Storing API Keys and Other Constants in Swift 3

Introduction

After your app is on the App Store, you’ll have at least two states of your app to maintain: the app as it is on the App Store, and the app that you actively add features to in development.

If you have a server running in the backend, you’ll definitely have a server for production and a server for active development. On the iOS development side, we need some way of organizing our code base to prevent crashing the production version of the app.

A Constants file or the info.plist file is commonly used to store variables which not only contain sensitive data, but might also change depending on the state of your app—like server URLs and API keys.

This is a guide to setting up different configurations of your app through schemes for different states of the app: Debug, Development, and Release — and specifying our configurations in the Project Settings.

How To Add .xcconfig Files To Your XCode Project

You can download the starter project here if you aren’t using Cocoapods, and here if you are.

1. Create a new folder in your XCode project — I called mine Config. I’m adding three .xcconfig files: Development, Debug, and Release.

2. Add your configuration files to your project settings. You’ll most likely have to create an extra Configuration for Development.

If you’re not using Cocoapods, you can skip to #3. If you are using Cocopods, you’ll have to delete the .xcworkspace file, the Podfile.lock, and the Pods/ directory. Do not delete the Podfile.

Then, go to your terminal. Make sure that you’re in the project directory and run pod install.

Now, open the newly generated .xcworkspace file and add the .xcconfig path for Cocoapods in your own .xcconfig file.

3. Add new schemes to your project and make sure your target is your XCode project name. Set up your scheme to correspond to your configuration.

4. Now you can set variables in your config files and access them via your info.plist file.

Warnings and Common Pitfalls

• Beware of putting a string as a value for a key within a .xcconfig file — it automatically stringifies any value.
• In these examples, I pushed my .xcconfig files to my repo so you can download and run the project. In a real working environment, you should put these files in your .gitignore — and then have a private repository to keep up with updates in the config files.

You can find the working code here if you weren’t using Cocoapods, and here if you were. Please let me know if you have any questions!

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