如何用按钮 increase/decrease 给标签值定价？

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时 priceLabel 增加或减少 quantityLabel 值。（例如 1 个数量是 $15,00 2 个数量是 $30,00）

下面我试过了

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：添加了带有完整代码的 DetailVC 我的数据来自 MainVC table view selected cell to DetailVc class 细节视图控制器：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，您不更新价格标签，在 decreaseQuantity 方法中，您不能使用标签的文本（字符串）并对其进行数学计算。

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。因此，每次更新其中的属性时，它都会创建一个新的结构实例。这样我们就可以在每次有变化时使用 didSet 回调来更新标签。

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
    }
}

如何用按钮 increase/decrease 给标签值定价？

How to increase/decrease price label value with button?

label

ios

swift4.2

定义一个 ViewModel 结构

更新标签