Update application code

Now that we have a GraphQL API to support access our data model from the cloud, let’s modify the application code to call the GraphQL endpoint instead of listing hard coded values.

At high level, here is how we gonna proceed

  • first, we’re going to add the pod dependency to access the AWS AppSync client library

  • the app sync client code is contained in AppDelegate class, as we did for authentication.

  • UserData class holds a hard code reference to the list of Landmarks loaded at application startup time. We are going to replace with an empty list ([]) and we’re going to add code to query the API and populate the list after sucesfull sign in.

Add the AWS AppSync client library

Edit $PROJECT_DIRECTORY/Podfile to add the AppSync dependency. Your Podfile must look like this (you can safely copy/paste the entire file from belowpwd):

# Uncomment the next line to define a global platform for your project
platform :ios, '13.0'

target 'Landmarks' do
  # Comment the next line if you don't want to use dynamic frameworks

  # Pods for Landmarks
  pod 'AWSMobileClient', '~> 2.12.0'      # Required dependency
  pod 'AWSAuthUI', '~> 2.12.0'            # Optional dependency required to use drop-in UI
  pod 'AWSUserPoolsSignIn', '~> 2.12.0'   # Optional dependency required to use drop-in UI
  pod 'AWSAppSync', '~> 2.15.0'           # For AppSync GraphQL API

In a Terminal, type the following commands to download and install the dependencies:

pod install --repo-update

After one minute, you shoud see the below:

Pod update

Modify UserData class

UserData holds a hard coded list of landmarks, loaded from a JSON files (Landmarks/Resources/landmarkData.json). The Landmarks/Models/Data.swift class loads the JSON file at application startup time using this line:

let landmarkData: [Landmark] = load("landmarkData.json")

Let’s replace UserData.swift with the below

See LICENSE folder for this sample’s licensing information.

A model object that stores app data.

import Combine
import SwiftUI

final class UserData: ObservableObject {
    @Published var showFavoritesOnly = false
    @Published var landmarks : [Landmark] = []
    @Published var isSignedIn : Bool = false

On line 13, we initialise the list of landmarks with an empty array, while preserving the type of the variable.

Add the generated code to the project

Thanks to the strongly typed nature of GraphQL, Amplify generated Swift code to access the data types, the queries and the mutations of the API. Remember? The file was generated when you last type amplify push. Now it’s time to add the generated file in your project. In the Finder, drag API.swift into Xcode under the Landmarks folder, where the rest of the code is. When the Options dialog box appears, do the following:

  • Clear the Copy items if needed check box.
  • Choose Create groups, and then choose Finish.

Add client code in the application delegate

We modify AppDelegate to add code to call the GraphQL API. You can safely copy/paste the entire file from below.

// Landmarks/AppDelegate.swift

import UIKit
import AWSMobileClient
import AWSAppSync

class AppDelegate: UIResponder, UIApplicationDelegate {

    public let userData = UserData()
    var appSyncClient: AWSAppSyncClient?

    func application(_ application: UIApplication, didFinishLaunchingWithOptions launchOptions: [UIApplication.LaunchOptionsKey: Any]?) -> Bool {
        //init appsync
        AWSMobileClient.default().addUserStateListener(self) { (userState, info) in
            // notify our subscriber the value changed
            self.userData.isSignedIn = AWSMobileClient.default().isSignedIn

            switch (userState) {
            case .guest:
                print("user is in guest mode.")
            case .signedOut:
                print("user just signed out")
                self.userData.landmarks = []
            case .signedIn:
                print("user just signed in.")
                print("username : \(String(describing: AWSMobileClient.default().username))")
                print("Loading data")

                AWSMobileClient.default().getUserAttributes(completionHandler: { (attributes, error) in
                    print("error : \(String(describing: error))")
                    print("attributes: \(String(describing: attributes))")
                    AWSMobileClient.default().getTokens({ (tokens, error) in
                        print("error : \(String(describing: error))")
                        print("token : \(String(describing: tokens))")
            case .signedOutUserPoolsTokenInvalid:
                print("need to login again.")

            case .signedOutFederatedTokensInvalid:
                print("user logged in via federation, but currently needs new tokens")

        AWSMobileClient.default().initialize { (userState, error) in

            // notify our subscriber the value changed
            self.userData.isSignedIn = AWSMobileClient.default().isSignedIn
            if let userState = userState {
                print("UserState: \(userState.rawValue)")
            } else if let error = error {
                print("error: \(error.localizedDescription)")

        if (self.userData.isSignedIn) {
            print("Loading data")

        return true

    func applicationWillTerminate(_ application: UIApplication) {
        // Called when the application is about to terminate. Save data if appropriate. See also applicationDidEnterBackground:.

    // MARK: UISceneSession Lifecycle
    func application(_ application: UIApplication, configurationForConnecting connectingSceneSession: UISceneSession, options: UIScene.ConnectionOptions) -> UISceneConfiguration {
        // Called when a new scene session is being created.
        // Use this method to select a configuration to create the new scene with.
        return UISceneConfiguration(name: "Default Configuration", sessionRole: connectingSceneSession.role)

    func application(_ application: UIApplication, didDiscardSceneSessions sceneSessions: Set<UISceneSession>) {
        // Called when the user discards a scene session.
        // If any sessions were discarded while the application was not running, this will be called shortly after application:didFinishLaunchingWithOptions.
        // Use this method to release any resources that were specific to the discarded scenes, as they will not return.
    // MARK: AWSMobileClient - Authentication
    public func authenticateWithDropinUI(navigationController : UINavigationController) {
        // Option to launch sign in directly
        let signinUIOptions = SignInUIOptions(canCancel: false)

        AWSMobileClient.default().showSignIn(navigationController: navigationController, signInUIOptions: signinUIOptions, { (signInState, error) in
            if let signInState = signInState {
                print("Sign in flow completed: \(signInState)")
            } else if let error = error {
                print("error logging in: \(error.localizedDescription)")

    public func authenticateWithHostedUI(navigationController : UINavigationController) {
        // Optionally override the scopes based on the usecase.
        let hostedUIOptions = HostedUIOptions(scopes: ["openid", "email", "profile", "aws.cognito.signin.user.admin"])

        // Present the Hosted UI sign in.
        AWSMobileClient.default().showSignIn(navigationController: navigationController, hostedUIOptions: hostedUIOptions) { (userState, error) in
            if let error = error as? AWSMobileClientError {
            if let userState = userState {
                print("Status: \(userState.rawValue)")

    public func signOut() {
    // MARK: AWSAppSync
    func appSyncInit() {
        do {
            // You can choose the directory in which AppSync stores its persistent cache databases
            let cacheConfiguration = try AWSAppSyncCacheConfiguration()

            // AppSync configuration & client initialization
            let appSyncServiceConfig = try AWSAppSyncServiceConfig()
            let appSyncConfig = try AWSAppSyncClientConfiguration(appSyncServiceConfig: appSyncServiceConfig,
                                                                  userPoolsAuthProvider: AWSMobileClient.default() as AWSCognitoUserPoolsAuthProvider,
                                                                  cacheConfiguration: cacheConfiguration)
            self.appSyncClient = try AWSAppSyncClient(appSyncConfig: appSyncConfig)
            print("Initialized appsync client.")
        } catch {
            print("Error initializing appsync client. \(error)")
    func queryLandmarks() {
        print("Query landmarks")
        self.appSyncClient?.fetch(query: ListLandmarksQuery(limit:100), cachePolicy: .fetchIgnoringCacheData) {(result, error) in
                if error != nil {
                    print(error?.localizedDescription ?? "")
                print("Landmarks query complete.")
                result?.data?.listLandmarks?.items!.forEach {
                    // convert the AppSync jsonObject (aka Dictionary<String, Any> to Data
                    // the code below assumes there is no casting / nil error
                    // TODO should add guard statement and handle errors
                    // https://nacho4d-nacho4d.blogspot.com/2016/05/dictionary-to-json-string-and-json.html
                    let jsonData = try! JSONSerialization.data(withJSONObject: $0?.jsonObject as Any, options: [])
                    // this allows to create a Landmark object using the Decodable protocol
                    let l : Landmark = try! JSONDecoder().decode(Landmark.self, from: jsonData)

// Make sure AWSMobileClient is a Cognito User Pool credentails providers
// this makes it easy to AWSMobileClient shared instance with AppSync Client
// read https://github.com/awslabs/aws-mobile-appsync-sdk-ios/issues/157 for details
extension AWSMobileClient: AWSCognitoUserPoolsAuthProviderAsync {
    public func getLatestAuthToken(_ callback: @escaping (String?, Error?) -> Void) {
        getTokens { (tokens, error) in
            if error != nil {
                callback(nil, error)
            } else {
                callback(tokens?.idToken?.tokenString, nil)

What we did change ?

  • import AWSAppSync framework and define a private reference to it.

  • initialize the AWSAppSyncClient client in the function func appSyncInit(). Notice that to make things easier, we extends AWSMobileClient to implement the AWSCognitoUserPoolsAuthProviderAsync protocol. This protocol allows to obtain Cognito tokens for the currently authenticated user. We pass the AWSMobileClient to the AWSAppSyncClient through its configuration object (AWSAppSyncClientConfiguration).

  • we added func queryLandmarks() to call the API. This function uses the generated code to pass arguments to the AppSync client. self.appSyncClient?.fetch() is asynchronous and returns immediately. We pass a callback inline function (result, error) in ... to be notified when the data are available. When data are available, the code transforms the JSON obect received in Landmark object (as defined in Landmarks/Models/Landmark.swift). Newly created objects are added to the array of Landmarks in UserData with this line of code self.userData.landmarks.append(l).

  • finally, we added code to query the API and to populate the Landmrk list (self.queryLandmarks()) at two places. First in the Authentication Listener Hub, when the app receives the .signedIn event, second in AWSMobileClient.default().initialize to ensure the application lods the list at startup, when the user is already authenticated.

The list of all changes we made to the code is visible in this commit.

Launch the app

Build and launch the application to verify everything is working as expected. Click the build icon or press ⌘R. build

After a few seconds, you should see the application running in the iOS simulator. run

If you did not sign out last time you started the application, you are still signed in. This is expected as the AWSMobileClient library stores the token locally and automatically refresh the token when it expires.

At this stage, we have hybrid data sources. The Landmark list is loaded from the GraphQL API, but the images are still loaded from the local bundle. In the next section, we are going to move the images to Amazon S3.