调用中缺少参数'View Call'参数

Question

我很难理解为什么在调用这个视图时必须给予名为vm的Popup视图依赖项，因为它是可观察的

struct ContentView: View {
@State private var showPopup1 = false
var body: some View {
VStack {
Button(action: { withAnimation {  self.showPopup1.toggle()}}){
Text("showPopup1")  }
Text("title")
DetailView()  /// this line shows error
}

}
}
struct DetailView:View {
@ObservedObject  var vm:ViewModel
var body : some View {
Text("value from VM")

}
}
class ViewModel: ObservableObject {
@Published var title:String = ""

}

Answer 1

在初始化视图时，必须设置vm属性。这是通常的方式。

struct ContentView: View {
@State private var showPopup1 = false
var body: some View {
VStack {
Button(action: { withAnimation {  self.showPopup1.toggle()}}){
Text("showPopup1")  }
Text("title")
DetailView(vm: ViewModel()) // Initiate your ViewModel() and pass it as DetailView() parameter
}
}
}
struct DetailView:View {
var vm: ViewModel
var body : some View {
Text("value from VM")
}
}
class ViewModel: ObservableObject {
@Published var title:String = ""
}

或者你可以使用@EnvironmentObject。您必须将.environmentObject(yourObject(传递到要使用Object的视图，但在传递它之前，您必须对其进行初始化。

顺便说一句，我不确定这是否是一个好方法，因为environmentObject可以访问您在其上声明.environmentObject的视图的所有子视图，并且您通常只需要一个ViewModel来访问一个视图。

struct ContentView: View {
@State private var showPopup1 = false
var body: some View {
VStack {
Button(action: { withAnimation {  self.showPopup1.toggle()}}){
Text("showPopup1")  }
Text("title")
DetailView().environmentObject(ViewModel()) // Pass your ViewModel() as an environmentObject
}
}
}
struct DetailView:View {
@EnvironmentObject var vm: ViewModel // you can now use your vm, and access it the same say in all childs view of DetailView
var body : some View {
Text("value from VM")
}
}
class ViewModel: ObservableObject {
@Published var title:String = ""
}