How to Build A SwiftUI App With Firebase

In this article we take a look at how to integrate Google Sign In and Firebase. We will use SwiftUI for this project. The full source code for this project can be found here.

&amp;#x5C;
The app won&amp;#x27;t have much UI this time around, since most of the heavy lifting will be done by Google&amp;#x27;s own log in UI. We will just add a simple &amp;quot;Log in with Google&amp;quot; button on the screen and when its tapped, should take the user to the Google Sign In UI.

&amp;#x5C;
However, let&amp;#x27;s first set up Firebase and Google Sign In:

# 1. Setting up Firebase Project:

Head over to [Firebase.com](http:&amp;#x2F;&amp;#x2F;Firebase.com) and create a new account. Once logged in, create a new project in the Firebase Console.

* Head over to [Firebase.com](http:&amp;#x2F;&amp;#x2F;Firebase.com) and create a new account or log in.
* Create a new project in Firebase Console
* Once a new project is created, click Authentication.
* Select &amp;quot;Get Started&amp;quot; and then make sure you enable &amp;quot;Google Sign In&amp;quot; under sign-in methods.

  &amp;#x5C;

Next, we will add our iOS app with the Firebase console. Here is how it goes:

* Head over to &amp;quot;Project Overview&amp;quot; and select &amp;quot;Add iOS App&amp;quot;.
* This will ask you for your iOS app bundle ID. You can get this ID from the Xcode, select your Target &amp;gt; General &amp;gt; Bundle Identifier
* Next, download the configuration file generated at the next step to your computer (GoogleService-Info.plist) - we will simple drag and drop this .plist file in the root folder of our Xcode Project

Next we will need to install Firebase SDK. If you don&amp;#x27;t have Firebase already install then you have one of two ways. You can use CocoaPods or Swift Package Manager. I used Swift Package Manager to install SDK on my Xcode.


Here is how to do this:

* In Xcode go to File &amp;gt; Swift Packages &amp;gt; Add Package Dependency…
* You will see a prompt appear, please add this link there:
  &amp;lt;https:&amp;#x2F;&amp;#x2F;github.com&amp;#x2F;firebase&amp;#x2F;firebase-ios-sdk.git&amp;gt;
* Select the version of Firebase you would like to use. Make sure it&amp;#x27;s the latest one.
* Choose the Firebase products you would like to install.

&amp;#x5C;
# 2. Setting up Google Sign In:

Next, we will install Google Sign in SDK. We can do this in one of two ways by either using CocoaPods or using Swift Package Manager. Let&amp;#x27;s use Swift Package Manager. Here is how:

* In Xcode go to File &amp;gt; Swift Packages &amp;gt; Add Package Dependency…
* You will see a prompt appear, please add this link there:
  &amp;lt;https:&amp;#x2F;&amp;#x2F;github.com&amp;#x2F;google&amp;#x2F;GoogleSignIn-iOS&amp;gt;
* Click Add Package
* &amp;#x5C;

And that&amp;#x27;s it. Now we have both Firebase and Google Sign In SDKs. Next, in Xcode head over to the &amp;#96;GoogleService-Info.plist&amp;#96; file that you just dragged into Xcode. and select the URL in front of &amp;#96;Reverse_Client_ID&amp;#96;. Copy this URL and then do this:

* In the left panel of Xcode, click on the file with name of the your project. This is usually the first file.
* Click the file under &amp;#96;Targets&amp;#96; and then click &amp;#96;Info&amp;#96;
* Expand &amp;#96;URL Types&amp;#96; and click on the plus button to add a new URL type property.
* Paste the &amp;#96;Reverse_Client_ID&amp;#96; in the &amp;#96;URL schemes&amp;#96; text field.

&amp;#x5C;
# Implementation:

Now we are all set with the prerequisites. Now create an &amp;#96;AppDelegate&amp;#96; file and add the following code:

&amp;#96;&amp;#96;&amp;#96;javascript
import UIKit
import Firebase
import GoogleSignIn


class AppDelegate: NSObject, UIApplicationDelegate {
    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey : Any]? = nil) -&amp;gt; Bool {
        FirebaseApp.configure()
        return true
    }

    func application(_ application: UIApplication, open url: URL, options: [UIApplication.OpenURLOptionsKey: Any]) -&amp;gt; Bool {
      return GIDSignIn.sharedInstance.handle(url)
    }
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
First of all, we are just importing the &amp;#96;Firebase&amp;#96; and &amp;#96;GoogleSignIn&amp;#96; modules. Then in &amp;#96;appdidfinishLaunching&amp;#96; method, we are configuring Firebase by adding the code &amp;#96;Firebase.confgure()&amp;#96;. Next, we are going to link Google Sign in by adding another method which returns a &amp;#96;GIDSignIn shared instance&amp;#96;.

In the &amp;#96;.app&amp;#96; file please add the following code in order to link the new &amp;#96;AppDelegate&amp;#96; file:

&amp;#96;&amp;#96;&amp;#96;javascript
@main
struct GoogleSignInFirebaseApp: App {
    @UIApplicationDelegateAdaptor(AppDelegate.self) var appDelegate &amp;#x2F;&amp;#x2F;add this line

    var body: some Scene {
        WindowGroup {
            ContentView()
        }
    }
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
Now, we just need to implement the Google Sign in call back. Let&amp;#x27;s create a &amp;#96;LoginView.swift&amp;#96; file add the following code:

&amp;#96;&amp;#96;&amp;#96;javascript
struct LoginView: View {
    @AppStorage(&amp;quot;loginStatus&amp;quot;) var loginStatus = false &amp;#x2F;&amp;#x2F;1
    @State var presentSheet: Bool = false &amp;#x2F;&amp;#x2F; 2

    var body: some View {

        
        ZStack {
          &amp;#x2F;&amp;#x2F;Just a simple button when tapped invokes signInWithGoogle method
            Button {
                signInWithGoogle()
            } label: {
                Text(&amp;quot;Log In using Google&amp;quot;)
                    .padding()
                    .background(Color.blue)
                    .cornerRadius(20)
                    .foregroundColor(Color.white)
            }
        }
        &amp;#x2F;&amp;#x2F;Presents HomeView modally
        .fullScreenCover(isPresented: $presentSheet) {
                HomeView()
        }


    }

    &amp;#x2F;&amp;#x2F; The main deal...

    func signInWithGoogle() {
        guard let clientID = FirebaseApp.app()?.options.clientID else { return }

        &amp;#x2F;&amp;#x2F; Create Google Sign In configuration object.
        let config = GIDConfiguration(clientID: clientID)

        &amp;#x2F;&amp;#x2F; Start the sign in flow!
        GIDSignIn.sharedInstance.signIn(with: config, presenting: getRootViewController()) {  user, error in

          if let error = error {
            print(error)
            return
          }

          guard let authentication = user?.authentication,
                let idToken = authentication.idToken
          else {
            return
          }

          let credential = GoogleAuthProvider.credential(withIDToken: idToken,
                                                         accessToken: authentication.accessToken)

            Auth.auth().signIn(with: credential) { result, err in
                if let err = error {
                  print(err)
                  return
                }

                guard let user = result?.user else { return }

                print(user.displayName ?? &amp;quot;Success!&amp;quot;)
                self.presentSheet = true
                withAnimation {
                    self.loginStatus = true
                }

            }
        }
    }

}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
Let&amp;#x27;s go over in detail what is going on in &amp;#96;signInWithGoogle()&amp;#96; method. Initially, we are getting the &amp;#96;client ID&amp;#96; from Firebase, and then creating a Google Sign In &amp;#96;configuration&amp;#96; object using the &amp;#96;clientID&amp;#96;. Then once we have that we will start the sign in flow. We call the &amp;#96;GIDSignIn.sharedInstance.signIn&amp;#96; method which takes in the &amp;#96;configuration&amp;#96; object, and the root view controller. To extract the &amp;#96;rootViewController&amp;#96; please use the following extension on &amp;#96;View&amp;#96;:

&amp;#x5C;
&amp;#96;&amp;#96;&amp;#96;javascript
extension View {
    func getRootViewController() -&amp;gt; UIViewController {
        guard let screen = UIApplication.shared.connectedScenes.first as? UIWindowScene else {
            return .init()
        }

        guard let root = screen.windows.first?.rootViewController else {
            return .init()
        }

        return root

    }
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
The &amp;#96;GIDSignIn&amp;#96; method requires &amp;#96;rootViewController&amp;#96; so that it can present it&amp;#x27;s own view controller which presents the Google Sign In UI. Once the user signs in to the Google account and is successful in doing so, the callback returns with &amp;#96;error&amp;#96; and &amp;#96;result&amp;#96;. If there is no error present, we get user object with authentication id token. We use this authorization id token to create a credential. We will now use this credential to create a new user and sign into Firebase authentication using &amp;#96;Auth.auth().signin()&amp;#96; method. This method returns an error and result. If there is no error, we can get the user from the result object and toggle &amp;#96;presentSheet&amp;#96; boolean to true which will show the &amp;#96;HomeView&amp;#96;.

&amp;#x5C;
Also, here we are using &amp;#96;@AppStorage&amp;#96; property wrapper which acts like &amp;#96;UserDefaults&amp;#96; and saves the state of the user. So since we just signed in successfully to Firebase using Google Sign in, we will make &amp;#96;loginStatus&amp;#96; which is an &amp;#96;@AppStorage&amp;#96; variable to &amp;#96;true&amp;#96;. We will use this to do login persistence. 

&amp;#x5C;
Now, in &amp;#96;HomeView.swift&amp;#96; file, lets add the following code:

&amp;#x5C;
&amp;#96;&amp;#96;&amp;#96;javascript
import SwiftUI
import Firebase
import GoogleSignIn

struct User {
    var id: String = &amp;quot;&amp;quot;
    var name: String = &amp;quot;&amp;quot;
    var email: String = &amp;quot;&amp;quot;

}

struct HomeView: View {
    @State var user = User()
    @AppStorage(&amp;quot;loginStatus&amp;quot;) var loginStatus = false
    var body: some View {
        VStack(spacing: 20) {
            Text(&amp;quot;Welcome,&amp;#x5C;(user.name)&amp;quot;)
                .onAppear {
                    guard let user = Auth.auth().currentUser else { return }
                    self.user = User(id: user.uid, name: user.displayName ?? &amp;quot;&amp;quot;, email: user.email ?? &amp;quot;&amp;quot;)
            }

            Button {
                GIDSignIn.sharedInstance.signOut()
                try? Auth.auth().signOut()

                withAnimation {
                    self.loginStatus = false
                }
            } label: {
                Text(&amp;quot;Log Out&amp;quot;)
            }

        }
    }
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
Here, we when the view appears, we are using the Firebase&amp;#x27;s &amp;#96;currentUser&amp;#96; method to get the logged in user info and then creating a &amp;#96;User&amp;#96; object and then showing the &amp;#96;user.displayName&amp;#96; in the &amp;#96;Text&amp;#96; view. Also we have implemented a Log Out button which when pressed simply logs out the user from Google and Firebase. And observe, that we again changing the &amp;#96;loginStatus&amp;#96; variable to &amp;#96;false&amp;#96;.

&amp;#x5C;
Now, in the &amp;#96;ContentView.swift&amp;#96; file add the following code:

&amp;#96;&amp;#96;&amp;#96;javascript
struct ContentView: View {
    @AppStorage(&amp;quot;loginStatus&amp;quot;) var loginStatus = false
    var body: some View {
        if loginStatus {
            HomeView()
        }else {
            LoginView()
        }

    }
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
We are checking the &amp;#96;loginStatus&amp;#96;, and if it is &amp;#96;false&amp;#96;, then we show the &amp;#96;LogInView&amp;#96; else we show the &amp;#96;HomeView&amp;#96;.

You can refer to our [Firebase Authentication with Email and Password](https:&amp;#x2F;&amp;#x2F;dopebase.com&amp;#x2F;firebase-swiftui) tutorial to know more about how to save  User’s data (name, email, id) in a &amp;#96;Firestore&amp;#96; database and then retrieving it by using &amp;#96;user.uid&amp;#96; to query the database.

&amp;#x5C;


Google Sign In and Firebase Authentication using SwiftUI

Today in this article we will take a look at how to integrate Sign IN with Apple with Firebase Auth. We will use SwiftUI to design the UI of the app.
You can download the source code of this app here.

&amp;#x5C;
The app won&amp;#x27;t have much UI. We will just add a simple &amp;quot;Sign in with Apple&amp;quot; button on the screen and when its tapped should ask the user for Face ID&amp;#x2F;Passcode and then take user to Home view. We will add persistent login as well. So first let&amp;#x27;s go ahead and set up the Firebase console, and Xcode for the project.

&amp;#x5C;
&amp;#x5C;
# 1. Setting up Firebase Project:

Head over to [Firebase.com](http:&amp;#x2F;&amp;#x2F;Firebase.com) and create a new account. Once logged in, create a new project in the Firebase Console.

* Head over to [Firebase.com](http:&amp;#x2F;&amp;#x2F;Firebase.com) and create a new account or log in.
* Create a new project in Firebase Console
* Once a new project is created, click Authentication.
* Select &amp;quot;Get Started&amp;quot; and then make sure you enable &amp;quot;Apple&amp;quot; under sign-in methods.

Next, we will add our iOS app with the Firebase console. Here is how it goes:

* Head over to &amp;quot;Project Overview&amp;quot; and select &amp;quot;Add iOS App&amp;quot;.
* This will ask you for your iOS app bundle ID. You can get this ID from the Xcode, select your Target &amp;gt; General &amp;gt; Bundle Identifier
* Next, download the configuration file generated at the next step to your computer (GoogleService-Info.plist) - we will simple drag and drop this .plist file in the root folder of our Xcode Project

Next we will need to install Firebase SDK. If you don&amp;#x27;t have Firebase already install then you have one of two ways. You can use CocoaPods or Swift Package Manager. I used Swift Package Manager to install SDK on my Xcode.
Here is how to do this:

* In Xcode go to File &amp;gt; Swift Packages &amp;gt; Add Package Dependency…
* You will see a prompt appear, please add this link there:
  &amp;lt;https:&amp;#x2F;&amp;#x2F;github.com&amp;#x2F;firebase&amp;#x2F;firebase-ios-sdk.git&amp;gt;
* Select the version of Firebase you would like to use. Make sure it&amp;#x27;s the latest one.
* Choose the Firebase products you would like to install.

&amp;#x5C;
# 2. Setting up Xcode:

In Xcode head over to &amp;quot;Signing and Capabilities&amp;quot;, click on the &amp;quot;+&amp;quot; icon on the top bar of Xcode and select &amp;quot;Sign in with Apple&amp;quot;. That&amp;#x27;s it.

&amp;#x5C;
For this project we will have 3 views, the &amp;#96;LoginView,&amp;#96; a &amp;#96;HomeView&amp;#96; and a &amp;#96;ContentView&amp;#96;. Let&amp;#x27;s create the &amp;#96;LoginView&amp;#96; first.  First import &amp;#96;AuthenticationServices&amp;#96; module in &amp;#96;LoginView.swift&amp;#96; file. Next, add the &amp;#96;Sign in with Apple&amp;#96; button:

&amp;#x5C;
&amp;#96;&amp;#96;&amp;#96;javascript
import SwiftUI
import AuthenticationServices
struct LoginView: View {
    @StateObject var loginData = LoginViewModel()
    var body: some View {
        SignInWithAppleButton { request in
            &amp;#x2F;&amp;#x2F; Code goes here 1
        } onCompletion: { (result) in
            switch result {
            case .success(let user):
                print(&amp;quot;Login with Firebase&amp;quot;)
                &amp;#x2F;&amp;#x2F; code goes here 2

            case .failure(let error):
                print(error.localizedDescription)

            }
        }.frame(height: 55)
        .clipShape(Capsule())
        .padding(.horizontal, 30)
    }
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
Now before we start, we need to comply with Apple&amp;#x27;s anonymized data requirements as well as need to implement some crypto security checks. First create a new file and call it &amp;#96;LoginViewModel&amp;#96;. In the &amp;#96;LoginViewModel&amp;#96; we will have a published property called &amp;#96;nonce&amp;#96;. A &amp;#96;nonce&amp;#96; is a random string which is generated every time a sign in request is made. To generate this &amp;#96;nonce&amp;#96;, please import &amp;#96;CryptoKit&amp;#96; in &amp;#96;LoginViewModel&amp;#96; file.

&amp;#x5C;
Then, we will create a helper function and we will call it &amp;#96;randomNonceString&amp;#96;. Here is the implementation of the function:

&amp;#96;&amp;#96;&amp;#96;javascript
func randomNonceString(length: Int = 32) -&amp;gt; String {
 precondition(length &amp;gt; 0)
 let charset: [Character] =
   Array(&amp;quot;0123456789ABCDEFGHIJKLMNOPQRSTUVXYZabcdefghijklmnopqrstuvwxyz-._&amp;quot;)
 var result = &amp;quot;&amp;quot;
 var remainingLength = length

 while remainingLength &amp;gt; 0 {
   let randoms: [UInt8] = (0 ..&amp;lt; 16).map { _ in
     var random: UInt8 = 0
     let errorCode = SecRandomCopyBytes(kSecRandomDefault, 1, &amp;amp;random)
     if errorCode != errSecSuccess {
       fatalError(
         &amp;quot;Unable to generate nonce. SecRandomCopyBytes failed with OSStatus &amp;#x5C;(errorCode)&amp;quot;
       )
     }
     return random
   }

   randoms.forEach { random in
     if remainingLength == 0 {
       return
     }

     if random &amp;lt; charset.count {
       result.append(charset[Int(random)])
       remainingLength -= 1
     }
   }
 }

 return result
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
We will create another helper function called &amp;#96;sha256&amp;#96;, here is the implementation:

&amp;#96;&amp;#96;&amp;#96;javascript
func sha256(_ input: String) -&amp;gt; String {
 let inputData = Data(input.utf8)
 let hashedData = SHA256.hash(data: inputData)
 let hashString = hashedData.compactMap {
   String(format: &amp;quot;%02x&amp;quot;, $0)
 }.joined()

 return hashString
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
Now, back to the &amp;#96;LoginViewModel&amp;#96;, please add the following code:

&amp;#96;&amp;#96;&amp;#96;javascript
import SwiftUI
import CryptoKit
import AuthenticationServices
import Firebase

class LoginViewModel: ObservableObject {
    @Published var nonce = &amp;quot;&amp;quot;
    @AppStorage(&amp;quot;loginStatus&amp;quot;) var isLoggedIn = false
    func authenticate(credential: ASAuthorizationAppleIDCredential) {
        guard let token = credential.identityToken else {
            print(&amp;quot;Error: Token&amp;quot;)
            return
        }

        guard let tokenString = String(data: token, encoding: .utf8) else {
            print(&amp;quot;Error: token to string&amp;quot;)
            return
        }

        let firebaseCredential = OAuthProvider.credential(withProviderID: &amp;quot;apple.com&amp;quot;, idToken: tokenString, rawNonce: nonce)

        Auth.auth().signIn(with: firebaseCredential) { result, error in
            if let error = error {
                print(error.localizedDescription)
                return
            }

            print(&amp;quot;User logged in successfully&amp;quot;)
            withAnimation {
                self.isLoggedIn = true
            }
        }
    }
}

&amp;#x2F;&amp;#x2F;.... helper functions go here
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
In this &amp;#96;LoginViewModel&amp;#96;, when we create the &amp;#96;authenticate&amp;#96; subroutine, which takes &amp;#96;ASAuthorizationAppleIDCredential&amp;#96;, we will get the credential token which we will convert to string, and use that token string to then sign into Firebase. We also have an &amp;#96;@AppStorage&amp;#96; property which tracks the user&amp;#x27;s login status. Now let&amp;#x27;s call this &amp;#96;authenticate&amp;#96; subroutine of &amp;#96;LoginViewModel&amp;#96; from the &amp;#96;SignInWithAppleButton&amp;#x27;s&amp;#96; closure.

&amp;#x5C;
So back to &amp;#96;LoginView.swift&amp;#96; file, please add the following code in the closure:

&amp;#96;&amp;#96;&amp;#96;javascript
 struct LoginView: View {
    @StateObject var loginData = LoginViewModel()
    var body: some View {
        SignInWithAppleButton { request in
            loginData.nonce = randomNonceString()
            request.requestedScopes = [.email, .fullName]
            request.nonce = sha256(loginData.nonce)
        } onCompletion: { (result) in
            switch result {
            case .success(let user):
                print(&amp;quot;Login with Firebase&amp;quot;)
                guard let credential = user.credential as? ASAuthorizationAppleIDCredential else {
                    print(&amp;quot;Error with user credentials&amp;quot;)
                    return
                }
                loginData.authenticate(credential: credential)
            case .failure(let error):
                print(error.localizedDescription)

            }
        }.frame(height: 55)
        .clipShape(Capsule())
        .padding(.horizontal, 30)
    }
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
Here, we are generating a random &amp;#96;Nonce&amp;#96; string, and then passing the &amp;#96;nonce&amp;#96; as well as the &amp;#96;requestedScopes&amp;#96; to the request. The &amp;#96;requestedScopes&amp;#96;  include email and fullName , if the user chooses to provide this data. The user can choose to hide the fullName and email, in which case an email address of such domain &amp;#96;privaterelay.appleid.com&amp;#96; is provided. The random &amp;#96;nonce&amp;#96; string is generated every time a request is made and then returned to us in terms of an &amp;#96;identityToken&amp;#96;  through &amp;#96;ASAuthorizationAppleIDCredential&amp;#96; object which we use in the &amp;#96;LoginViewModel&amp;#96; code above. Then this identityToken is converted to a string, compared with the raw nonce which we generated earlier and if all is good give us an &amp;#96;OAuthProvider&amp;#96; credential which is used to sign in to Firebase.

&amp;#x5C;
And that is pretty much it. Now let&amp;#x27;s implement some more UI features as well sign out button. Implement the following code in &amp;#96;HomeView.swift&amp;#96;:

&amp;#96;&amp;#96;&amp;#96;javascript
import SwiftUI
import Firebase

struct HomeView: View {
    @AppStorage(&amp;quot;loginStatus&amp;quot;) var isLoggedIn = true
    var body: some View {

        VStack {
            Text(&amp;quot;Home View&amp;quot;)
            Button {
                DispatchQueue.global(qos: .background).async {
                    try? Auth.auth().signOut()
                }

                withAnimation {
                    isLoggedIn = false
                }
            } label: {
                Text(&amp;quot;Log Out&amp;quot;)
            }

        }

    }
}
&amp;#96;&amp;#96;&amp;#96;

Here we have a button which when tapped signs out the user from Firebase Auth, and also changes the &amp;#96;isLoggedIn&amp;#96; status to false. Then, in &amp;#96;ContentView.swift&amp;#96; file this is where we are deciding which view to show:  the &amp;#96;HomeView&amp;#96; or &amp;#96;LogInView&amp;#96;. Implement the following code in &amp;#96;ContentView&amp;#96;:

&amp;#96;&amp;#96;&amp;#96;javascript
struct ContentView: View {
    @AppStorage(&amp;quot;loginStatus&amp;quot;) var isLoggedIn = false
    var body: some View {
        if isLoggedIn {
            HomeView()
        }else {
            LoginView()
        }

    }
}
&amp;#96;&amp;#96;&amp;#96;

&amp;#x5C;
So, whenever the &amp;#96;@AppStorage&amp;#96; property changes, the &amp;#96;ContentView&amp;#96; is refreshed and the appropriate view is shown.

How to implement Firebase Auth with Sign in with Apple using SwiftUI

Swift now supports asynchronous (async) functions, enabling us to run complicated asynchronous code almost as if it were synchronous thanks to SE-0296. As in other languages like C# and JavaScript, this is accomplished in two steps: first, async functions are identified using the new &#x5C;&#96;&#96;async&#96;&#x5C;&#96; keyword, and then they are called with the &#96;await&#96; keyword. Let’s take a look at a few code examples to understand exactly how to use **await** and **async** in Swift.

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Let’s start with a quick example so you can see what the syntax for **async** and **await** looks like in **Swift** - most of the code should be self-explanatory.

## Async Await in Swift - Example

&#96;&#96;&#96;javascript
func fetchSomethingFromServer() async -&gt; [Double] {
    &#x2F;&#x2F; This can be a network request, a file data read, anything expensive really.
    (1...10000).map { _ in Double.random(in: -10...30) }
}

func average(for results: [Double]) async -&gt; Double {
    let sum = results.reduce(0, +)
    let avg = sum &#x2F; Double(results.count)
    return avg
}

func upload(result: Double) async -&gt; String {
    &#x2F;&#x2F; upload something to a server, this can be any expensive operation
    return &quot;Done&quot;
}
&#96;&#96;&#96;

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We’ve implemented 3 different **async** functions - notice the &#96;async&#96; keyword in their signature - this means that the blocks are dispatched to a background queue, and are run asynchronously.

Let’s see now how we can call these methods in order to actually process the results, and not just obtain a reference to the execution promise.

&#96;&#96;&#96;javascript
func processEverything() async {
    let results = await fetchSomethingFromServer()
    let avg = await average(for: results)
    let response = await upload(result: avg)
    print(&quot;Server response: &#x5C;(response)&quot;)
}
&#96;&#96;&#96;

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As you can see, all of the indenting and closures have been removed, leaving what is frequently referred to as &quot;straight-line code&quot;; except from the await keywords, it resembles synchronous code. Because the execution is linear, it is simple to understand and reason about. While we&#x27;re still doing occasionally difficult asynchronous jobs, it will be simpler to understand asynchronous programming, as using **await** &#x2F; **async** in Swift is clearly a lot more readable.

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There are a few simple, clear guidelines that govern how async functions operate:

* Swift will generate an error if synchronized functions attempt to invoke async functions directly because that wouldn&#x27;t make sense.
* Async functions have the ability to call other async functions, but they can also, if necessary, call synchronous functions.
* Swift will favor the function that best fits the current context if you have async and synchronous functions that can be called in the same way. If the call site is now async, Swift will call the async function; if not, it will call the synchronous function.

## Calling Await from Synchronous Functions

You cannot use await in a synchronous environment. To be able to leverage async &#x2F; await from a synchronous method, you can use &#96;Task.init&#96; like in the example below:

&#96;&#96;&#96;javascript
func fetchSomeData() {
        Task.init {
            do {
                self.results = try await fetchResults()
            } catch {
                &#x2F;&#x2F; .. handle error
            }
        }
    }
&#96;&#96;&#96;

## Async &#x2F; Await with Try &#x2F; Catch

**Async functions** and initializers now have the ability to throw errors when necessary thanks to the advent of &#96;async&#96;&#x2F;&#96;await&#96;, which perfectly complements &#96;try&#96;&#x2F;&#96;catch&#96;. The one exception is that Swift mandates a specific order for the keywords, and between call site and function, that order is inverted.

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Here’s a code example of how to use async await in Swift within a try - catch block:

&#96;&#96;&#96;javascript
do {
    let data = try await fetchData()
    let processedData = try await process(data)
    print(&quot;Fetched &#x5C;(processedData.count) results.&quot;)
} catch {
    print(&quot;Fetching data failed with error &#x5C;(error)&quot;)
}
&#96;&#96;&#96;

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This is pretty much everything you need to know about async await in Swift. If you think there’s anything we missed, please let us know.  Additionally, if you found this tutorial helpful, please share it on Twitter, to help us spread the word. Thanks!

Async Await in Swift with Code Examples

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