问题描述
我遇到了一个奇怪的行为,@State 属性在另一个视图中更改后没有在其原始视图中正确更新。我使用的是 Xcode 12.3 和 iOS 14。
发生的情况是@State“会话”基于值的项目和@State“流”基于值的项目作为绑定参数发送到另一个视图。当一个按钮在那里被点击时,它会改变它们的值,并且原始视图中的 fullScreenCover 调用应该从 switch 语句获得正确的视图以显示在流程中的下一个。但是,除非我包含一个 onChange 修饰符来查找两个 @State 属性中的任何一个中的更改,否则该 switch 语句中的“会话”项为零。 onChange 调用中无需包含任何代码即可实现此效果。
我对 SwiftUI 还是比较陌生(尽管在 iOS 和 Mac 开发方面经验丰富)。但这让我很困惑。我不明白为什么它没有按预期工作,也不明白为什么添加一个空的 onChange 处理程序使它工作。
SortedSet
解决方法
class ObservationSession: //Codable,//implement Codable manually
ObservableObject {
public let id: UUID
//This allows you to observe the individual variable
@Published public var name: String
public init(name: String) {
self.name = name
self.id = UUID()
}
}
struct SessionListModals {
enum Flow: Identifiable {
case configuration
case observation
case newSession
var id: Flow { self }
}
}
// ContentView
class ContentViewModel: ObservableObject {
@Published var mutableSession: ObservationSession?
}
struct ContentView: View {
//State stores the entire object and observes it as a whole it does not individually observe its variables that is why .onChange works
@StateObject var vm: ContentView3Model = ContentView3Model()
@State private var flow: SessionListModals.Flow?
var body: some View {
VStack {
Button("New Session",action: {
//Since you want to change it programatically you have to put them in another object
vm.mutableSession = ObservationSession(name: "")
flow = .newSession
})
.padding()
}
.fullScreenCover(item: $flow) {
viewForFlow($0)
}
}
@ViewBuilder private func viewForFlow(_ flow: SessionListModals.Flow) -> some View {
switch flow {
case .newSession:
// MARK: - Show New Session View
NavigationView {
NewSessionView(session: $vm.mutableSession,flow: $flow)
.navigationTitle("Create a session")
.navigationBarItems(leading: Button("Cancel",action: {
self.flow = nil
}))
}
case .observation:
// MARK: - Show RecordingView
NavigationView {
let name = vm.mutableSession?.name ?? "Unnamed session"
RecordingView(sessionName: name)
.navigationBarItems(leading: Button("Close",action: {
self.flow = nil
}))
}
default:
NavigationView {
EmptyView()
.navigationBarItems(leading: Button("Close",action: {
self.flow = nil
}))
}
}
}
}