SwiftUI ForEEach协议的结果是 " 要求内容符合无障碍路标 "
原标题：SwiftUI ForEach of protocols results in "requirement that Content conform to AccessibilityRotorContent "
I m looking at iterating over an array of protocols and get them each to render a view. The protocol has a buildView function that returns any View, but calling this inside my view has the error:
Static method buildExpression requires that Content conform to AccessibilityRotorContent
Here s the code below, I don t really know what s going on and would greatly appreciate some help in debugging it.
import UIKit
import SwiftUI
import PlaygroundSupport
protocol ViewItem: AnyObject, Hashable, Identifiable {
var id: UUID { get }
func buildView() -> any View
}
class ViewOne: ViewItem {
let id: UUID = UUID()
func buildView() -> any View {
Text("View one")
}
static func == (lhs: ViewOne, rhs: ViewOne) -> Bool {
lhs.id == rhs.id
}
func hash(into hasher: inout Hasher) {
hasher.combine(id)
}
}
class ViewTwo: ViewItem {
let id: UUID = UUID()
func buildView() -> any View {
Text("View two")
}
static func == (lhs: ViewTwo, rhs: ViewTwo) -> Bool {
lhs.id == rhs.id
}
func hash(into hasher: inout Hasher) {
hasher.combine(id)
}
}
struct ContentView: View {
let viewItems: [any ViewItem]
var body: some View {
VStack {
ForEach(viewItems, id: .id) { viewItem in
viewItem.buildView() <------------------ ERROR HERE
}
}
}
}
问题回答
func buildView() -> any View
The code above is not allowed within body, with or without ForEach.
var body: some View {
VStack {
createAnyView() // ❌
createSomeView() // ✅
}
}
func createAnyView() -> any View {
Text("any view")
}
func createSomeView() -> some View {
Text("some view")
}
AFAIK, the body must contain some View or a type-erased AnyView. So, an approach is changing your protocol function to:
protocol ViewItem {
...
func buildView() -> AnyView
}
class ViewOne: ViewItem {
func buildView() -> AnyView {
AnyView(
Text("View one")
)
}
}
However, it has drawbacks such as unpredictable view state, animation, performance, etc... since SwiftUI doesn t even know what View it will be to optimize when it needs to re-render. You can check this out Demystify SwiftUI performance.
Thus, if I were you, I would go with some View solution:
protocol ViewItem {
...
associatedtype ContentView: View
func buildView() -> ContentView
}
Then I will wrap each type into a kind of builder, because passing directly ViewItem into a View will force the input param to any as mentioned in SE-0335.
enum Content: View, Identifiable {
case viewOne(ViewOne)
case viewTwo(ViewTwo)
var body: some View {
switch self {
case .viewOne(let viewOne):
viewOne.buildView()
case .viewTwo(let viewTwo):
viewTwo.buildView()
}
}
var id: ObjectIdentifier {
switch self {
case .viewOne(let viewOne):
return viewOne.id
case .viewTwo(let viewTwo):
return viewTwo.id
}
}
}
Finally, implement ContentView as normal:
struct ContentView: View {
var items: [Content]
var body: some View {
VStack {
ForEach(items) { item in
item.body
}
}
}
}
#Preview {
ContentView(items: [
.viewOne(.init()),
.viewTwo(.init())
])
}
Side note: If you have several return statements in each ViewItem, you might consider adding @ViewBuilder to your protocol to use the power of function builder.
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