使用RXSwift进行SwiftUI表单验证？

import SwiftUI
import RxSwift
import RxCocoa

class FormViewModel {
    let username = BehaviorRelay<String>(value: "")
    let password = BehaviorRelay<String>(value: "")
    let confirmPassword = BehaviorRelay<String>(value: "")
    
    var isUsernameValid: Observable<Bool> {
        return username.asObservable()
            .map { $0.count >= 6 }
    }
    
    var isPasswordValid: Observable<Bool> {
        return password.asObservable()
            .map { $0.count >= 8 }
    }
    
    var doPasswordsMatch: Observable<Bool> {
        return Observable.combineLatest(password.asObservable(), confirmPassword.asObservable())
            .map { $0 == $1 }
    }
    
    var isFormValid: Observable<Bool> {
        return Observable.combineLatest(isUsernameValid, isPasswordValid, doPasswordsMatch)
            .map { $0 && $1 && $2 }
    }
}

struct ContentView: View {
    @ObservedObject var viewModel = FormViewModel()
    
    var body: some View {
        VStack {
            TextField("Username", text: $viewModel.username.value)
                .padding()
            
            SecureField("Password", text: $viewModel.password.value)
                .padding()
            
            SecureField("Confirm Password", text: $viewModel.confirmPassword.value)
                .padding()
            
            Button("Sign Up") {
                // 处理注册逻辑
            }
            .disabled(!viewModel.isFormValid)
        }
        .padding()
    }
}