想在方程式中使用@Binding 变量

Question

struct FinanceOutput: View {
@Binding var price: Double
@Binding var down: Double
@Binding var apr: Double  
private var rate: Double = 0.0     
init(price: Binding<Double>, down:Binding<Double>, apr:Binding<Double>, of rate: Double ) {                
  self._price = price
  self._down = down
  self._apr = apr          
 self.rate = rate       
}

以上是我的代码，我确实在另一个视图中正确定义了@Binding 变量——使用@State。

我要做的是在等式中使用“率”来定义“apr/12”。我想我以前在早期版本的 Xcode 中解决了这个问题，但现在我得到的只是：“不能在属性初始化程序中使用实例成员 'apr'；属性初始化程序在 'self' 可用之前运行。” 我知道我正在使用 Binding 类型，但即使我使用 Double() 更改类型，我仍然会收到错误。任何帮助，将不胜感激。

Answer 1

您似乎正试图在 init() 完成之前访问您的结构中的一个属性，例如：

struct FinanceOutput: View {
    @Binding var price: Double
    @Binding var down: Double
    @Binding var apr: Double

    private var rate: Double = 0.0

    init(price: Binding<Double>, down: Binding<Double>, apr: Binding<Double>, of rate: Double) {
        self._price = price
        self._down = down
        self._apr = apr
        self.rate = rate
    }

    apr = rate // error: Cannot use instance member 'apr' within property initializer; property initializers run before 'self' is available.

    var body: some View {
        Text("\(apr/rate)")
    }
}

您可以从正文中访问“速率”属性，例如：

let input = Input(price: 10.0, down: 10.0, apr: 10.0)

struct FinanceOutput: View {
    @Binding var price: Double
    @Binding var down: Double
    @Binding var apr: Double

    private var rate: Double = 0.0

    init(price: Binding<Double>, down: Binding<Double>, apr: Binding<Double>, of rate: Double) {
        self._price = price
        self._down = down
        self._apr = apr
        self.rate = rate
    }

    var body: some View {
        Text("\(apr/rate)") // shows apr/rate properly
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        FinanceOutput(price: input.$price, down: input.$down, apr: input.$apr, of: 12.0)
    }
}

struct Input: View {
    @State var price: Double
    @State var down: Double
    @State var apr: Double

    var body: some View {
        Text("\(price), \(down), \(apr)")
    }
}