Fixed a bug with no view due to the SwiftUI view lifecycle.

[HanweeeeLee]

Problem 1

as-is)
The Partial Sheet does not work in the following code:

struct ContentView: View {
  var body: some View {
    VStack {
      
    }
    .partialSheet(isPresented: .constant(true)) {
      Text("Hello World")
    }
    .attachPartialSheetToRoot()
  }
}

The reason it doesn’t work can be identified in this code:

struct PSManagerWrapper<Parent: View, SheetContent: View>: View {
    ...
    var body: some View {
        parent
            .onChange(of: isPresented, perform: {_ in updateContent() })
    }
    ...
}

Since 'updateContent()' only triggers when the value of 'isPresented' changes, if the initial value is true, the screen does not update.

to-be)
Modifying the code as below allows the initial value to be reflected correctly:

struct PSManagerWrapper<Parent: View, SheetContent: View>: View {
    ...
    var body: some View {
        parent
            .onChange(of: isPresented, perform: {_ in updateContent() })
            .task { updateContent() }
    }
    ...
}

Problem 2

as-is)
The view disappears when the “Source of Truth” value changes, as shown below:

class SampleModel: ObservableObject {
  @Published var candidateChannelList: [String] = []
  
  func updateChannels() {
    candidateChannelList = ["Channel 1", "Channel 2", "Channel 3"]
  }
}

struct ContentView: View {
  @State private var isSheetPresented = false
  @StateObject private var sampleModel = SampleModel()
  
  var body: some View {
    VStack {
      Button("Show Partial Sheet") {
        isSheetPresented = true
      }
    }
    .partialSheet(isPresented: $isSheetPresented) {
      FeedChannelSelectorView(sampleModel: sampleModel, isPresented: $isSheetPresented)
    }
    .attachPartialSheetToRoot()
  }
}

struct FeedChannelSelectorView: View {
  @ObservedObject var sampleModel: SampleModel
  @Binding var isPresented: Bool
  
  var body: some View {
    VStack {
      HStack {
        Spacer()
        Button("Close") {
          isPresented = false
        }
        .padding()
      }
      
      Button(action: {
        sampleModel.updateChannels()
      }, label: {
        Text("RequestUpdate")
      })
      
      Text("Select a Channel")
        .font(.title)
        .padding(.bottom, 10)
      
      List(sampleModel.candidateChannelList, id: \.self) { channel in
        Text(channel)
          .onTapGesture {
            print("\(channel) selected")
            isPresented = false
          }
      }
    }
    .padding()
    .background(Color.white)
    .cornerRadius(10)
  }
}

We can see why the view disappears by looking at the following code:

public class PSManager: ObservableObject {
    
    /// Published var to present or hide the partial sheet
    @Published var isPresented: Bool = false {
        didSet {
            if !isPresented {
                DispatchQueue.main.asyncAfter(deadline: .now() + 0.35) { [weak self] in
                    self?.content = EmptyView().eraseToAnyView()
                    self?.onDismiss = nil
                }
            }
        }
    }
    ...

The PSManager class has its own @published property, isPresented. The Partial Sheet operates based on this isPresented value. When attachPartialSheetToRoot() is called, a new instance of PSManager is created:

public extension View {
    ...
    func attachPartialSheetToRoot() -> some View {
        let sheetManager: PSManager = PSManager()
        return self
            .modifier(PartialSheet())
            .environmentObject(sheetManager)
    }
    ...

Each time the “Source of Truth” changes, the view seems to be redrawn, causing a new PSManager to be created.

to-be)
To solve this, I modified attachPartialSheetToRoot() to allow an externally managed PSManager instance. Although this is not ideal, it provides a temporary solution:

public extension View {
    ...
    func attachPartialSheetToRoot(manager: PSManager? = nil) -> some View {
        let manager = {
           if let manager {
               return manager
           } else {
               return PSManager()
           }
        }() 
        
        let sheetManager: PSManager = manager
        
        return self
            .modifier(PartialSheet())
            .environmentObject(sheetManager)
    }
    ...

This requires making PSManager public to manage its instances externally.

public class PSManager: ObservableObject {
    ...
    public init() {
        content = EmptyView().eraseToAnyView()
        slideAnimation = PSSlideAnimation()
    }
    ...
}

Then, the ContentView is updated as follows:

class SampleModel: ObservableObject {
  @Published var candidateChannelList: [String] = []
  
  func updateChannels() {
    candidateChannelList = ["Channel 1", "Channel 2", "Channel 3"]
  }
}

struct ContentView: View {
  @State private var isSheetPresented = false
  @StateObject private var sampleModel = SampleModel()
  @StateObject private var psManager = PSManager()
  
  var body: some View {
    VStack {
      Button("Show Partial Sheet") {
        isSheetPresented = true
      }
    }
    .partialSheet(isPresented: $isSheetPresented) {
      FeedChannelSelectorView(sampleModel: sampleModel, isPresented: $isSheetPresented)
    }
    .attachPartialSheetToRoot(manager: psManager)
  }
}

struct FeedChannelSelectorView: View {
  @ObservedObject var sampleModel: SampleModel
  @Binding var isPresented: Bool
  
  var body: some View {
    VStack {
      HStack {
        Spacer()
        Button("Close") {
          isPresented = false
        }
        .padding()
      }
      
      Button(action: {
        sampleModel.updateChannels()
      }, label: {
        Text("Refresh")
      })
      
      Text("Select a Channel")
        .font(.title)
        .padding(.bottom, 10)
      
      List(sampleModel.candidateChannelList, id: \.self) { channel in
        Text(channel)
          .onTapGesture {
            print("\(channel) selected")
            isPresented = false
          }
      }
    }
    .padding()
    .background(Color.white)
    .cornerRadius(10)
  }
}

If you apply the above modifications, it should work as intended. Let me know if you have suggestions for a better approach!