[英]How to reference with SwiftUI EnvironmentObject
根据 Apple 官方指南,我猜如果每个视图只有一个 environmentObject,那么这样做就可以了。 当碰巧不止一个时,我不确定如何引用 object。
struct LandmarkList: View {
@EnvironmentObject private var userData: UserData
...
ForEach(userData.landmarks) { landmark in
if !self.userData.showFavoritesOnly || landmark.isFavorite {
NavigationLink(
destination: LandmarkDetail(landmark: landmark)
.environmentObject(self.userData)
) {
LandmarkRow(landmark: landmark)
}
}
}
以上是苹果官方指南中的代码,位于 LandMarkDetail 文件中
struct LandmarkDetail: View {
@EnvironmentObject var userData: UserData
我想知道 LandMarkList 中的 environmentObject 是如何引用 LandmarkDetail 中的环境 object 的。 他们有约束力吗? 我在文件中添加了第二个 EnvironmentObject 但什么也没发生
struct LandmarkDetail: View {
@EnvironmentObject var userData: UserData
@EnvironmentObject var testData: UserData
那么如何引用userData和testData中的每一个
编辑:我尝试在以下文件中添加环境 object:
import SwiftUI
struct LandmarkList: View {
@EnvironmentObject private var userData: UserData
@EnvironmentObject private var testData: TestData
var body: some View {
NavigationView {
List {
Toggle(isOn: $userData.showFavoritesOnly) {
Text("Show Favorites Only")
}
Toggle(isOn: $testData.testbool) {
Text("Test")
}
...
struct LandmarksList_Previews: PreviewProvider {
static var previews: some View {
ForEach(["iPhone SE", "iPhone XS Max"], id: \.self) { deviceName in
LandmarkList()
.previewDevice(PreviewDevice(rawValue: deviceName))
.previewDisplayName(deviceName)
}
.environmentObject(UserData())
.environmentObject(TestData())
}
}
final class TestData: ObservableObject {
@Published var testbool = false
}
预览崩溃了。 Xcode 可以编译但立即给出以下错误
Fatal error: No ObservableObject of type TestData found.
A View.environmentObject(_:) for TestData may be missing as an ancestor of this view.: file /BuildRoot/Library/Caches/com.apple.xbs/Sources/Monoceros_Sim/Monoceros-30.4/Core/EnvironmentObject.swift, line 55
2019-10-12 19:07:46.565707+0800 Landmarks[13034:643289] Fatal error: No ObservableObject of type TestData found.
A View.environmentObject(_:) for TestData may be missing as an ancestor of this view.: file /BuildRoot/Library/Caches/com.apple.xbs/Sources/Monoceros_Sim/Monoceros-30.4/Core/EnvironmentObject.swift, line 55
不要忘记在 Scenedelegate 中执行此操作以绑定您的 object:
window.rootViewController = UIHostingController(rootView: contentView.environmentObject(TestData()).environmentObject(UserData()))
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