swiftui - 与@ObjectBinding 和@EnvironmentObject 绑定
问题描述
2019 年 7 月 28 日。我仍然对下面的代码有疑问。我想将数据模型从 ContentView 中分离出来。所以我制作了一个单独的文件并添加了类,如下所示:
import SwiftUI
import Combine
class User: BindableObject {
let willChange = PassthroughSubject<Void, Never>()
var username : String = "Jan" { willSet { willChange.send() }}
var password : String = "123456" { willSet { willChange.send() } }
var emailAddress : String = "jan@mail.nl" { willSet { willChange.send() } }
}
#if DEBUG
struct User_Previews: PreviewProvider {
static var previews: some View {
User()
.environmentObject(User())
}
}
#endif
但是这不起作用,我收到一个错误:
Protocol type 'Any' cannot conform to 'View' because only concrete types can conform to protocols
# if DEBUG 中的 .environmentObject(User()) 行发生错误。
在观看了一些视频后,我编写了以下代码(包括 Xcode 11 beta 4 的更改)。来自 dfd 和 MScottWaller 的两个答案的提示已包含在代码中。
import Combine
import SwiftUI
class User: BindableObject {
let willChange = PassthroughSubject<Void, Never>()
var username = "Jan" { willSet { willChange.send() } }
var password = "123456" { willSet { willChange.send() } }
var emailAddress = "jan@mail.nl" { willSet { willChange.send() } }
}
struct ContentView: View {
@EnvironmentObject var user: User
private func buttonPressed() {
print(user.username) // in Simulator
}
var body: some View {
VStack {
TextField("Username", text: $user.username)
TextField("Password", text: $user.password)
TextField("Emailaddress", text: $user.emailAddress)
Button(action: buttonPressed) {
Text("Press me!")
}
}
}
}
#if DEBUG
struct ContentView_Previews: PreviewProvider {
static var previews: some View {
ContentView()
.environmentObject(User())
}
}
#endif
但现在进入下一部分。如果我有另一种看法……那我该如何参考数据呢?由于事实的来源在上面的 ViewContent() 视图中。答案是:
import SwiftUI
struct DetailView: View {
@EnvironmentObject var user: User
var body: some View {
VStack {
TextField("Username", text: $user.username)
TextField("Password", text: $user.password)
TextField("Email", text: $user.emailAddress)
}
}
}
#if DEBUG
struct DetailView_Previews: PreviewProvider {
static var previews: some View {
DetailView()
.environmentObject(User())
}
}
#endif
不要忘记编辑 SceneDelegate(来自 dfd 的答案):
var user = User()
func scene(_ scene: UIScene, willConnectTo session: UISceneSession, options connectionOptions: UIScene.ConnectionOptions) {
if let windowScene = scene as? UIWindowScene {
let window = UIWindow(windowScene: windowScene)
window.rootViewController = UIHostingController(rootView: ContentView()
.environmentObject(user)
)
self.window = window
window.makeKeyAndVisible()
}
}
解决方案
在您的 DetailView 预览中,不要为 get 附加 environmentObject。看看我是如何在下面的 PreviewProvider 中添加它的。当您运行实际的应用程序时,您需要对 SceneDelegate 中的 ContentView 执行相同的操作
import SwiftUI
struct DetailView: View {
@EnvironmentObject var user: User
var body: some View {
HStack {
TextField("Username", text: $user.username)
Text("Hello world!")
}
}
}
#if DEBUG
struct DetailView_Previews: PreviewProvider {
static var previews: some View {
DetailView()
.environmentObject(User())
}
}
#endif
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