ios - SwiftUI 为什么 Picker 上的输入不起作用？

Question

我对 SwiftUI 很陌生，我需要社区的帮助来理解为什么在以下代码中选择任何 Picker 选项似乎都不起作用，要么是不可选择的，因此不会触发任何操作，要么它被选中并且它不会触发任何事情。

非常感谢您让我知道下划线的概念。

德沃

import SwiftUI

struct ContentView: View {
    
    @State private var measureToConvert = ""
    
    @State private var conversionFromMeasure = "km"
    
    @State private var convertedToMeasure = "m"
    
    let measure = ["m", "km", "ft", "yd", "mi"]
    
    
    func convertInMillimeters(input: String, number: String) -> Double {
        
        var value: Double = 0
        
        if let realNumber = Double(number) {
        
        switch input {
        
        case "m":
            
            let conversion = (Double(realNumber) * 1_000)
            
            value = conversion
        
        case "km":
            let conversion = (Double(realNumber) * 1_000_000)
            value = conversion
            
        case "ft":
            let conversion = (Double(realNumber) * 304.8)
            value = conversion
            
        case "yd":
            let conversion = (Double(realNumber) * 914.4)
            return conversion
            
        case "mi":
            let conversion = (Double(realNumber) * 1_609_344)
            value = conversion
        default:
            
            let conversion = -2.0
            
            value = conversion
            }
           
        }
        
        print("value in millimeters is \(value)")
        return value
        

    }



    func convertToNewMeasure(input: String, number: Double) -> Double {
        
        var value: Double = 0
        
        switch input {
        
        case "m" :
            
            let conversion = (number / 1_000)
            
            value = conversion
        
        case "km":
            let conversion = (number / 1_000_000)
            value = conversion
            
        case "ft":
            let conversion = (number / 304.8)
            value = conversion
            
        case "yd":
            let conversion = (number / 914.4)
            return conversion
            
        case "mi":
            let conversion = (number / 1_609_344)
            value = conversion
        
        default:
            
            let conversion = -1.0
            
            value = conversion
            }
           
        
        print("value converted is \(value)")
        return value
        
    }
    
    var inMillimeters : Double {
       return convertInMillimeters(input: conversionFromMeasure, number: measureToConvert)
    }

    var result: Double {
        
        return convertToNewMeasure(input: convertedToMeasure, number: inMillimeters)
    }
    
    
    var body: some View {
        
        NavigationView{
        
        Form{
        
            
            Section(header: Text("Value to convert:")){
            TextField("Enter a measure", text: $measureToConvert).keyboardType(.decimalPad)
            
            }
            
            
            
        Section(header: Text("Select input measure")){
            Picker("From", selection: $conversionFromMeasure) {
                ForEach(0 ..< measure.count){
                    Text("\(self.measure[$0])")
                    
                    
                }
                
            }.pickerStyle(SegmentedPickerStyle())
        }
      
        
        Section(header: Text("Select output measure")){
            Picker("To", selection: $convertedToMeasure) {
                ForEach(0 ..< measure.count) {
                    Text("\(self.measure[$0])")
                    
                }
                
            }.pickerStyle(SegmentedPickerStyle())        }
            
            
        
        
            Section(header: Text("Converted value")){
                Text("\(result, specifier: "%.2f")")
            }
        }
        .navigationBarTitle("Measure Converter")
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}

标签： iosswiftuibindingstatepicker

Answer 1

当使用带有这几个选项的选择器时，使用枚举来存储值非常方便，您还可以使用枚举来存储您的函数并返回您想要的结果。您可以在此处了解有关枚举的更多信息

创建枚举后，使其符合 CaseIterable，这将为您提供所有案例的数组，然后您将在 ForEach 中使用这些案例。

您还给它一个 rawValue，它将作为填充每个选择器选项的内容。很清楚我在那里的代码中做了什么。

 import SwiftUI

struct ContentView: View {
    
    enum Unit: String, CaseIterable {
        case meters = "m"
        case kilometers = "km"
        case feet = "ft"
        case yards = "yd"
        case miles = "mi"
        
    }
    
    @State private var unitSelection: Unit = .meters
    @State private var measureToConvert = ""
    
    @State private var conversionFromMeasure = "km"
    
    @State private var convertedToMeasure = "m"
    
    let measure = ["m", "km", "ft", "yd", "mi"]
    
    
    func convertInMillimeters(input: String, number: String) -> Double {
        
        var value: Double = 0
        
        if let realNumber = Double(number) {
        
        switch input {
        
        case "m":
            
            let conversion = (Double(realNumber) * 1_000)
            
            value = conversion
        
        case "km":
            let conversion = (Double(realNumber) * 1_000_000)
            value = conversion
            
        case "ft":
            let conversion = (Double(realNumber) * 304.8)
            value = conversion
            
        case "yd":
            let conversion = (Double(realNumber) * 914.4)
            return conversion
            
        case "mi":
            let conversion = (Double(realNumber) * 1_609_344)
            value = conversion
        default:
            
            let conversion = -2.0
            
            value = conversion
            }
           
        }
        
        print("value in millimeters is \(value)")
        return value
        

    }



    func convertToNewMeasure(input: String, number: Double) -> Double {
        
        var value: Double = 0
        
        switch input {
        
        case "m" :
            
            let conversion = (number / 1_000)
            
            value = conversion
        
        case "km":
            let conversion = (number / 1_000_000)
            value = conversion
            
        case "ft":
            let conversion = (number / 304.8)
            value = conversion
            
        case "yd":
            let conversion = (number / 914.4)
            return conversion
            
        case "mi":
            let conversion = (number / 1_609_344)
            value = conversion
        
        default:
            
            let conversion = -1.0
            
            value = conversion
            }
           
        
        print("value converted is \(value)")
        return value
        
    }
    
    var inMillimeters : Double {
       return convertInMillimeters(input: conversionFromMeasure, number: measureToConvert)
    }

    var result: Double {
        
        return convertToNewMeasure(input: convertedToMeasure, number: inMillimeters)
    }
    
    
    var body: some View {
        
        NavigationView{
        
        Form{
        
            
            Section(header: Text("Value to convert:")){
            TextField("Enter a measure", text: $measureToConvert).keyboardType(.decimalPad)
            
            }
            
            
            
        Section(header: Text("Select input measure")){
            Picker("From", selection: $unitSelection) {
                ForEach(Unit.allCases, id: \.self){ unit in
                    Text(unit.rawValue)
                    
                    
                }
                
            }.pickerStyle(SegmentedPickerStyle())
        }
      
        
        Section(header: Text("Select output measure")){
            Picker("To", selection: $convertedToMeasure) {
                ForEach(0 ..< measure.count) {
                    Text("\(self.measure[$0])")
                    
                }
                
            }.pickerStyle(SegmentedPickerStyle())        }
            
            
        
        
            Section(header: Text("Converted value")){
                Text("\(result, specifier: "%.2f")")
            }
        }
        .navigationBarTitle("Measure Converter")
        }
    }
}

struct ContentView_Previews: PreviewProvider {
    static var previews: some View {
        ContentView()
    }
}