How to build an offline-first iPhone application

What do Google Drive, MS Office, Spotify, Evernote, and Google Maps have in common? They can work without the Internet. Although you won’t get to access all the features, they still are built to perform even in offline mode. The reason why businesses and app developers are incorporating offline functionalities in their applications is that they do not want users to abandon the app in situations where:

• There is no internet connection: in flights and metro tunnels
• There is a limited internet bandwidth: locations with poor network coverage
• You have occasional data access: like on Wifi-only devices

If you want your iOS applications to have offline functionalities or perform all the functionalities without the Internet, you are at the right place. In this post, you’ll learn everything you need to know about offline-first iOS app development and some strategies to build it successfully.

Table of contents

What makes an app offline-first?
How do offline-first iOS applications work?
Strategies for developing offline-first iOS applications?
* Clearly define offline cases
* Implement a data synchronization mechanism with background tasks
* Design UI/UX keeping offline users in mind
* Implement token-based authentication for enhanced security
Step-by-step guide to developing an offline-first iOS application
* STEP 1: Choosing the right database
* STEP 2: Offline Data Storage implementation
=> Set up CoreData
=> Implement data sync
* STEP 3: Conflict resolution
* STEP 4: Network handling and API design
* STEP 5: Error handling
* STEP 6: Testing
Bottom line

What makes an app offline-first?

To be able to be called as an offline-first, the application must be able to fulfill the following criteria:

• Able to perform most of the functions in offline mode
• Incorporate robust local data storage mechanism to allow users access to critical data without the internet
• Seamlessly synchronize data between the local device and the server
• Store data in the local cache and sync that data when the app gets reconnected to the internet

How do offline-first iOS applications work?

Unlike traditional iPhone applications that rely on a central server for data storage and retrieval, offline-first apps store a significant amount of data locally on the user’s device. This approach allows users to access essential information without requiring a constant internet connection, making the app more robust and reliable in various situations.

Here’s a breakdown of how offline-first iOS apps work:

Local data storage: Offline-first apps store a substantial amount of data on the user’s device, ranging from user preferences and settings to critical content that users may need even when offline. The local storage can include databases, files, or caches that enable the app to function independently of an internet connection.

Initial data synchronization: When the user first installs the app or launches it after an update, there is usually an initial synchronization process with the central server to fetch the latest data.

Offline access: Once the initial synchronization is complete, the app is capable of running offline, providing users with access to the locally stored data. Users can interact with the app, view saved content, and perform certain tasks without relying on real-time server communication.

Offline data modification: Users can create, edit, or delete data within the app even when offline. Any changes made are stored locally on the device and are later synchronized with the server when an internet connection is available.

Strategies for developing offline-first iOS applications?

1). Clearly define offline use cases

It helps in determining which aspects of your iOS app should operate offline and also in understanding your app’s essence, user expectations, and the situations where users might lack an internet connection. Let’s explore how you can pinpoint the offline functionalities of your application.

Understand user needs: Start by understanding the primary use cases and needs of your target users. Consider the typical scenarios in which users might want to access your app without an internet connection.

Consider critical content: Identify content that users might want to access in offline mode. This could include documents, media files, or other essential information.

Analyze usage patterns: User behavior and usage patterns can help you identify features frequently used or deemed critical by users. Prioritize making these features available offline to enhance overall user satisfaction.

2). Deploy a data synchronization mechanism with background tasks

When building an offline-first app, you must have a mechanism that can update the local data when the app comes back online. Here’s how you can do that

• Design a background task system to periodically check for internet connectivity.
• Incorporate logic to synchronize local data with the server when an internet connection is detected.
• Utilize iOS background task APIs to ensure synchronization occurs even when the app is in the background.

3). Design UI/UX keeping offline users in mind

Tailoring the UI to reflect the app’s offline capabilities, providing informative feedback, and guiding users to available features contribute to a positive user experience.

• Customize the UI to provide clear indications of the user’s offline status.
• Display well-defined error messages to inform users when certain features are unavailable offline.
• Incorporate intuitive navigation and interactions that guide users to available offline functionalities.

4). Implement token-based authentication for enhanced security

Storing encrypted tokens locally ensures a seamless login experience without compromising security. This strategy enhances both the usability and security of the app in offline scenarios.

• Deploy token-based authentication to allow users to log in and access the app offline securely.
• Store encrypted authentication tokens locally for persistent user sessions.
• Design a secure mechanism to refresh tokens and manage user authentication while offline.

Note: A critical consideration before taking up offline-first iOS app development is how to do it. For instance, a business owner may choose to hire mobile app developers from a third-party iPhone app development company. Or, they may choose to build an in-house team with this skillset. You must get this decision out of the way after performing necessary cost calculations, so that you can move on to building the solution.

Step-by-step guide to developing an offline-first iPhone application

STEP 1: Choosing the right database

When selecting the right database for offline-first iOS application development, it’s essential to consider factors like local storage capability, synchronization with a remote database, and compatibility with the iOS platform. Here are some options:

Core data:

• Apple’s native solution for data management.
• Offers robust features for data modeling, storage, and retrieval.
• Well-integrated with other Apple frameworks.

Realm:

• A lightweight, yet powerful, alternative to Core Data.
• Boasts excellent performance and a simple API.
• Supports automatic synchronization and offline access.

SQLite:

• A widely-used relational database with a strong community of users and developers.
• Ideal for complex data structures and relationships.
• Can be customized to support offline caching.

STEP 2: Offline data storage implementation

Set up CoreData

• Create a CoreData model for your app’s data.
• Apply CoreData stack initialization in your app.

Apply data sync

• Create functions to sync data between the local and remote databases
• Handle conflicts that may arise during synchronization

STEP 3: Conflict resolution

Conflict resolution is an integral aspect of offline-first iPhone app development, especially when the locally written data conflicts with the information stored in the network data source. Before synchronization can occur, it is imperative to address and resolve such conflicts.

Various strategies can be employed for conflict resolution, with the choice depending on the specific needs of the application. For IOS applications, Last Write Wins is the most commonly used approach. Here’s how it works.

Each piece of data is associated with a timestamp or version number to track changes.

When synchronization occurs, the app checks for conflicts by comparing the timestamps or version numbers of locally modified data with the corresponding data on the server. If a conflict is detected, the app prioritizes the version with the latest timestamp or version number, considering it as the most recent change.

STEP 4: Network handling and API design

Efficient network handling and well-designed APIs are pivotal for offline-first applications. Consider the following best practices:

Optimizing network requests

• Apply background fetching to update data when the app is in the background.
• Prioritize critical data to minimize bandwidth usage during synchronization.
• Leverage caching strategies to store frequently accessed data locally.

API design for offline support

• Enable endpoints that allow bulk data retrieval for offline usage.
• Deploy idempotent APIs to handle scenarios where the same request is made multiple times.
• Use optimistic updates to reflect changes in the UI immediately, syncing with the server in the background.

STEP 5: Error handling

You need to implement error-handling procedures to avoid interruptions during offline usage. This involves anticipating and managing potential issues that may arise during network requests, local data operations, or other critical processes.

Network error handling

• To tackle issues such as timeouts, connection issues, and server errors you need to incorporate robust error handling for network requests.
• Implement a retry mechanism for failed network requests to allow the app to automatically retry the operation when connectivity is restored.

Local data error handling

• Anticipate errors that may occur during local data operations, such as database failures or data corruption
• Use try-catch blocks or appropriate error-handling mechanisms when performing CRUD operations on local data.

Offline mode handling

• Design the UI to indicate the offline status and inform users about the limited functionality available without an internet connection.
• Queue and postpone non-critical operations until the app is online again.

STEP 6: Testing

Testing is a crucial aspect of developing an offline-first iOS application. It involves systematically evaluating different components and scenarios to ensure the app functions reliably and provides a seamless user experience. Implement the following testing to ensure your app is reliable, robust and running smoothly.

• Unit Testing
• Integration testing
• UI/UX testing
• Performance testing
• Usability testing

Bottom line

The journey of offline-first iOS app development is both challenging and rewarding. By prioritizing offline functionality, developers can create apps that not only meet but exceed user expectations. Using the strategies and implementation tips discussed in this article, iOS app developers can navigate the complexities of offline-first development and craft applications that thrive in a connected world.