Fix "FirebaseApp is not initialized in this process"

App.kt

class App : Application() {
    var mainProcess = false
    var metricaProcess = false
  
    override fun onCreate() {
        val processName = ProcessUtil.getProcessName(this)
        mainProcess = processName==packageName
        metricaProcess = processName.contains(":AppMetrica") || processName.contains(":Metrica")

        if (!metricaProcess) { // you do not need to initialise anything manually inside the Metrica process
            if (!mainProcess) {
                // if you created the service yourself in a separate process (via android:process=":Something"), you should manually initialise Firebase in that process.
                FirebaseApp.initializeApp(this)
            }
            
             // put old onCreate code here, e.g:
             // FirebaseCrashlytics.getInstance().setUserId("someId")
             // if (mainProcess) MobileAds.initialize(this) { } // you probably don't want ads in the background process
             // ...
             
        }
        super.onCreate()
    }
}

ProcessUtil.java

public class ProcessUtil {
  //code from androidx.work.impl.utils
    public static String getProcessName(@NonNull Context context) {
        if (SDK_INT >= 28) {
            return Application.getProcessName();
        }

        // Try using ActivityThread to determine the current process name.
        try {
            @SuppressLint("PrivateApi") Class<?> activityThread = Class.forName(
                    "android.app.ActivityThread",
                    false,
                    ProcessUtils.class.getClassLoader());
            final Object packageName;
            Method currentProcessName = activityThread.getDeclaredMethod("currentProcessName");
            currentProcessName.setAccessible(true);
            packageName = currentProcessName.invoke(null);
            if (packageName instanceof String) {
                return (String) packageName;
            }
        } catch (Throwable exception) {
        }

        // Fallback to the most expensive way
        int pid = Process.myPid();
        ActivityManager am =
                (ActivityManager) context.getSystemService(ACTIVITY_SERVICE);

        if (am != null) {
            List<ActivityManager.RunningAppProcessInfo> processes = am.getRunningAppProcesses();
            if (processes != null && !processes.isEmpty()) {
                for (ActivityManager.RunningAppProcessInfo process : processes) {
                    if (process.pid == pid) {
                        return process.processName;
                    }
                }
            }
        }

        return null;
    }

}