SwiftUI - onChange不被呼叫
SwiftUI - onChange不被呼叫
提问于 2022-08-07 03:28:05
首先添加代码，以帮助更好地理解问题。
struct MainSetupView: View {
@StateObject var viewModel: MainViewModel
var body: some View {
VStack {
switch viewModel.state {
case .idle:
Color.clear.onAppear(perform: { viewModel.prepare() })
case .loading:
ProgressView()
case .showMessage(let messageType, let messageText):
ErrorHandlingView(messageType: messageType, messageText: messageText)
}
}.onAppear() {
viewModel.state = .idle
}
}
}
struct ErrorHandlingView: View {
@State var messageType: String
var messageText: String
@State private var messageViewImageDetails: (imageName: String, isSystemImage: Bool) = (imageName: "", isSystemImage: false)
var body: some View {
VStack {
MessageViewWithActions(imageName: messageViewImageDetails.imageName, isSystemImage: messageViewImageDetails.isSystemImage, mainMessageText: messageText)
}.onChange(of: messageType) {_ in
self.messageViewImageDetails = getImageForError()
// call more functions
}
}
private func getImageForError() -> (imageName: String, isSystemImage: Bool) {
var imageName = ""
var isSystemImage = false
switch messageType {
case "noInternetError":
imageName = "xmark.icloud"
isSystemImage = true
case "userSignedOut":
imageName = "person.crop.circle.fill.badge.xmark"
isSystemImage = true
case "userSignedIn":
imageName = "person.crop.circle.badge.checkmark"
isSystemImage = true
// more cases.
default:
imageName = "info.circle"
isSystemImage = true
}
return (imageName: imageName, isSystemImage: isSystemImage)
}
}如果"MainSetupView“是打开的，并且我收到了一条消息，即.showMessage，则显示" ErrorHandlingView”，并在调用ErrorHandlingView时设置"messageType“和"messageText”。在显示第一条消息时，假设我收到了另一条消息，然后再次调用"ErrorHandlingView“，现在使用的是不同的消息类型。但是，"onChange(of: messageType)“中的"ErrorHandlingView”从未被调用。
"onChange( of : messageType)“调用一个函数"getImageForError”，该函数根据messageType的值告诉应用程序要显示哪个图像。由于onChange中的代码没有被执行，"getImageForError“永远不会被调用，因此"messageViewImageDetails”永远不会被填充，从而导致视图中没有图像。
知道为什么没有执行.onChange()吗？我做错了什么？
注意:我有很多代码，我正在分享一些代码，我认为这些代码会有所帮助。如果需要更多代码，请告诉我。
编辑：为MessageViewWithActions添加代码。
struct MessageViewWithActions: View {
// Image properties
var imageName: String?
var isSystemImage: Bool = false
// Text properties
var mainMessageText: String?
var body: some View {
ScrollView {
VStack {
Text("")
VStack {
if let imageName = imageName {
if isSystemImage {
Image(systemName: imageName)
} else {
Image(imageName)
}
}
}.frame(maxWidth: .infinity).padding(.bottom, 8)
if let mainMessageText = mainMessageText {
Text(mainMessageText).font(.subheadline).fixedSize(horizontal: false, vertical: true)
}
}
}
}
}回答 1
Stack Overflow用户
发布于 2022-08-07 04:06:32
将messageType更改为绑定变量而不是状态变量有效。分享今后更新的代码：
struct MainSetupView: View {
@StateObject var viewModel: MainViewModel
@State var messageType: String
var body: some View {
VStack {
switch viewModel.state {
case .idle:
Color.clear.onAppear(perform: { viewModel.prepare() })
case .loading:
ProgressView()
case .showMessage(_, let messageText):
ErrorHandlingView(messageType: messageType, messageText: messageText)
}
}.onAppear() {
viewModel.state = .idle
}.onReceive(viewModel.$state, perform: { (value) in
switch value {
case .showMessage(let messageType, _):
self.messageType = messageType
case .idle, .loading:
print("")
}
})
}
}
struct ErrorHandlingView: View {
@Binding var messageType: String
var messageText: String
@State private var messageViewImageDetails: (imageName: String, isSystemImage: Bool) = (imageName: "", isSystemImage: false)
var body: some View {
VStack {
MessageViewWithActions(imageName: messageViewImageDetails.imageName, isSystemImage: messageViewImageDetails.isSystemImage, mainMessageText: messageText)
}.onChange(of: messageType) {_ in
self.messageViewImageDetails = getImageForError()
// call more functions
}
}
private func getImageForError() -> (imageName: String, isSystemImage: Bool) {
var imageName = ""
var isSystemImage = false
switch messageType {
case "noInternetError":
imageName = "xmark.icloud"
isSystemImage = true
case "userSignedOut":
imageName = "person.crop.circle.fill.badge.xmark"
isSystemImage = true
case "userSignedIn":
imageName = "person.crop.circle.badge.checkmark"
isSystemImage = true
// more cases.
default:
imageName = "info.circle"
isSystemImage = true
}
return (imageName: imageName, isSystemImage: isSystemImage)
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/73264683
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