[英]SwiftUI - onChange not getting called
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”打开并且我收到一条消息,即.showMessage,则会显示“ErrorHandlingView”,并且在调用ErrorHandlingView 时设置“messageType”和“messageText”。 在显示第一条消息时,假设我收到另一条消息并且“ErrorHandlingView”再次被调用,现在使用不同的消息类型。 然而,“ErrorHandlingView”中的“onChange(of: messageType)”永远不会被调用。
“onChange(of: messageType)”调用 function “getImageForError”,它告诉应用程序根据 messageType 的值显示哪个图像。 由于 onChange 中的代码没有被执行,因此永远不会调用“getImageForError”,因此永远不会填充“messageViewImageDetails”,这会导致视图没有图像。
知道为什么 is.onChange() 没有被执行吗? 我究竟做错了什么?
注意:我有很多代码,我正在分享一些我认为会有所帮助的代码。 让我知道是否需要更多代码。
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)
}
}
}
}
}
将 messageType 更改为 Binding var 而不是 State var 有效。 共享未来的更新代码:
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)
}
}
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