[我已经研究了这几天，搜寻了Swift和SwiftUI文档，SO，论坛等，似乎找不到答案。
这里是问题；
我有一个SwiftUI自定义视图，该视图对到远程资源的自定义API请求类进行一些状态确定。 View会显示加载状态和失败状态，并通过ViewBuilder传递其主体内容，这样，如果API中的状态成功并且资源数据已加载，它将显示页面内容。
问题是，子类ObservedObject更新时，ViewBuilder内容不会重新呈现。对象会根据UI进行更新（按下按钮等时），但UI不会重新渲染/更新以反映子类ObservedObject内的更改，例如，子类ObservedObject内数组后面的ForEach不会在以下情况下刷新数组内容更改。如果将其移出自定义视图，则ForEach会按预期工作。
我可以确认代码已编译并运行。观察者和debugPrint()的全文显示ApiObject正在正确更新状态，并且视图反映了ApiState的更改绝对正确。它只是ViewBuilder的Content。我认为这是因为ViewBuilder只会被调用一次。
EDIT：上面的段落应该是提示，ApiState正确更新，但是在将大量日志记录到应用程序中之后，UI并未监听子类ObservedObject的发布。属性在变化，状态也在变化，但是UI对此没有反应。同样，下一个句子被证明是错误的，我在VStack中再次进行了测试，并且该组件仍然没有重新渲染，这意味着我在错误的位置查看！
如果是这种情况，VStack和其他此类元素如何解决？还是因为我的ApiObjectView在状态更改时被重新渲染而导致子视图“重置”？尽管在这种情况下，我希望它可以接管新数据并按预期工作，但它永远不会重新呈现。
有问题的代码在下面的CustomDataList.swift和ApiObjectView.swift中。我留下的评论指向正确的方向。
这里是示例代码；
// ApiState.swift
// Stores the API state for where the request and data parse is currently at.
// This drives the ApiObjectView state UI.
import Foundation
enum ApiState: String
{
case isIdle
case isFetchingData
case hasFailedToFetchData
case isLoadingData
case hasFailedToLoadData
case hasUsableData
}
// ApiObject.swift
// A base class that the Controllers for the app extend from.
// These classes can make data requests to the remote resource API over the
// network to feed their internal data stores.
class ApiObject: ObservableObject
{
@Published var apiState: ApiState = .isIdle
let networkRequest: NetworkRequest = NetworkRequest(baseUrl: "https://api.example.com/api")
public func apiGetJson<T: Codable>(to: String, decodeAs: T.Type, onDecode: @escaping (_ unwrappedJson: T) -> Void) -> Void
{
self.apiState = .isFetchingData
self.networkRequest.send(
to: to,
onComplete: {
self.apiState = .isLoadingData
let json = self.networkRequest.decodeJsonFromResponse(decodeAs: decodeAs)
guard let unwrappedJson = json else {
self.apiState = .hasFailedToLoadData
return
}
onDecode(unwrappedJson)
self.apiState = .hasUsableData
},
onFail: {
self.apiState = .hasFailedToFetchData
}
)
}
}
// DataController.swift
// This is a genericised example of the production code.
// These controllers build, manage and serve their resource data.
// Subclassed from the ApiObject, inheriting ObservableObject
import Foundation
import Combine
class CustomDataController: ApiObject
{
@Published public var customData: [CustomDataStruct] = []
public func fetch() -> Void
{
self.apiGetJson(
to: "custom-data-endpoint ",
decodeAs: [CustomDataStruct].self,
onDecode: { unwrappedJson in
self.customData = unwrappedJson
}
)
}
}
这是在ForEach更改为绑定数组属性时重新呈现其ObservedObject的视图。
// CustomDataList.swift
// This is the SwiftUI View that drives the content to the user as a list
// that displays the CustomDataController.customData.
// The ForEach in this View
import SwiftUI
struct CustomDataList: View
{
@ObservedObject var customDataController: CustomDataController = CustomDataController()
var body: some View
{
ApiObjectView(
apiObject: self.customDataController,
onQuit: {}
) {
List
{
Section(header: Text("Custom Data").padding(.top, 40))
{
ForEach(self.customDataController.customData, id: \.self, content: { customData in
// This is the example that doesn't re-render when the
// customDataController updates its data. I have
// verified via printing at watching properties
// that the object is updating and pushing the
// change.
// The ObservableObject updates the array, but this ForEach
// is not run again when the data is changed.
// In the production code, there are buttons in here that
// change the array data held within customDataController.customData.
// When tapped, they update the array and the ForEach, when placed
// in the body directly does reflect the change when
// customDataController.customData updates.
// However, when inside the ApiObjectView, as by this example,
// it does not.
Text(customData.textProperty)
})
}
}
.listStyle(GroupedListStyle())
}
.navigationBarTitle(Text("Learn"))
.onAppear() {
self.customDataController.fetch()
}
}
}
struct CustomDataList_Previews: PreviewProvider
{
static var previews: some View
{
CustomDataList()
}
}
这是有问题的自定义视图，不会重新呈现其内容。
// ApiObjectView
// This is the containing View that is designed to assist in the UI rendering of ApiObjects
// by handling the state automatically and only showing the ViewBuilder contents when
// the state is such that the data is loaded and ready, in a non errornous, ready state.
// The ViewBuilder contents loads fine when the view is rendered or the state changes,
// but the Content is never re-rendered if it changes.
// The state renders fine and is reactive to the object, the apiObjectContent
// however, is not.
import SwiftUI
struct ApiObjectView<Content: View>: View {
@ObservedObject var apiObject: ApiObject
let onQuit: () -> Void
let apiObjectContent: () -> Content
@inlinable public init(apiObject: ApiObject, onQuit: @escaping () -> Void, @ViewBuilder content: @escaping () -> Content) {
self.apiObject = apiObject
self.onQuit = onQuit
self.apiObjectContent = content
}
func determineViewBody() -> AnyView
{
switch (self.apiObject.apiState) {
case .isIdle:
return AnyView(
ActivityIndicator(
isAnimating: .constant(true),
style: .large
)
)
case .isFetchingData:
return AnyView(
ActivityIndicator(
isAnimating: .constant(true),
style: .large
)
)
case .isLoadingData:
return AnyView(
ActivityIndicator(
isAnimating: .constant(true),
style: .large
)
)
case .hasFailedToFetchData:
return AnyView(
VStack
{
Text("Failed to load data!")
.padding(.bottom)
QuitButton(action: self.onQuit)
}
)
case .hasFailedToLoadData:
return AnyView(
VStack
{
Text("Failed to load data!")
.padding(.bottom)
QuitButton(action: self.onQuit)
}
)
case .hasUsableData:
return AnyView(
VStack
{
self.apiObjectContent()
}
)
}
}
var body: some View
{
self.determineViewBody()
}
}
struct ApiObjectView_Previews: PreviewProvider {
static var previews: some View {
ApiObjectView(
apiObject: ApiObject(),
onQuit: {
print("I quit.")
}
) {
EmptyView()
}
}
}
现在，如果不使用ApiObjectView并将其内容直接放置在视图中，则以上所有代码都可以正常工作。
但是，这对于代码重用和体系结构来说太可怕了，这样虽然好看又整洁，但是不起作用。
是否还有其他方法可以解决此问题，例如通过ViewModifier或View扩展名？
对此的任何帮助将不胜感激。
正如我所说，我似乎找不到任何人遇到此问题，也找不到任何在线资源可以为我指出正确的方向来解决此问题，或者可能是由什么引起的，例如ViewBuilder文档中概述的。] >
编辑：要添加一些有趣的东西，我此后向CustomDataList添加了一个倒数计时器，该计时器每1秒更新一次标签。 IF
我已经研究了这几天，搜寻了Swift和SwiftUI文档，SO，论坛等，似乎找不到答案。这是问题所在；我有一个SwiftUI自定义视图，它可以执行...
[拔出我的头发一周后就发现了，这是一个未记录的问题，因为将ObservableObject分为子类，如此SO answer所示。