如何使用按钮增加/减少价格标签值？

Question

我有两个标签。第一个是quantityLabel，第二个是priceLabel。当我点击增加或减少按钮priceLabel 增加或减少quantityLabel 值。 （例如 1 个数量为 $15,00 2 个数量为 $30,00）

我在下面尝试过

var quantity = 1
var updateFoodPrice: Double? {
    didSet {
        foodPrice.text = "\(Double(quantity) * updateFoodPrice!)"
    }
}

@IBAction func addQuantity(_ sender: Any) {
    if quantity < 30 {
        quantity += 1
        foodQuantity.text = String(quantity)

    }

}

@IBAction func decreasedQuantity(_ sender: Any) {
    if quantity > 0 {
        quantity -= 1
        foodQuantity.text = String(quantity)
        foodPrice.text? *= "\(quantity)"
    }
}

编辑：添加了包含完整代码的 DetailVC 我的数据来自 MainVC 表视图选定的单元格到 DetailVc 类 DetailViewController: UIViewController {

@IBOutlet weak var foodTitle: UILabel!
@IBOutlet weak var foodSubTitle: UILabel!
@IBOutlet weak var foodPrice: UILabel!
@IBOutlet weak var drinkPicker: UITextField!
@IBOutlet weak var foodQuantity: UILabel!


var drinkPickerView = UIPickerView()
var selectDrinkType: [String] = []
var detailFoodName = ""
var detailFoodPrice = 0.0

var searchFoods: [String]!
var priceFood: [Double]!

let foods = Food(name: ["Hamburger big mac",
                           "Patates",
                           "Whopper",
                           "Steakhouse"], price: [15.0, 20.0, 25.0, 30.0])
let food: Food! = nil

var foodPriceCount = FoodPriceCount(quantity: 1, foodPrice: 15.0) {

    didSet {
        foodQuantity.text = "\(foodPriceCount.quantity)"
        foodPrice.text = "\(Double(foodPriceCount.quantity) * foodPriceCount.foodPrice)TL"

    }
  }

@IBAction func addQuantity(_ sender: Any) {
    if foodPriceCount.quantity < 30 {
        foodPriceCount.quantity += 1
    }
  }

@IBAction func decreasedQuantity(_ sender: Any) {
    if foodPriceCount.quantity > 0 {
        foodPriceCount.quantity -= 1
    }
    } 

viewDidLoad()

   override func viewDidLoad() {
    super.viewDidLoad()

    foodQuantity.text = "1"

    searchFoods = foods.name
    priceFood = foods.price

    foodTitle.text = detailFoodName
    foodPrice.text = String(detailFoodPrice)

Answer 1

在addQuantity 方法中，您不会更新价格标签，而在decreaseQuantity 方法中，您不能使用标签的文本（字符串）并对其进行数学运算。

我建议使用一个包含两个值的结构。使用结构的好处是它是不可变的。所以每次你更新其中的一个属性时，它都会创建一个新的结构实例。这样我们就可以使用didSet 回调在每次发生变化时更新标签。

定义一个 ViewModel 结构

struct ViewModel {
    var quantity: Int
    var foodPrice: Double
}

更新标签

var viewModel = ViewModel(quantity: 1, foodPrice: 10) {
    didSet {
        foodQuantityLabel.text = "\(viewModel.quantity)"
        foodPriceLabel.text = "\(Double(viewModel.quantity) * viewModel.foodPrice)"
    }
}

@IBAction func addQuantity(_ sender: Any) {
    if viewModel.quantity < 30 {
        viewModel.quantity += 1
    }
}

@IBAction func decreasedQuantity(_ sender: Any) {
    if viewModel.quantity > 0 {
        viewModel.quantity -= 1
    }
}