private func setup() {

        var stacks = [UIStackView]()

        for r in 0..<6 {
            let stack = UIStackView()
            stack.distribution = .fillProportionally
            self.addSubview(stack)

            stack.translatesAutoresizingMaskIntoConstraints = false
            stack.leadingAnchor.constraint(equalTo: self.leadingAnchor, constant: 20).isActive = true
            stack.trailingAnchor.constraint(equalTo: self.trailingAnchor, constant: -20).isActive = true
            stack.heightAnchor.constraint(equalToConstant: 50).isActive = true

            if stacks.isEmpty {
                stack.topAnchor.constraint(equalTo: self.topAnchor, constant: 100).isActive = true
            } else {
                stack.topAnchor.constraint(equalTo: stacks.last!.bottomAnchor, constant: 20).isActive = true
            }

            var rowPieces = [Piece]()

            for c in 0..<7 {
                let piece = Piece(frame: CGRect(x: 0, y: 0, width: 50, height: 50))
                piece.row = r
                piece.column = c
                piece.addTarget(self, action: #selector(selectedPiece(_:)), for: .touchUpInside)
                rowPieces.append(piece)
                stack.addArrangedSubview(piece)
            }
            gridPieces.append(rowPieces)
            stacks.append(stack)
        }
        createResetButton()
    }