SwiftDataUIKit.swift

import SwiftUI
import SwiftData
import UIKit

@Model
class Item {
    var text: String = ""
    init(text: String) {
        self.text = text
    }
}

struct TextInputView: View {
    @Environment(\.modelContext) var modelContext
    @State private var textFieldText = ""
    
    var body: some View {
        TextField("Type here", text: $textFieldText)
            .textFieldStyle(RoundedBorderTextFieldStyle())
            .padding()
            .onSubmit {
                modelContext.insert(Item(text: textFieldText))
                textFieldText = ""
            }
    }
}

struct KeyboardAnchoredContainer<Content: View, Input: View>: UIViewControllerRepresentable {
    typealias ViewController = KeyboardAnchoredContainerViewController
    
    @ViewBuilder var content: () -> Content
    @ViewBuilder var input: () -> Input
    
    func makeUIViewController(context: Context) -> ViewController<Content, Input> {
        ViewController(content: content(), input: input())
    }
    func updateUIViewController(_ uiViewController: ViewController<Content, Input>, context: Context) {}
}

class KeyboardAnchoredContainerViewController<Content: View, Input: View>: UIViewController {
    
    var content: Content
    var input: Input
    
    init(content: Content, input: Input) {
        self.content = content
        self.input = input
        super.init(nibName: nil, bundle: nil)
    }
    
    required init?(coder: NSCoder) {
        fatalError("init(coder:) has not been implemented")
    }
    
    override func viewDidLoad() {
        setUpContent()
        setUpInput()
    }
    
    private func setUpContent() {
        let hostingView = UIHostingController(rootView: content)
        hostingView.view.translatesAutoresizingMaskIntoConstraints = false
        view.addSubview(hostingView.view)
        
        // Anchor content to top of keyboard layout
        NSLayoutConstraint.activate([
            hostingView.view.bottomAnchor.constraint(equalTo: view.keyboardLayoutGuide.topAnchor),
            hostingView.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            hostingView.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            hostingView.view.topAnchor.constraint(equalTo: view.topAnchor),
        ])
    }
    
    private func setUpInput() {
        let hostingView = UIHostingController(rootView: TextInputView())
        view.addSubview(hostingView.view)
        hostingView.view.translatesAutoresizingMaskIntoConstraints = false
        
        // Anchor input to top of keyboard layout
        NSLayoutConstraint.activate([
            hostingView.view.bottomAnchor.constraint(equalTo: view.keyboardLayoutGuide.topAnchor),
            hostingView.view.leadingAnchor.constraint(equalTo: view.leadingAnchor),
            hostingView.view.trailingAnchor.constraint(equalTo: view.trailingAnchor),
            hostingView.view.heightAnchor.constraint(equalToConstant: 46)
        ])
    }
}

struct ContentView: View {
    var body: some View {
        KeyboardAnchoredContainer {
            ItemListView()
        } input: {
            TextInputView()
        }
        // This is key, otherwise the text input taps into SwiftUI's keyboard safe area avoidance.
        .ignoresSafeArea(.keyboard)
    }
}

struct ItemListView: View {
    
    // Define the Query here so the view can update itself.
    @Query var items: [Item]
    
    var body: some View {
        ScrollView {
            VStack {
                ForEach(items) { item in
                    HStack {
                        Text(item.text)
                            .padding()
                        Spacer()
                    }
                }
            }
            // Inset content slightly to avoid overlap with text input.
            .padding(.bottom, 40)
        }
        .scrollDismissesKeyboard(.interactively)
        .scrollClipDisabled()
        .defaultScrollAnchor(.bottom)
    }
}

#Preview {
    ContentView()
        .modelContainer(for: Item.self, inMemory: true)
}