func circle() -> some View {
        Circle()
            .fill(Color(red: red, green: green, blue: blue))
            .frame(width: 64, height: 64, alignment: .center)
            .position(x: x, y: y)
    }
    
    func square() -> some View {
        Rectangle()
            .fill(Color(red: red, green: green, blue: blue))
            .frame(width: 64, height: 64, alignment: .center)
            .position(x: x, y: y)
    }
    
    @ViewBuilder func drawShape() -> some View {
        switch shape{
        case 1: circle()
        case 2: square()
            default: Text("Failed")
        }
    }
    
    func label() -> some View {
        return Text(text)
            .font(.system(size: 30))
            .bold()
            .position(x: x, y: y)
            .foregroundColor(Color(red: 0.25, green: 0.25, blue: 0.25))
    }
}

Nodes class:

import Foundation

class Nodes: ObservableObject {
   @Published var n_array: [Node]

    init() {
        let url = Bundle.main.url(forResource: "nodes", withExtension: "json")!
        let data = try! Data(contentsOf: url)
        n_array = try! JSONDecoder().decode([Node].self, from: data)
    }
}

Content View:

import SwiftUI

struct ContentView: View {
    @ObservedObject var nodes = Nodes()
    
    var body: some View {
        
        ZStack {
            
            ForEach(0..<nodes.n_array.count) { index in
                nodes.n_array[index].drawShape()
                    .gesture(DragGesture()
                        .onChanged { value in
                            nodes.n_array[index].x = value.translation.width
                            nodes.n_array[index].y = value.translation.height
                        }
                        .onEnded { value in
                            
                        }
                    )
                nodes.n_array[index].label()
            }
        }
    }
}

jnpdx · Accepted Answer · 2021-12-27 22:14:39Z

0

Nested ObservableObjects don't work in SwiftUI unless you manually propagate the state back up to the parent object by calling objectWillChange.

Generally, the standard route is to use a struct for your model and then have the array managed by the ObservableObject parent.

If you change your model to the following, you'll see the drag start to update:

struct Node: Decodable {
    public let id: Int
    var x: Double
    var y: Double
    public let text: String
    public var red: Double
    public var green: Double
    public var blue: Double
    public var shape: Int
}

Note: you'll also need a little more logic for your dragging, but that's beyond the direct scope of this question -- you'll see the item jump at the beginning of the drag because you need to store the initial translation

answered Dec 27, 2021 at 22:14

jnpdx

53.3k7 gold badges91 silver badges123 bronze badges

Sign up to request clarification or add additional context in comments.

Collectives™ on Stack Overflow

Updating array of objects in Content View SwiftUI

1 Answer 1

Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

Comments

Your Answer

Sign up or log in

Post as a guest

Related