如何根据用户输入使用新的谓词重新运行@FetchRequest？

struct ContentView: View {
    @Environment(\.managedObjectContext) private var viewContext
    @Environment(\.presentationMode) private var presentationMode
    
    @FetchRequest(
        sortDescriptors: [NSSortDescriptor(keyPath: \Item.timestamp, ascending: true)],
        animation: .default)
    private var items: FetchedResults<Item>
    
    @State private var userInput: String = ""
    @State private var predicate: NSPredicate?
    
    var body: some View {
        VStack {
            TextField("Enter search term", text: $userInput)
                .padding()
                .onChange(of: userInput) { newValue in
                    updatePredicate()
                }
            
            List {
                ForEach(items) { item in
                    Text(item.name ?? "Unknown")
                }
            }
        }
        .onAppear {
            updatePredicate()
        }
    }
    
    private func updatePredicate() {
        if userInput.isEmpty {
            predicate = nil
        } else {
            predicate = NSPredicate(format: "name CONTAINS[c] %@", userInput)
        }
    }
}