使用@State 变量不适用于从子视图更改 Body 中的视图 state

Question

Let's say in my iOS SwiftUI app there is a simple ContentView with two views inside.

The reference to ContentView is available to other parts of code.

From there the user wants to determine which of the two views are displayed, that is, one, none or both.

That code is something like

contentViewReference.setView1Visible(view1Visible:true) //or false

Here's the ContentView

struct ViewsState
{
    var view1Visible:Bool
    var view2Visible:Bool
    init(view1Visible:Bool,view2Visible:Bool)
       {
          self.view1Visible=view1Visible
          self.view2Visible=view2Visible
       }
 }

struct ContentView: View 
{ 
    @State private var viewsState:ViewsState=ViewsState(view1Visible:true,view2Visible:false)

    
    public func setView1Visible(view1Visible:Bool)
        {
          viewsState.view1Visible=view1Visible
        }

    public func setView2Visible(view2Visible:Bool)
        {
          viewsState.view2Visible=view2Visible
        }

    var body: some View 
    {
        if (viewsState.view1Visible) {View1}
        if (viewsState.view1Visible) {View2}
    }
}

but the views' visibility does never change, why?

I do not think I need Binding because the state "truth" is inside ContentView, but it is assigned through public funcs.

There is no parent View, the toggling code indeed is inside a menu that is part of View1.

But when calling

setView1Visible(view1Visible:false)

for example, there is no effect, View1 does not become hidden.

This is just a snippet of code. Real ContentView is slightly more elaborate, but the question does not change.

Answer 1

@P5music, there is not enough code to replicate your issue and investigate properly. Also I don't know how you get:

   contentViewReference.setView1Visible(view1Visible:true) 

Here are some observations regarding your code.

    @State private var viewsState:ViewsState(view1Visible:true,view2Visible:false)

should be

    @State var viewsState = ViewsState(view1Visible:true,view2Visible:false)

also you probably want:

    var body: some View 
{
    if (viewsState.view1Visible) {View1}
    if (viewsState.view2Visible) {View2}  // <--- here 
}

In addition, "...determine which of the two views are displayed", this means that every time you set "view1Visible" to some value, at the same time you also need to set "view2Visible" to the opposite.

Answer 2

class ViewsState: ObservableObject
{
    @Published var view1Visible:Bool
    @Published var view2Visible:Bool
    init(view1Visible:Bool,view2Visible:Bool)
    {
        self.view1Visible=view1Visible
        self.view2Visible=view2Visible
    }
    public func setView1Visible(view1Visible:Bool)
    {
        self.view1Visible = view1Visible
        view2Visible = !view1Visible
    }
    
    public func setView2Visible(view2Visible:Bool)
    {
        self.view2Visible = view2Visible
        view1Visible = !view2Visible
    }
}

struct ViewStateView: View {
    @StateObject private var viewsState: ViewsState = ViewsState(view1Visible:true,view2Visible:false)

    var body: some View
    {
        VStack{
            if (viewsState.view1Visible) {Text("View1")}
            if (viewsState.view2Visible) {Text("View2")}
            SomeOtherView().environmentObject(viewsState)
        }
    }
}
struct SomeOtherView: View {
    @EnvironmentObject var viewsState: ViewsState
    var body: some View
    {
        VStack{
            Text("SomeOtherView")
            Button("change state view 1", action: {
                viewsState.setView1Visible(view1Visible:false)
            })
            Button("change state view 2", action: {
                viewsState.setView2Visible(view2Visible:false)
            })
        }
        
    }
}
struct ViewStateView_Previews: PreviewProvider {
    static var previews: some View {
        ViewStateView()
    }

Answer 3

Assuming your "contentViewReference.setView1Visible(view1Visible:true)" works, the following test code seems to work:

import SwiftUI

@main
struct TestApp: App {
    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}

struct ViewsState{
    var view1Visible:Bool
    var view2Visible:Bool
    init(view1Visible:Bool, view2Visible:Bool){
        self.view1Visible = view1Visible
        self.view2Visible = view2Visible
    }
}

struct ContentView: View {
    @State var viewsState = ViewsState(view1Visible:true, view2Visible:false)
    
    public func setView1Visible(view1Visible:Bool){
        viewsState.view1Visible = view1Visible
        viewsState.view2Visible = !view1Visible
    }
    
    public func setView2Visible(view2Visible:Bool){
        viewsState.view2Visible = view2Visible
        viewsState.view1Visible = !view2Visible
    }
    
    var body: some View {
        VStack {
            Button("change view") {
                if viewsState.view1Visible {
                    setView1Visible(view1Visible: false)
                } else {
                    setView1Visible(view1Visible: true)
                }
            }
            if (viewsState.view1Visible) {View1()}
            if (viewsState.view2Visible) {View2()}
        }
    }
}

struct View1: View {
    var body: some View {
        Text("View1")
    }
}

struct View2: View {
    var body: some View {
        Text("View2")
    }
}