这是我在SwiftUI代码中遇到的问题的重现。假设有一个设备列表，并且每个设备都有一些连接信息（是否启用）。
在SwiftUI中使用经典列表，每台设备都会显示一个DeviceView。 为了方便起见，我想在顶部添加几个箭头以在设备之间切换，而不必每次都返回列表（了解一下，例如iOS中的Mail应用程序）。 因此，我没有从列表中调用DeviceView，而是在调用MotherDeviceView之前存储了当前设备的信息。当我点击顶部的箭头时，MotherDeviceView再次调用DeviceView并更新视图。
struct Device: Identifiable {
var id = Int()
var deviceName = String()
var isWifiOn = Bool()
var isCellularOn = Bool()
var isBluetoothOn = Bool()
}
let devices: [Device] = [
Device(id: 0, deviceName: "iPhone", isWifiOn: true, isCellularOn: false, isBluetoothOn: true),
Device(id: 1, deviceName: "iPod", isWifiOn: false, isCellularOn: false, isBluetoothOn: true),
Device(id: 2, deviceName: "iPad", isWifiOn: false, isCellularOn: true, isBluetoothOn: false)
]
// main view, with list of devices
struct DeviceTab: View {
var body: some View {
NavigationView {
List(devices) { device in
NavigationLink(destination: MotherDeviceView(device: device)){
Text(device.deviceName)
}
}.navigationBarTitle(Text("Devices"))
}
}
}
// the list call this view and pass the device to DeviceView.
// Using this view is possible to go to the other device using the arrows on the top
// without returning to the list
struct MotherDeviceView: View {
@State var device: Device
var body: some View {
VStack{
DeviceView(device: $device)
}
.navigationBarItems(trailing: arrows)
}
private var arrows: some View {
HStack{
Button(action: { self.previous() },
label: { Image(systemName: "chevron.up") } )
.padding(.horizontal, 10)
Button(action: { self.next() },
label: { Image(systemName: "chevron.down") } )
}
}
func previous() {
if device.id == 0 { return }
device = devices[device.id - 1]
}
func next() {
if device.id == 2 { return }
device = devices[device.id + 1]
}
}
// DeviceView
struct DeviceView: View {
@Binding var device: Device
var body: some View {
VStack{
Spacer()
Text("This is the device number: " + String(device.id))
Spacer()
ToggleSection(dev: $device)
Spacer()
}.navigationBarTitle(device.deviceName)
}
}
// Toggle part of DeviceView
struct ToggleSection: View {
@Binding var dev: Device
@State var toggleOn: [Bool] = [false, false, false]
var body: some View {
VStack{
Text(dev.deviceName)
.fontWeight(.bold)
Toggle(isOn: $toggleOn[0], label: { Text("Wifi") } )
.padding()
Toggle(isOn: $toggleOn[1], label: { Text("Cellular") } )
.padding()
Toggle(isOn: $toggleOn[2], label: { Text("Bluetooth") } )
.padding()
}
.onAppear{ self.initialConfigToggle() }
// with onAppear is okay, but when I use the top arrows, this section does not update
}
private func initialConfigToggle() {
self.toggleOn[0] = self.dev.isWifiOn
self.toggleOn[1] = self.dev.isCellularOn
self.toggleOn[2] = self.dev.isBluetoothOn
}
}
但是DeviceView中有一个部分ToggleSection不会更新，我也不知道如何解决。 也许要强制更新？但是我认为这不是正确的答案（但是我什至不知道如何强制更新）。
我认为，如果在ToggleSection中有@Binding而不是@State，也许是正确的答案，但这是行不通的。 此示例将起作用（除了未更新的切换开关之外）
谢谢！
答案 0 :(得分：1)
这是一种可能的方法，它添加了用于设备存储的显式视图模型，并以在存储中精确进行修改的方式（为了应对设备值）加入所有视图。
通过Xcode 11.4 / iOS 13.4测试
修改后的代码：
import SwiftUI
import Combine
struct Device: Identifiable {
var id = Int()
var deviceName = String()
var isWifiOn = Bool()
var isCellularOn = Bool()
var isBluetoothOn = Bool()
}
class DeviceStorage: ObservableObject {
@Published var devices: [Device] = [
Device(id: 0, deviceName: "iPhone", isWifiOn: true, isCellularOn: false, isBluetoothOn: true),
Device(id: 1, deviceName: "iPod", isWifiOn: false, isCellularOn: false, isBluetoothOn: true),
Device(id: 2, deviceName: "iPad", isWifiOn: false, isCellularOn: true, isBluetoothOn: false)
]
}
// main view, with list of devices
struct DeviceTab: View {
@ObservedObject var vm = DeviceStorage() // for demo, can be injected via init
var body: some View {
NavigationView {
List(Array(vm.devices.enumerated()), id: \.element.id) { i, device in
NavigationLink(destination: MotherDeviceView(vm: self.vm, selectedDevice: i)) {
Text(device.deviceName)
}
}.navigationBarTitle(Text("Devices"))
}
}
}
struct MotherDeviceView: View {
@ObservedObject var vm: DeviceStorage // reference type, so have same
@State private var selected: Int // selection index
init(vm: DeviceStorage, selectedDevice: Int) {
self.vm = vm
self._selected = State<Int>(initialValue: selectedDevice)
}
var body: some View {
VStack{
DeviceView(device: $vm.devices[selected]) // bind to selected
}
.navigationBarItems(trailing: arrows)
}
private var arrows: some View {
HStack{
Button(action: { self.previous() },
label: { Image(systemName: "chevron.up") } )
.padding(.horizontal, 10)
Button(action: { self.next() },
label: { Image(systemName: "chevron.down") } )
}
}
func previous() {
if vm.devices[selected].id == 0 { return }
selected -= 1 // change selection
}
func next() {
if vm.devices[selected].id == 2 { return }
selected += 1 // change selection
}
}
// DeviceView
struct DeviceView: View {
@Binding var device: Device
var body: some View {
VStack{
Spacer()
Text("This is the device number: " + String(device.id))
Spacer()
ToggleSection(dev: $device)
Spacer()
}.navigationBarTitle(device.deviceName)
}
}
// Toggle part of DeviceView
struct ToggleSection: View {
@Binding var dev: Device
var body: some View {
VStack{
Text(dev.deviceName)
.fontWeight(.bold)
// all below bound directly to model !!!
Toggle(isOn: $dev.isWifiOn, label: { Text("Wifi") } )
.padding()
Toggle(isOn: $dev.isCellularOn, label: { Text("Cellular") } )
.padding()
Toggle(isOn: $dev.isBluetoothOn, label: { Text("Bluetooth") } )
.padding()
}
}
}