When running the sample after creating google-service.json, the app crashes when trying to get database reference in SignInActivity
mDatabase = FirebaseDatabase.getInstance().getReference();
Crash log
05-21 09:27:27.644 488-488/com.google.firebase.quickstart.database D/AndroidRuntime: Shutting down VM
05-21 09:27:27.644 488-488/com.google.firebase.quickstart.database E/AndroidRuntime: FATAL EXCEPTION: main
Process: com.google.firebase.quickstart.database, PID: 488
java.lang.RuntimeException: Unable to start activity ComponentInfo{com.google.firebase.quickstart.database/com.google.firebase.quickstart.database.SignInActivity}: com.google.firebase.database.DatabaseException: Failed to get
FirebaseDatabase instance: FirebaseApp object has no DatabaseURL in its FirebaseOptions object.
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2325)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
Caused by: com.google.firebase.database.DatabaseException: Failed to get FirebaseDatabase instance: FirebaseApp object has no DatabaseURL in its FirebaseOptions object.
at com.google.firebase.database.FirebaseDatabase.getInstance(Unknown Source)
at com.google.firebase.database.FirebaseDatabase.getInstance(Unknown Source)
at com.google.firebase.quickstart.database.SignInActivity.onCreate(SignInActivity.java:39)
at android.app.Activity.performCreate(Activity.java:5990)
at android.app.Instrumentation.callActivityOnCreate(Instrumentation.java:1106)
at android.app.ActivityThread.performLaunchActivity(ActivityThread.java:2278)
at android.app.ActivityThread.handleLaunchActivity(ActivityThread.java:2387)
at android.app.ActivityThread.access$800(ActivityThread.java:151)
at android.app.ActivityThread$H.handleMessage(ActivityThread.java:1303)
at android.os.Handler.dispatchMessage(Handler.java:102)
at android.os.Looper.loop(Looper.java:135)
at android.app.ActivityThread.main(ActivityThread.java:5254)
at java.lang.reflect.Method.invoke(Native Method)
at java.lang.reflect.Method.invoke(Method.java:372)
at com.android.internal.os.ZygoteInit$MethodAndArgsCaller.run(ZygoteInit.java:903)
at com.android.internal.os.ZygoteInit.main(ZygoteInit.java:698)
How to fix this issue ?
Vihaan Verma
Download google-services.json from Project Settings in the Firebase console. My mistake was downloading it from https://developers.google.com/mobile/add.
colour Blue
mFirebaseDatabaseReference = database.getInstance().getReference("root-element in firebase");
When you call getReference you need to provide a URL. If your project is bound already in Firebase with the database you have created, use the root element of the data in Firebase as the parameter to getReference().
来源：https://stackoverflow.com/questions/37363791/firebase-database-getinstance-crashes-app