SwiftUI:更改数据源时Picker无法正确更新 [英] SwiftUI : Picker does not update correctly when changing datasource

问题描述

我刚刚开始学习SwiftUI并被卡在某个地方！

I have just started learning SwiftUI and got stuck somewhere!

我试图在更改另一个细分的值时更改细分样式的选择器数据源.但是不知何故，它无法正常工作！否则我可能编码有误.有人可以找出答案吗?

I am trying to change segment styled picker datasource when changing value of another segment. But somehow it is not working as expected! Or else I might have coded something wrong. Can anyone figure it out please?

这是我的代码:

import SwiftUI

struct ContentView: View {    

@State var selectedType = 0
@State var inputUnit = 0
@State var outputUnit = 1

let arrTypes = ["Temperature", "Length"]

var arrData: [String] {
    switch self.selectedType {
    case 0:
        return ["Celsius", "Fahrenheit", "Kelvin"] //Temperature
    case 1:
        return ["meters", "kilometers", "feet", "yards", "miles"] //Length        
    default:
        return ["Celsius", "Fahrenheit", "Kelvin"]
    }        
}


var body: some View {
    NavigationView{
        Form
        {
            Section(header: Text("Choose type"))
            {
                Picker("Convert", selection: $selectedType) {
                    ForEach(0 ..< 2, id: \.self)
                    { i in
                        Text(self.arrTypes[i])
                    }
                }
                .pickerStyle(SegmentedPickerStyle())
            }

            Section(header: Text("From"))
            {
                Picker("", selection: $inputUnit) {
                    ForEach(0 ..< arrData.count, id: \.self)
                    {
                        Text(self.arrData[$0])
                    }
                }
                .pickerStyle(SegmentedPickerStyle())                    
            }

            Section(header: Text("To"))
            {
                Picker("", selection: $outputUnit) {
                    ForEach(0 ..< arrData.count, id: \.self)
                    {
                        Text(self.arrData[$0])
                    }
                }
                .pickerStyle(SegmentedPickerStyle())
            }                

        }
    }
}
}

当我将段从Length更改回Temperature时，它将以某种方式合并数组.我尝试调试并打印日志中的arrData计数，然后它显示正确的结果，但未更新UI！

When I change segment from Length back to Temperature it merges the array somehow. I tried to debug and print the arrData count in log, then it prints correct result but not updating the UI!

默认情况下选择的第一个细分:

更改细分:

将细分重新更改为第一个

任何帮助或建议，将不胜感激.

Any help or suggestion would greatly be appreciated.

推荐答案

Nick Polychronakis在此fork中解决了它: https://github.com/nickpolychronakis/100DaysOfSwiftUI/tree/master/UnitCoverter

Nick Polychronakis solved it in this fork: https://github.com/nickpolychronakis/100DaysOfSwiftUI/tree/master/UnitCoverter

解决方案是将.id(:identifier :)添加到选择器中，使其唯一.

The solution is to add .id(:identifier:) to your picker so it is unique.

可观察的变量:

@State var unit = 0

主选择器:

Picker("Length", selection: $unit) {
                    ForEach(0 ..< inputUnitTypes.count) {
                        Text("\(self.inputUnitTypes[$0].description)")
                    }
                }
                .pickerStyle(SegmentedPickerStyle())

辅助选择器之一，其内容由unit变量确定.

One of secondary pickers which content is determined by the unit variable.

Picker("Length", selection: $inputUnit) {
                        ForEach(0 ..< selected.count) {
                            Text("\(self.selected[$0].description)")
                        }
                    }
                    .id(unit)

这篇关于SwiftUI:更改数据源时Picker无法正确更新的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！