在我的SwiftUI视图中，当Toggle（）更改其状态时，我必须触发一个动作。切换本身仅需要一个Binding。 因此，我试图在@State变量的didSet中触发操作。但是didSet从未被调用。
是否有（其他）触发动作的方式？或以任何方式观察@State变量的值变化？
我的代码如下：
struct PWSDetailView : View {
@ObjectBinding var station: PWS
@State var isDisplayed: Bool = false {
didSet {
if isDisplayed != station.isDisplayed {
PWSStore.shared.toggleIsDisplayed(station)
}
}
}
var body: some View {
VStack {
ZStack(alignment: .leading) {
Rectangle()
.frame(width: UIScreen.main.bounds.width, height: 50)
.foregroundColor(Color.lokalZeroBlue)
Text(station.displayName)
.font(.title)
.foregroundColor(Color.white)
.padding(.leading)
}
MapView(latitude: station.latitude, longitude: station.longitude, span: 0.05)
.frame(height: UIScreen.main.bounds.height / 3)
.padding(.top, -8)
Form {
Toggle(isOn: $isDisplayed)
{ Text("Wetterstation anzeigen") }
}
Spacer()
}.colorScheme(.dark)
}
}
所需的行为是，当Toggle（）更改其状态时触发“ PWSStore.shared.toggleIsDisplayed（station）”操作。
答案 0 :(得分：26)
这是不使用tapGesture的版本。
@State private var isDisplayed = false
Toggle("", isOn: $isDisplayed)
.onReceive([self.isDisplayed].publisher.first()) { (value) in
print("New value is: \(value)")
}
答案 1 :(得分：19)
这是一种更通用的方法，您可以将其应用于Binding中几乎所有内置的View中，例如Pickers，Textfields和Toggle。
extension Binding {
func didSet(execute: @escaping (Value) -> Void) -> Binding {
return Binding(
get: {
return self.wrappedValue
},
set: {
self.wrappedValue = $0
execute($0)
}
)
}
}
用法很简单；
@State var isOn: Bool = false
Toggle("Toggle Title", isOn: $isOn.didSet { (state) in
print(state)
})
答案 2 :(得分：11)
我认为最干净的方法是使用自定义绑定。 这样，您就可以完全控制切换开关何时真正切换
import SwiftUI
struct ToggleDemo: View {
@State private var isToggled = false
var body: some View {
let binding = Binding(
get: { self.isToggled },
set: {
potentialAsyncFunction($0)
}
)
func potentialAsyncFunction(_ newState: Bool) {
//something async
self.isToggled = newState
}
return Toggle("My state", isOn: binding)
}
}
答案 3 :(得分：6)
我找到了一个更简单的解决方案，只需使用onTapGesture：D
List<String> list1 = new ArrayList<>;
list1.add("aa-20");
list1.add("ss-12");
list1.add("ak-2");
list1.add("pp-90");
Collections.sort(list1);
答案 4 :(得分：4)
基于@Legolas Wang的答案。
在切换器中隐藏原始标签时，您只能将tapGesture附加到切换器本身
HStack {
Text("...")
Spacer()
Toggle("", isOn: $stateChange)
.labelsHidden()
.onTapGesture {
// Any actions here.
}
}
答案 5 :(得分：4)
这就是我的编码方式：
Toggle("Title", isOn: $isDisplayed)
.onReceive([self.isDisplayed].publisher.first()) { (value) in
//Action code here
}
更新的代码（Xcode 12，iOS14）：
Toggle("Enabled", isOn: $isDisplayed.didSet { val in
//Action here
})
答案 6 :(得分：4)
如果您使用的是 SwiftUI 2 / iOS 14 ，则可以使用onChange：
struct ContentView: View {
@State private var isDisplayed = false
var body: some View {
Toggle("", isOn: $isDisplayed)
.onChange(of: isDisplayed) { value in
// action...
print(value)
}
}
}
答案 7 :(得分：2)
.init是Binding
的构造函数@State var isDisplayed: Bool
Toggle("some text", isOn: .init(
get: { isDisplayed },
set: {
isDisplayed = $0
print("changed")
}
))
答案 8 :(得分：1)
首先，您实际上是否知道station.isDisplayed的额外KVO通知是一个问题？您是否遇到性能问题？如果没有，那就不用担心。
如果您遇到性能问题，并且已确定它们是由于过多的station.isDisplayed KVO通知引起的，那么接下来要尝试的是消除不必要的KVO通知。您可以通过切换到手动KVO通知来做到这一点。
将此方法添加到station的类定义中：
@objc class var automaticallyNotifiesObserversOfIsDisplayed: Bool { return false }
并使用Swift的willSet和didSet观察者来手动通知KVO观察者，但前提是值更改：
@objc dynamic var isDisplayed = false {
willSet {
if isDisplayed != newValue { willChangeValue(for: \.isDisplayed) }
}
didSet {
if isDisplayed != oldValue { didChangeValue(for: \.isDisplayed) }
}
}
答案 9 :(得分：1)
我认为还可以
struct ToggleModel {
var isWifiOpen: Bool = true {
willSet {
print("wifi status will change")
}
}
}
struct ToggleDemo: View {
@State var model = ToggleModel()
var body: some View {
Toggle(isOn: $model.isWifiOpen) {
HStack {
Image(systemName: "wifi")
Text("wifi")
}
}.accentColor(.pink)
.padding()
}
}
答案 10 :(得分：1)
class PWSStore : ObservableObject {
...
var station: PWS
@Published var isDisplayed = true {
willSet {
PWSStore.shared.toggleIsDisplayed(self.station)
}
}
}
struct PWSDetailView : View {
@ObservedObject var station = PWSStore.shared
...
var body: some View {
...
Toggle(isOn: $isDisplayed) { Text("Wetterstation anzeigen") }
...
}
}
答案 11 :(得分：1)
这是我的方法。我遇到了同样的问题，但是决定将UIKit的UISwitch包装到符合UIViewRepresentable的新类中。
import SwiftUI
final class UIToggle: UIViewRepresentable {
@Binding var isOn: Bool
var changedAction: (Bool) -> Void
init(isOn: Binding<Bool>, changedAction: @escaping (Bool) -> Void) {
self._isOn = isOn
self.changedAction = changedAction
}
func makeUIView(context: Context) -> UISwitch {
let uiSwitch = UISwitch()
return uiSwitch
}
func updateUIView(_ uiView: UISwitch, context: Context) {
uiView.isOn = isOn
uiView.addTarget(self, action: #selector(switchHasChanged(_:)), for: .valueChanged)
}
@objc func switchHasChanged(_ sender: UISwitch) {
self.isOn = sender.isOn
changedAction(sender.isOn)
}
}
然后像这样使用它：
struct PWSDetailView : View {
@State var isDisplayed: Bool = false
@ObservedObject var station: PWS
...
var body: some View {
...
UIToggle(isOn: $isDisplayed) { isOn in
//Do something here with the bool if you want
//or use "_ in" instead, e.g.
if isOn != station.isDisplayed {
PWSStore.shared.toggleIsDisplayed(station)
}
}
...
}
}
答案 12 :(得分：0)
您可以尝试以下操作（这是一种解决方法）：
@State var isChecked: Bool = true
@State var index: Int = 0
Toggle(isOn: self.$isChecked) {
Text("This is a Switch")
if (self.isChecked) {
Text("\(self.toggleAction(state: "Checked", index: index))")
} else {
CustomAlertView()
Text("\(self.toggleAction(state: "Unchecked", index: index))")
}
}
在它下面，创建一个像这样的函数：
func toggleAction(state: String, index: Int) -> String {
print("The switch no. \(index) is \(state)")
return ""
}
答案 13 :(得分：0)
以防万一您不想使用额外的功能，弄乱结构-使用状态并在需要的地方使用它。我知道这不是事件触发器的100％答案，但是状态将以最简单的方式保存和使用。
struct PWSDetailView : View {
@State private var isToggle1 = false
@State private var isToggle2 = false
var body: some View {
ZStack{
List {
Button(action: {
print("\(self.isToggle1)")
print("\(self.isToggle2)")
}){
Text("Settings")
.padding(10)
}
HStack {
Toggle(isOn: $isToggle1){
Text("Music")
}
}
HStack {
Toggle(isOn: $isToggle1){
Text("Music")
}
}
}
}
}
}
答案 14 :(得分：0)
适用于 XCode 12
RuntimeError: JupyterLab failed to build答案 15 :(得分：0)
这是我编写的一个方便的扩展程序，用于在按下切换开关时触发回调。与许多其他解决方案不同，这确实只会在切换开关时触发，而不是在 init 时触发，这对我的用例很重要。这模仿了类似的 SwiftUI 初始值设定项，例如用于 onCommit 的 TextField。
用法：
Toggle("My Toggle", isOn: $isOn, onToggled: { value in
print(value)
})
扩展：
extension Binding {
func didSet(execute: @escaping (Value) -> Void) -> Binding {
Binding(
get: { self.wrappedValue },
set: {
self.wrappedValue = $0
execute($0)
}
)
}
}
extension Toggle where Label == Text {
/// Creates a toggle that generates its label from a localized string key.
///
/// This initializer creates a ``Text`` view on your behalf, and treats the
/// localized key similar to ``Text/init(_:tableName:bundle:comment:)``. See
/// `Text` for more information about localizing strings.
///
/// To initialize a toggle with a string variable, use
/// ``Toggle/init(_:isOn:)-2qurm`` instead.
///
/// - Parameters:
/// - titleKey: The key for the toggle's localized title, that describes
/// the purpose of the toggle.
/// - isOn: A binding to a property that indicates whether the toggle is
/// on or off.
/// - onToggled: A closure that is called whenver the toggle is switched.
/// Will not be called on init.
public init(_ titleKey: LocalizedStringKey, isOn: Binding<Bool>, onToggled: @escaping (Bool) -> Void) {
self.init(titleKey, isOn: isOn.didSet(execute: { value in onToggled(value) }))
}
/// Creates a toggle that generates its label from a string.
///
/// This initializer creates a ``Text`` view on your behalf, and treats the
/// title similar to ``Text/init(_:)-9d1g4``. See `Text` for more
/// information about localizing strings.
///
/// To initialize a toggle with a localized string key, use
/// ``Toggle/init(_:isOn:)-8qx3l`` instead.
///
/// - Parameters:
/// - title: A string that describes the purpose of the toggle.
/// - isOn: A binding to a property that indicates whether the toggle is
/// on or off.
/// - onToggled: A closure that is called whenver the toggle is switched.
/// Will not be called on init.
public init<S>(_ title: S, isOn: Binding<Bool>, onToggled: @escaping (Bool) -> Void) where S: StringProtocol {
self.init(title, isOn: isOn.didSet(execute: { value in onToggled(value) }))
}
}