Publishers.CombineLatest in SwiftUI

I could do something like the following.

class ValidateLogin {
	var good: Bool = false
	let user: String
	let pass: String
	init(user: String, pass: String) {
		self.user = user
		self.pass = pass
	}
	func validateMe() -> Bool {
		if user.count > 3 && pass.count > 3 {
			good = true
		}
		return good
	}
}

struct ContentView: View {
	@State var userText: String = ""
	@State var passText: String = ""
	@State var canSave: Bool = false
	
	var body: some View {
		ZStack {
			VStack {
				TextField("Username", text: $userText) {
					
				}.onChange(of: userText) { newValue in
					let validateLogin = ValidateLogin(user: userText, pass: passText)
					canSave = validateLogin.validateMe()
				}
				SecureField("Password", text: $passText) {
					
				}.onChange(of: passText) { newValue in
					let validateLogin = ValidateLogin(user: userText, pass: passText)
					canSave = validateLogin.validateMe()
				}
			}.padding(.horizontal, 20.0)
		}.onAppear {
			//Publishers.CombineLatest($userText, $passText)
			
		}
	}
}

The code above doesn't involve Combine at all. I want to do it in a Combine way.

To utilize Combine well, you may need to know what are (or should be or can be) publisher. @State variables cannot be publishers without some additional code.

To make publishers easily, you can work with ObservableObject with @Published variables:

import SwiftUI
import Combine

class ValidateLogin {
    let user: String
    let pass: String
    init(user: String, pass: String) {
        self.user = user
        self.pass = pass
    }
    
    func validateMe() -> Bool {
        return user.count > 3 && pass.count > 3
    }
}

class MyContent: ObservableObject {
    @Published var userText: String = ""
    @Published var passText: String = ""
}

struct ContentView: View {
    @StateObject var content = MyContent()
    @State var canSave: Bool = false
    @State var contentSubscriber: AnyCancellable?
    
    var body: some View {
        ZStack {
            VStack {
                TextField("Username", text: $content.userText) {
                }
                SecureField("Password", text: $content.passText) {
                }
            }.padding(.horizontal, 20.0)
        }.onAppear {
            self.contentSubscriber = self.content.$userText
                .combineLatest(content.$passText)
                .sink {userText, passText in
                    let validateLogin = ValidateLogin(user: userText, pass: passText)
                    self.canSave = validateLogin.validateMe()
                }
        }
    }
}

I guess ObservableObject is a ticket to using Combine in SwiftUI. So I can write the following.

import SwiftUI
import Combine

struct ContentView: View {
	@State var cancellables = Set<AnyCancellable>()
	@StateObject var login = Login()
	@State var canSave: Bool = false
	
	var body: some View {
		VStack {
			Text("Login")
			TextField("Enter username", text: $login.user)
			TextField("Enter password", text: $login.pass)
			Button("Save") {
				
			}
			.foregroundColor(canSave ? Color.orange : Color.gray)
			.font(.system(size: 40.0))
			.disabled(!canSave)
		}
		.padding(.horizontal, 40.0)
		.onAppear {
			Publishers.CombineLatest(login.$user, login.$pass)
				.sink { completion in
					print(completion)
				} receiveValue: { (result0, result1) in
					let bool = (result0.count > 3 && result1.count > 3)
					canSave = bool
				}.store(in: &cancellables)
		}
	}
}

class Login: ObservableObject {
	@Published var user: String = ""
	@Published var pass: String = ""
}

This is really good stuff.