我在 SwiftUI 中使用泛型，在尝试利用 ViewBuilder 闭包将数据传递到泛型视图时遇到了数据持久性问题。我的目标是拥有一个管理从 API 接收数据并将其传递给通用视图的 shell 视图，如 ViewBuilder 块中定义的那样。所有数据似乎都成功地传递给了 inits，包括我的 generic BasicListView，但是当body被调用时，没有任何列表数据被持久化。
我认为通过代码来解释这个问题会更容易。为这里的长代码转储道歉：
import SwiftUI
import Combine
// This is the blank "shell" View that manages passing the data into the viewBuilder through the @ViewBuilder block
struct BlankView<ListItem, Content:View>: View where ListItem: Listable {
let api = GlobalAPI.shared
@State var list: [ListItem] = []
@State var viewBuilder: ([ListItem]) -> Content // Passing in generic [ListItem] here
init(@ViewBuilder builder: @escaping ([ListItem]) -> Content) {
self._viewBuilder = State<([ListItem]) -> Content>(initialValue: builder)
}
var body: some View {
viewBuilder(list) // List contained in Blank View passed into viewBuilder Block here
.multilineTextAlignment(.center)
.onReceive(GlobalAPI.shared.listDidChange) { item in
if let newItem = item as? ListItem {
self.list.append(newItem) // Handle API updates here
}
}
}
}
// And Here is the implementation of the Blank View
struct TestView: View {
public var body: some View {
BlankView<MockListItem, VStack>() { items in // A list of items will get passed into the block
VStack {
Text("Add a row") // Button to add row via API singleton
.onTapGesture {
GlobalAPI.shared.addListItem()
}
BasicListView(items: items) { // List view init'd with items
Text("Hold on to your butts") // Destination
}
}
}
}
}
// Supporting code
// The generic list view/cell
struct BasicListView<Content: View, ListItem:Listable>: View {
@State var items: [ListItem]
var destination: () -> Content
init(items: [ListItem], @ViewBuilder builder: @escaping () -> Content) {
self._items = State<[ListItem]>(initialValue: items) // Items successfully init'd here
self.destination = builder
}
var body: some View {
List(items) { item in // Items that were passed into init no longer present here, this runs on a blank [ListItem] array
BasicListCell(item: item, destination: self.destination)
}
}
}
struct BasicListCell<Content: View, ListItem:Listable>: View {
@State var item: ListItem
var destination: () -> Content
var body: some View {
NavigationLink(destination: destination()) {
HStack {
item.photo
.resizable()
.frame(width: 50.0, height: 50.0)
.font(.largeTitle)
.cornerRadius(25.0)
VStack (alignment: .leading) {
Text(item.title)
.font(.headline)
Text(item.description)
.font(.subheadline)
.foregroundColor(.secondary)
}
}
}
}
}
// The protocol and mock data struct
protocol Listable: Identifiable {
var id: UUID { get set }
var title: String { get set }
var description: String { get set }
var photo: Image { get set }
}
public struct MockListItem: Listable {
public var photo: Image = Image(systemName:"photo")
public var id = UUID()
public var title: String = "Title"
public var description: String = "This is the description"
static let all = [MockListItem(), MockListItem(), MockListItem(), MockListItem()]
}
// A global API singleton for testing data updates
class GlobalAPI {
static let shared = GlobalAPI()
var listDidChange = PassthroughSubject<MockListItem, Never>()
var newListItem:MockListItem? = nil {
didSet {
if let item = newListItem {
listDidChange.send(item)
}
}
}
func addListItem() {
newListItem = MockListItem()
}
}
这是 ViewBuilder 块的正确实现，还是不鼓励尝试通过 View builder 块传递数据？
注意：什么工作
如果我直接传入静态 Mock 数据，视图将正确绘制自己，如下所示：
struct TestView: View {
public var body: some View {
BlankView<MockListItem, VStack>() { items in // A list of items will get passed into the block
VStack {
Text("Add a row") // Button to add row via API singleton
.onTapGesture {
GlobalAPI.shared.addListItem()
}
BasicListView(items: MockListItem.all) { // List view init'd with items
Text("Hold on to your butts") // Destination
}
}
}
}
}
有任何想法吗？感谢大家的帮助和反馈。
