绑定到 SwiftUI Mac 应用程序中的结构属性

Question

我正在 SwiftUI 中构建一个 macOS 单位转换器应用程序。 在下面的示例中，我有一个包含许多文本字段的加速视图。 这些文本字段代表不同的加速度单位。

// AccelerationView.swift

struct AccelerationView: View {

    @State private var accel = Acceleration()
    @EnvironmentObject var formatter: Formatter

    var body: some View {

        VStack(alignment: .leading) {
            Text("Metric").font(.subheadline)
            HStack {
                TextField("kilometer per second squared", value: $accel.kilometerPerSecondSquare, formatter: formatter.numberFormatter).frame(width: 120)
                Text("km/s²").frame(width: 60, alignment: .leading)
            }
            HStack {
                TextField("meter per second squared", value: $accel.meterPerSecondSquare, formatter: formatter.numberFormatter).frame(width: 120)
                Text("m/s²").frame(width: 60, alignment: .leading)
            }
            HStack {
                TextField("millimeter per second squared", value: $accel.millimeterPerSecondSquare, formatter: formatter.numberFormatter).frame(width: 120)
                Text("mm/s²").frame(width: 60, alignment: .leading)
            }
            // and so on ...
        }
        .padding()

    }
}

我想将 HStack 放入自己的文件中以清理视图中的代码。 我在这方面的尝试如下所示：

// UnitTextField.swift

struct UnitTextField: View {

    @State var value: Double = 0.0
    let placeHolder: String
    let label: String
    var fieldWidth: CGFloat = 120
    var labelWidth: CGFloat = 60

    @EnvironmentObject private var formatter: Formatter

    var body: some View {
        HStack {
            TextField(placeHolder, value: $value, formatter: formatter.numberFormatter)
                .frame(width: fieldWidth)
                .multilineTextAlignment(.trailing)
            Text(label)
                .frame(width: labelWidth, alignment: .leading)
        }
    }
}

这不起作用，因为 UnitTextField value没有正确绑定到加速结构。 我正在尝试完成这样的事情，我可以在 AccelerationView 中使用：

// AccelerationView.swift

struct AccelerationView: View {

    @State private var accel = Acceleration()
    @EnvironmentObject var formatter: Formatter

    var body: some View {

        VStack(alignment: .leading) {
            Text("Metric").font(.subheadline)
            UnitTextField(value: $accel.kilometerPerSecondSquare, placeHolder: "kilometer per second squared", label: "km/s²")
            UnitTextField(value: $accel.meterPerSecondSquare, placeHolder: "meter per second squared", label: "m/s²")
            UnitTextField(value: $accel.millimeterPerSecondSquare, placeHolder: "millimeter per second squared", label: "mm/s²")
            // and so on ...
        }
        .padding()
    }
}

关于如何在 SwiftUI 中为 macOS 应用程序正确实现这一点的任何建议？

Answer 1

如果从你要完成的事情（最后一个快照）开始，那么我认为你需要

struct UnitTextField: View {
    @Binding var value: Double

代替

struct UnitTextField: View {
    @State var value: Double = 0.0

Answer 2

binding和environmentObject可能是这样的：

 class MyFormat: Formatter, ObservableObject{
                var numberFormat = NumberFormatter()
            }


            struct UnitTextField: View {

                @Binding var value: Double
                let placeHolder: String
                let label: String
                var fieldWidth: CGFloat = 120
                var labelWidth: CGFloat = 60

                @EnvironmentObject  var formatter: MyFormat

                var body: some View {
                    HStack {
                        TextField(placeHolder, value: $value, formatter: formatter.numberFormat)
                            .frame(width: fieldWidth)
                            .multilineTextAlignment(.trailing)
                        Text(label)
                            .frame(width: labelWidth, alignment: .leading)
                    }
                }
            }

            struct Acceleration{
                var kilometerPerSecondSquare : Double = 0.0
                var meterPerSecondSquare : Double = 1.0
                var millimeterPerSecondSquare : Double = 2.0

            }


            struct AccelerationView: View {

                @State private var accel = Acceleration()
                @EnvironmentObject var formatter: MyFormat

                var body: some View {

                    VStack(alignment: .leading) {
                        Text("Metric").font(.subheadline)
                        UnitTextField(value: $accel.kilometerPerSecondSquare, placeHolder: "kilometer per second squared", label: "km/s²").environmentObject(formatter)
                        UnitTextField(value: $accel.meterPerSecondSquare, placeHolder: "meter per second squared", label: "m/s²").environmentObject(formatter)
                        UnitTextField(value: $accel.millimeterPerSecondSquare, placeHolder: "millimeter per second squared", label: "mm/s²").environmentObject(formatter)
                        // and so on ...
                    }
                    .padding()
                }
            }