Flutter android app crashes after adding Firebase library

Question

After adding Firebase Authentication library in flutter app, the app fails to compile and crashes with the error below

Launching lib/main.dart on TECNO LA7 in debug mode...
Initializing gradle...
Resolving dependencies...
Running Gradle task 'assembleDebug'...
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:8: error: package android.support.annotation does not exist
import android.support.annotation.NonNull;
                                 ^
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:534: error: cannot find symbol
    public void onComplete(@NonNull Task<AuthResult> task) {
                            ^
  symbol:   class NonNull
  location: class FirebaseAuthPlugin.SignInCompleteListener
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:554: error: cannot find symbol
    public void onComplete(@NonNull Task<Void> task) {
                            ^
  symbol:   class NonNull
  location: class FirebaseAuthPlugin.TaskVoidCompleteListener
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:572: error: cannot find symbol
    public void onComplete(@NonNull Task<ProviderQueryResult> task) {
                            ^
  symbol:   class NonNull
  location: class FirebaseAuthPlugin.ProvidersCompleteListener
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:168: error: cannot find symbol
                      public void onComplete(@NonNull Task<AuthResult> task) {
                                              ^
  symbol: class NonNull
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:263: error: cannot find symbol
          public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                                          ^
  symbol: class NonNull
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:416: error: cannot find symbol
              public void onComplete(@NonNull Task<GetTokenResult> task) {
                                      ^
  symbol: class NonNull
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:445: error: cannot find symbol
              public void onComplete(@NonNull Task<Void> task) {
                                      ^
  symbol: class NonNull
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:467: error: cannot find symbol
              public void onComplete(@NonNull Task<Void> task) {
                                      ^
  symbol: class NonNull
/Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java:483: error: cannot find symbol
          public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                                          ^
  symbol: class NonNull
Note: /Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java uses or overrides a deprecated API.
Note: Recompile with -Xlint:deprecation for details.
Note: /Users/mac/Downloads/flutter/.pub-cache/hosted/pub.dartlang.org/firebase_auth-0.5.20/android/src/main/java/io/flutter/plugins/firebaseauth/FirebaseAuthPlugin.java uses unchecked or unsafe operations.
Note: Recompile with -Xlint:unchecked for details.
10 errors

FAILURE: Build failed with an exception.

* What went wrong:
Execution failed for task ':firebase_auth:compileDebugJavaWithJavac'.
> Compilation failed; see the compiler error output for details.

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

BUILD FAILED in 0s
*******************************************************************************************
The Gradle failure may have been because of AndroidX incompatibilities in this Flutter app.
*******************************************************************************************
Finished with error: Gradle task assembleDebug failed with exit code 1

Answer 1

The problem is Firebase plugin uses AndroidX. You have to edit your gradle.properties file and add this two lines:

android.useAndroidX=true
android.enableJetifier=true

Flutter clean might be needed then too.