SwiftUI @Published var inconsistently updating views

Question

Created Feb ’22

Replies 3

Boosts 0

Participants 2

I am working on a simple Reversi app built using SwiftUI. Recently I was updating my app and noticed a bug with the UI not updating to match the game state.

Here is a screenshot of an in-progress game:

Here is a screenshot of the board after I press the undo button:

In the second screenshot, the middle-rightmost white piece should be black. The views that display the pieces depend on a game environmentObject:

class Game: ObservableObject {
    @Published var board = Board()
    @Published var times = GameState.times
    var pieces: [Piece] {
        board.pieces.filter({ $0 != nil}) as! [Piece]
    }
}

I only ever initialize a Game() object once, in the root of my app:

@main
struct DuelingDisksApp: App {
	@StateObject private var game = Game()

	var body: some Scene {
		WindowGroup {
			GamesView()
				.environmentObject(game)
		}
	}
}

Later, I use the game in a view which displays the correct piece (if any) for a square:

struct SquareView: View {
    @EnvironmentObject private var game: Game
    let column: Int
    let row: Int
    
    var body: some View {
        let square = Square(column: column, row: row)
        let animation: Animation = .linear(duration: 0.3)
        ZStack {
            Button {
            } label: {
                Text("")
            }
            .disabled(game.board.gameOver)
            
            if let piece = game.board.pieces[square] {
                PieceView(isLight: piece.isLight)
                    .frame(width: boardLength / 16, height: boardLength / 16)
                    .transition(.opacity.animation(animation))
                    .animation(animation, value: game.board)
                    .zIndex(1)
            }
        }
    }
}

Any ideas as to why only some of the views are getting updated? One thing I tried was to replace @Published var board = Board() in the Game class with:

@Published var board = Board() {
	willSet {
		objectWillChange.send()
	}
}

This fixed the issue. My understanding was that this is equivalent to @Published var board = Board(). If anyone has any ideas on why this issue might be occurring and why adding the objectWillChange fixes it, I would love to know. From all my testing I have been wondering if it is a bug with SwiftUI but want to make sure that I'm not just doing something incorrectly.

Thanks for any help!

Boost

Answer 1

Claude31 OP

Feb ’22

Could you show how you call SquareView ?

0

Answer 2

Sammcb OP

Feb ’22

SquareView is called here:

// SizeRange is 1...8
struct BoardView: View {    
    var body: some View {
        VStack(alignment: .center, spacing: 0) {
            ForEach(SizeRange.reversed(), id: \.self) { row in
                HStack(spacing: 0) {
                    ForEach(SizeRange, id: \.self) { column in
                        SquareView(column: column, row: row)
                    }
                }
            }
        }
    }
}

0

Answer 3

Sammcb OP

Feb ’22

SquareView is called here (posted in answer as well in case it's more readable):

struct BoardView: View {    
    var body: some View {
        VStack(alignment: .center, spacing: 0) {
            ForEach(SizeRange.reversed(), id: \.self) { row in
                HStack(spacing: 0) {
                    ForEach(SizeRange, id: \.self) { column in
                        SquareView(column: column, row: row)
                    }
                }
            }
        }
    }
}

0