CombineLatest.swift

import UIKit
import RxSwift
import RxCocoa
import Alamofire

class ViewController: UIViewController {
    let disposeBag = DisposeBag()
    @IBOutlet weak var firstname: UITextField!
    @IBOutlet weak var lastname: UITextField!
    @IBOutlet weak var employeeId: UITextField!
    var firstNameValid : Observable<Bool>!
    var lastNameValid : Observable<Bool>!
    var employeeValid : Observable<Bool>!

    @IBOutlet weak var button: UIButton!
    
    override func viewDidLoad() {
        super.viewDidLoad()
        firstNameValid = firstname.rx.text
            .orEmpty.map { !$0.isEmpty
        }
        lastNameValid = lastname.rx.text
            .orEmpty.map { !$0.isEmpty
            }
        employeeValid = employeeId.rx.text
            .orEmpty.map { !$0.isEmpty
            }
        let isButtonEnabled = Observable.combineLatest(firstNameValid, lastNameValid,employeeValid) { $0 && $1 && $2}
        isButtonEnabled.bindTo(button.rx.enabled)
    }
}