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SOLVED: How do I get my View to update when my data changes

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Hi, I am new to swiftui, trying to make a chess app that shows a board 8x8 Rectangles. Chess position is given as a dictionary with each square as key a1-8, b1-8...h1-h8 and a letter describing the piece on that square. The dictionary needs to change as moves are made and the board view should update.

But I cannot see how to do it. Here is my view (only one line etc shwon for brevity)

import SwiftUI

struct BoardView: View {

    // Sizes
    private let squareSize: CGFloat = 65
    private let labelSize: CGFloat = 22

    // Squares on the chess board
    private var a1 = Rectangle(), a2 = Rectangle(), a3 = Rectangle(), a4 = Rectangle()
    ... others for rest of the board

    // Controller
    @ObservedObject var boardController: BoardController

    init(boardController: BoardController) {
        self.boardController = boardController

    // Chess piece overlay
    @ViewBuilder func pieceOverlay(square: String) -> some View {

        if $boardController.position[square] == "K" {
        } else if boardController.position[square] == "Q" {
        } else if boardController.position[square] == "R" {
        } else if boardController.position[square] == "B" {
        } else if boardController.position[square] == "N" {
        } else if boardController.position[square] == "P" {
        } else if boardController.position[square] == "k" {
        } else if boardController.position[square] == "q" {
        } else if boardController.position[square] == "r" {
        } else if boardController.position[square] == "b" {
        } else if boardController.position[square] == "n" {
        } else if boardController.position[square] == "p" {

    var body: some View {
        VStack(alignment: .leading, spacing: 0) {
            HStack(alignment: .center, spacing: 0) {
                Text("8").bold().font(.system(size: labelSize)).frame(width: squareSize, height: squareSize)
                a8.fill(boardController.whiteColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "a8")}
                b8.fill(boardController.blackColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "b8")}
                c8.fill(boardController.whiteColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "c8")}
                d8.fill(boardController.blackColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "d8")}
                e8.fill(boardController.whiteColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "e8")}
                f8.fill(boardController.blackColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "f8")}
                g8.fill(boardController.whiteColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "g8")}
                h8.fill(boardController.blackColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "h8")}
            ... more rows
            HStack(alignment: .center, spacing: 0) {
                Text("1").bold().font(.system(size: labelSize)).frame(width: squareSize, height: squareSize)
                a1.fill(boardController.blackColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "a1")}
                b1.fill(boardController.whiteColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "b1")}
                c1.fill(boardController.blackColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "c1")}
                d1.fill(boardController.whiteColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "d1")}
                e1.fill(boardController.blackColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "e1")}
                f1.fill(boardController.whiteColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "f1")}
                g1.fill(boardController.blackColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "g1")}
                h1.fill(boardController.whiteColor).frame(width: squareSize, height: squareSize).overlay{pieceOverlay(square: "h1")}


I used a controller as various parts of UI will change the position (toolbar buttons, menuitems etc):

import Foundation
import SwiftUI

class BoardController: ObservableObject {

    // Piece position
    @Published var position: Position

    // Board colors
    @Published var whiteColor: Color = .white
    @Published var blackColor: Color = .green

    init() {
        self.position = Position(Position.startingPosition)

    func clearBoard() -> Void {
        position = Position()

    func setupBoard() -> Void {
        position = Position(Position.startingPosition)

In func pieceOverlay if I use a leading $ then I get a compile error:

    if $boardController.position[square] == "K" {

"Referencing subscript 'subscript(_:)' on 'Binding' requires that 'Position' conform to 'MutableCollection'"

If I don't use the $ then code compiles but then when I update the controller's position dictionary the view does not change.

I am confused around when I need @State, @Binding, @StateModel or whether I don't need any of them. Any hwelp would be appreciated. Sorry for the length of my question



@Quartz64 has an extraordinary request:

I am confused around when I need @State, @Binding, @StateModel
or whether I don't need any of them. Any hwelp help would be appreciated.

@twoStraws produced a high-quality twenty-three minute video explaining this. I cannot explain in a forum post what he illustrates brilliantly in a twenty-three minute video.

His video literally starts with "I am going to answer one of the most common questions people have when using SwiftUI..."

See -> Dear Quartz64...

Also, are you trying to learn on your own? I sense you are guessing at how to assemble these parts, rather than following a plan? True?

Some of your code is, uh, ummmm, rather beginner-ish. For instance, you seem to build your board using brute-force design. SwiftUI is very modular, and could help simplify your design immensely.

@twoStraws has a terrific course titled 100 Days of SwiftUI. I think you'd learn a lot from following his course. Learning lessons on sub-views, looping, encapsulation, and the like. Give it a shot! Your chess program will be much easier to code if you care to follow along.

Keep Coding

Good luck!


I see you use an @ObservedObject for the board controller.

@ObservedObject var boardController: BoardController

Do you have a @StateObject for the board controller in another view that you pass to the board view? If not, you should use @StateObject for the board controller.

@StateObject var boardController: BoardController

When you use classes for your app's data, the view that owns the object should use @StateObject. If you pass that object to other views, those views should use @ObservedObject.

When you use structs for your app's data, the view that owns the object should use @State. If you pass that object to other views, those views should use @Binding.


Thank you all, very helpful


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