In new Firebase, how to use multiple config file in xcode?

Better approach if you have single target is to just name your configs appropriately and load them as below. Seems to work fine for UAT environment example : Swift 3.0

    var fireBaseConfigFile = Bundle.main.path(forResource: "GoogleService-Info-PROD", ofType: "plist")
   #if UAT
       fireBaseConfigFile = Bundle.main.path(forResource: "GoogleService-Info-UAT", ofType: "plist")
   #endif

   guard let firOptions = FIROptions(contentsOfFile: fireBaseConfigFile) else {
       assert(false, "Failed to load Firebase config file")
       return
   }

   FIRApp.configure(with: firOptions)

Update: see Firebase official documentation https://firebase.google.com/docs/projects/multiprojects

Updated with an easier solution:

1. keep the same names for both GoogleService-Info.plist
2. put one GoogleService-Info.plist inside a subfolder, say "staging"
3. add references to both files in Xcode while linking them to corresponding targets
4. just use FIRApp.configure() in your AppDelegate, done

---

My first attempt that didn't solve the issue:

I renamed the second GoogleService-Info.json to something else and used following code to configure Firebase from AppDelegate.

// Swift code
#if STAGING
    let firebasePlistFileName = "GoogleService-Staging-Info"
#else
    let firebasePlistFileName = "GoogleService-Info"
#endif
let firbaseOptions = FIROptions(contentsOfFile: NSBundle.mainBundle().pathForResource(firebasePlistFileName, ofType: "plist"))
FIRApp.configureWithOptions(firbaseOptions)

If I run the Staging target, I will receive Firebase's complaint about 'Could not locate configuration file: 'GoogleService-Info.plist'.'. But then it says '<FIRAnalytics/INFO> Firebase Analytics v.3300000 started'.

As I checked on the Firebase dashboard, both production and staging apps have incoming user events being logged.

The above-mentioned configureWithOptions method is not documented in Firebase documentation, I figured it out by checking its source code. I'm not sure about what could be the downside of calling this. I would love to hear other approaches.

I've implemented something similar, as I've had two schemes for a single target that have different bundle identifiers. In my examples below, I have two different schemes, one for UAT and one for PROD.

Create the two GoogleService-Info.json files, and put them into your project directory (not Xcode project) in different folders, e.g.

ROOT/config/UAT/GoogleService-Info.json
ROOT/config/PROD/GoogleService-Info.json

Then add the files to your Xcode project like so:

Now you need to add a Run Script in your Build Phases. This will need to be added before the Compile Sources stage:

This Run Script takes the appropriately located json file and duplicates it into the build app directory, meaning Firebase/Google will identify it identically to how it would identify the file in a single identifier setup.

isUAT=`expr "$GCC_PREPROCESSOR_DEFINITIONS" : ".*UAT=\([0-9]*\)"`

RESOURCE_PATH=${SRCROOT}/${PRODUCT_NAME}/config/PROD

if [ $isUAT = 1 ]; then
    RESOURCE_PATH=${SRCROOT}/${PRODUCT_NAME}/config/UAT
fi

BUILD_APP_DIR=${BUILT_PRODUCTS_DIR}/${PRODUCT_NAME}.app

echo "Copying all files under ${RESOURCE_PATH} to ${BUILD_APP_DIR}"
cp -v "${RESOURCE_PATH}/"* "${BUILD_APP_DIR}/"

I would estimate you can use this same logic for Google Analytics as well, which uses a similar json config file setup.