Freelance iOS Developer

The Data4Life app helps users manage their health, gain new knowledge, and contribute to research.

The biggest challenge in this project was to change the app's UI from UIKit to SwiftUI during ongoing development and change the overall architecture from VIPER to Composable Architecture. This was achieved by modularizing the app into over 50 Swift packages and then gradually transforming them.

In addition to the architecture and development part, the job involved coaching the staff in Composable Architecture and SwiftUI by means of pair programming and in-depth sessions.

Features:

• Keep track of symptoms
• Participate in studies
• Store medical documents digitally
• Knowledge base

Technologies used:

• UIKit
• SwiftUI
• Combine
• VIPER
• Composable Architecture
• Unit tests
• Fastlane
• SnapKit
• Swift Package Manager
• Sentry

12grapes GmbH is the company behind the app Bunch, an AI coach that makes it easy to learn and grow your leadership skills with bite-sized daily tips.

I joined Bunch in August 2020 to help develop new features and reduce the technical depth to make the app more performant, maintainable, and testable at the same time. To achieve this, I've built a backend with a REST API and outsourced some of the app's business logic. Furthermore, I introduced Functional Reactive Programming in an MVVM setup.

Features:

• Multi-step onboarding
• Search
• Explore Content
• Gamification
• User profiles
• Read or listen to tips
• Social sharing
• Calendar integration

Technologies used:

• SwiftUI
• Combine
• MVVM
• In-App Purchase Subscriptions
• Fastlane
• Travis CI
• Unit tests
• Firebase Firestore
• Firebase Cloud Functions
• Firebase Authentication
• Firebase Cloud Storage
• Google App Engine

In December 2019 I joined the app team of Sparkasse's agency S-Markt & Mehrwert GmbH to support them on one of their projects, a white label customer loyalty app they're offering to their partners, one of which is Hamburger Sparkasse's app HaspaJoker.

Through the app, customers get special offers and discounts from local partners, can book travel/concert tickets and benefit from a variety of other perks and services. The agile scrum team consisted of 5 iOS, 4 Android as well as 4 backend developers and was working predominantly remotely. Some of the work I did included refactoring and consolidating the codebase to be testable, introducing Screenshot tests, automating tasks, and implementing new features.

Technologies used:

• XCode
• RxSwift
• Fastlane
• Alamofire
• SwiftLint
• SnapKit
• MVVM
• REST-Api
• AppCenter
• SwiftGen
• Coordinator
• Snapshot tests
• Unit tests
• GIT
• Scrum

Spielworks hired me to kick-start their product "Wombat" for iOS. For this greenfield project, I did both the architecture and the implementation of the beta version and later hired another developer who eventually took the project over.

The app is the first EOS wallet built for everyday use and simplifies the creation of EOS accounts through a three-step onboarding process. It automatically encrypts and stores the private key in the cloud and makes sending/receiving EOS tokens a breeze. One of the core features of the app is the DAPP Browser that acts as a proxy between DAPP and the EOS account and provides a streamlined user-interface to sign transactions.

Features:

• Login
• EOS account creation
• Send/Receive EOS tokens
• Sign transactions
• SDK for third-party apps
• Manage EOS keys
• Unlock private key
• Prime subscription
• EOS resources overview

Technologies used:

• In-App-Purchases
• EOS Blockchain
• AES Cryptography
• Sign in with Apple, Facebook, Twitter and Email
• Firebase
• Crashlytics
• RxSwift
• MVVM
• Google Drive
• Dropbox
• Unit tests

After having helped out Vantik as a freelancer end of 2017, I joined full-time in 2018 to build up the entire frontend stack and team. Vantik is an investment-based retirement savings product (private pension). Since Vantik is a banking product, highest priority in all layers of the stack was security and compliance with the German federal financial supervisory authority (BaFin).

Stack:

• Customer web app BaFin compliant multi-step user registration, deposit & withdraw money, payment history, multi-factor authentication, change linked bank account, tax exemption settings, account settings, account balance, customer login, reset & change password

• Admin web app User management, payment management, voucher codes

• Visitor website Static website generator fed by a headless CMS (Prismic) and hosted on AWS S3

• App (iOS) Customer login, account balance, deposit & withdraw, account settings

Technologies used: Customer web app:

• Vue.js
• Bootstrap
• Node.js
• Webpack
• AWS Cognito
• AWS Cloudformation
• AWS S3
• AWS Lambda

Admin web app:

• Vue.js
• Bootstrap
• AWS S3
• AWS Cloudformation
• AWS CloudFront
• AWS Cognito
• Webpack

Visitor website:

• Node.js
• Express.js
• Prismic.io (Headless CMS)
• Pug

App (iOS):

• Swift
• UIKit
• Alamofire
• RxSwift
• MVVM
• Reactive programming

Together with another app developer I've built the native iOS swift (universal - iPhone & iPad) app for Wine in Black, a wine e-commerce company. Due to the fact that Wine in Black is a curated shop with a limited, constantly changing assortment, the app stores all active products on the device and syncs with the server on startup so that all interactions with products such as browse, search or filter are instant and do not require a network connection.

Besides working on the iOS app, another part of the job was building a new REST API. This was necessary because the existing shop system was being replaced during the project.

Features:

• Push notifications
• Campaigns
• Product detail page
• Cart
• Checkout
• Order history
• Profile
• Filters & search
• Custom transitions
• Store country switching
• User registration & login

Technologies used: App:

• Swift
• UIKit
• iAd
• Core Image
• Fabric
• Fastlane
• OneSignal
• Crashlytics
• Analytics

Backend:

• PHP
• Spryker Commerce OS
• MySQL
• Integration tests

During studies, I was working on the media library app for Deutschlandradio Wissen.

Features:

• Login
• Registration
• Category overview
• Article detail page
• Audio streaming
• Starring favorite articles
• Push notifications

Technologies used:

• Objective-C
• UIKit
• MVC
• Core Animation
• Core Image
• AVFoundation
• AFNetworking