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Firebase Authentication (email and password) How to check if user still exists?

I'm using Firebase Authentication in my app (email and password auth).
In the onStart() method of my Login activity I retrieve the current user using:
FirebaseUser currentUser = mAuth.getCurrentUser();
The problem comes when the user is deleted from the database, the mAuth.getCurrentUser() method still retrieves the user and allows authentication.
How can I check if the user still exists?
Thx!

Try using something like this:
DatabaseReference ref = FirebaseDatabase.getInstance().getReference();
ref.child("users").child("email").addListenerForSingleValueEvent(new
ValueEventListener() {
#Override
public void onDataChange(DataSnapshot dataSnapshot) {
if(dataSnapshot.exists()){
// used "email" already exists and is not deleted
} else {
// User does not exist. Add here your logic if the user doesn't exist
}
}
#Override
public void onCancelled(DatabaseError databaseError) {
}
});
Or check some of the following SO questions and answers:
Firebase authentication for checking if the user exists in the database or not
Firebase Auth - with Email and Password - Check user already registered

You can use getInstance. This worked for me fine. You don't get an instance with it.
private boolean isSignedIn() {
return FirebaseAuth.getInstance().getCurrentUser() != null;
}

Delete the userdata and make the currentuser null:
Follow the below code.
final FirebaseUser user = FirebaseAuth.getInstance().getCurrentUser();
user.delete()
.addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
if (task.isSuccessful()) {
Log.d(TAG, "User account deleted.");
//Remove the information f the user from database.
}
}
});

The code below works great on android to confirm if the Firebase Auth user still exists (has not been deleted or disabled) and has valid credentials.
Deleting the Auth user from the firebase console does not revoke auth tokens on devices the user is currently logged in as the token is cached locally. Using reload() forces a check with the firebase auth server.
currentUser.reload().addOnCompleteListener(new OnCompleteListener<Void>() {
#Override
public void onComplete(#NonNull Task<Void> task) {
if(task.isSuccessful()){
//User still exists and credentials are valid
}else {
//User has been disabled, deleted or login credentials are no longer valid,
//so send them to Login screen
}
}
});

Firebase documentation: where is the documentation for FirebaseAuth?

I am at https://firebase.google.com/docs/auth/android/start/ and I see this code snippets:
private FirebaseAuth mAuth;
mAuth = FirebaseAuth.getInstance();
mAuth.createUserWithEmailAndPassword(email, password)
.addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
if (task.isSuccessful()) {
// Sign in success, update UI with the signed-in user's information
Log.d(TAG, "createUserWithEmail:success");
FirebaseUser user = mAuth.getCurrentUser();
updateUI(user);
} else {
// If sign in fails, display a message to the user.
Log.w(TAG, "createUserWithEmail:failure", task.getException());
Toast.makeText(EmailPasswordActivity.this, "Authentication failed.",
Toast.LENGTH_SHORT).show();
updateUI(null);
}
// ...
}
});
I believe that the "FirebaseAuth" class is not part of the FirebaseUI library. I believe it is a part of the firebase SDK.
So I go to the reference for the firebase SDK (https://firebase.google.com/docs/reference/android/com/google/firebase/package-summary). But I cannot find this class anywhere, or the method .createUserWithEmailAndPassword(email, password).
Can someone point me to the documentation for FirebaseAuth? I guess the answer I am looking for would be a URL, along with a conceptual explanation of how this code is organized.

Here you go: https://developers.google.com/android/reference/com/google/firebase/auth/FirebaseAuth
I don't see where else you would rather find this.

Firebase email verification WITHOUT creating and account

I'm creating an Android application that will deliver notifications.
Users can opt-in with a phone number or an email account.
I just need to verify the email the user entered, I don't want to create a Firebase account
Firebase has a FirebaseUser#sendEmailVerification() but that will require to create an account.
In other words, I just want the email verification to be the same as the Phone verification, where Firebase will just send you a code or verification link.
Is there a way to leverage Firebase email verification without creating an account?

For anyone trying to accomplish the same, here's how I was able to do it.
Go to Fibrebase console and enable Email/Password and Anonymous sign-in methods on the Authentication screen
Firebase Authentication screen
Then in you code, create an Anonymous user (this is what does the trick, because now you have a valid user to verify against), change the email, and then send a verification. After that, reload the Firebase user and check isEmailVerified()
mAuth = FirebaseAuth.getInstance();
mAuth.signInAnonymously()
.addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
if (task.isSuccessful()) {
Log.d(TAG, "signInAnonymously:success");
if (mAuth.getCurrentUser().isEmailVerified() == false) {
mAuth.getCurrentUser().updateEmail("<MAIL YOU WANTO TO VERIFY HERE>");
mAuth.getCurrentUser().sendEmailVerification();
Log.e(TAG, "mail sent.....................................");
}
//updateUI(user);
} else {
// If sign in fails, display a message to the user.
Log.w(TAG, "signInAnonymously:failure", task.getException());
Toast.makeText(getApplicationContext(), "Authentication failed.",
Toast.LENGTH_SHORT).show();
}
}
});
Here's the reloading part:
mAuth.getCurrentUser().reload()
.addOnSuccessListener(new OnSuccessListener<Void>() {
#Override
public void onSuccess(Void aVoid) {
Log.e(TAG,( mAuth.getCurrentUser().isEmailVerified() ? "VERIFIED" : "Not verified"));
}
});

Both phone number verification and email verification are tied to a Firebase Authentication account. There is no way to use them with such an account, since the result of a verification is that a the relevant property (email_verified or phone_number) in the user account gets updated.

How to handle FirebaseAuthUserCollisionException

I started getting a FirebaseAuthUserCollisionException exception when I try to sign in with Facebook in my Android application.
com.google.firebase.auth.FirebaseAuthUserCollisionException: An
account already exists with the same email address but different
sign-in credentials. Sign in using a provider associated with this
email address.
I am using Firebase to handle the registration and Facebook to deliver a "one-click" login method, using a com.facebook.login.widget.LoginButton view as a trigger.
These sign-in method was already working. I was able to register a account with Facebook, and use the same method to log-in this account. But now have start to throwing this exception.
Here is the code where I register a account from Facebook and proceed with login:
private void handleFacebookAccessToken(AccessToken token) {
final ProgressDialog dialog = new ProgressDialog(this);
dialog.show(getString(R.string.dialog_wait));
firebaseAuth.signInWithCredential(FacebookAuthProvider.getCredential(token.getToken()))
.addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
#SuppressWarnings("ThrowableResultOfMethodCallIgnored")
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
if (task.isSuccessful()) {
dialog.close();
registerNewUserFromSocialLogin(firebaseAuth.getCurrentUser());
} else {
if(task.getException() instanceof FirebaseAuthUserCollisionException) {
//TODO: handle sign-in with different credentials
} else {
dialog.close();
LoginManager.getInstance().logOut();
Toast.makeText(LoginActivity.this,
R.string.error_login,
Toast.LENGTH_SHORT).show();
}
}
}
});
}
And my Gradle file with current use library:
compile 'com.google.firebase:firebase-auth:10.2.1'
compile 'com.facebook.android:facebook-android-sdk:[4,5)'
So my problem is: I don't know how to handle FirebaseAuthUserCollisionException exception.
None of the solutions in StackOverflow or Firebase Documentation help me. I am looking for a solution that is able to login the user although the duplicated credential, to stil deliver the "one-click" login method.

You will get that error when the user had previously signed in with the same email using a different provider. For example, the user signs in with email user#gmail.com using Google. The user then tries to sign in with the same email but using Facebook. The Firebase Auth backend will return that error (account exists with different credential). In that case, you should use the fetchProvidersForEmail to look up the existing providers associated with email user#gmail.com, in this case google.com. You signInWithCredential to the existing google account to prove ownership of that account, and then linkWithCredential the Facebook credential the user originally was trying to sign in with. This merges both accounts so in the future the user can sign in with either.
This happens when you use the single accounts per email. If you want to allow different accounts per email, you can switch to multiple accounts per email in the Firebase console.
Here is an example:
mAuth.signInWithCredential(authCredential)
.addOnCompleteListener(this, new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
// Account exists with different credential. Assume the developer wants to
// continue and link new credential to existing account.
if (!task.isSuccessful() &&
task.getException() instanceof FirebaseAuthUserCollisionException) {
FirebaseAuthUserCollisionException exception =
(FirebaseAuthUserCollisionException)task.getException();
if (exception.getErrorCode() ==
ERROR_ACCOUNT_EXISTS_WITH_DIFFERENT_CREDENTIAL) {
// Lookup existing account’s provider ID.
mAuth.fetchProvidersForEmail(existingAcctEmail)
.addOnCompleteListener(new OnCompleteListener<ProviderQueryResult> {
#Override
public void onComplete(#NonNull Task<ProviderQueryResult> task) {
if (task.isSuccessful()) {
if (task.getResult().getProviders().contains(
EmailAuthProvider.PROVIDER_ID)) {
// Password account already exists with the same email.
// Ask user to provide password associated with that account.
...
// Sign in with email and the provided password.
// If this was a Google account, call signInWithCredential instead.
mAuth.signInWithEmailAndPassword(existingAcctEmail, password)
addOnCompleteListener(new OnCompleteListener<AuthResult> {
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
if (task.isSuccessful()) {
// Link initial credential to existing account.
mAuth.getCurrentUser().linkWithCredential(authCredential);
}
}
});
}
}
}
});
}
}
});

There is no need for this, you can just allow multiple accounts merge under firebaase->authentication-> sign in method -> Advanced - > change (multiple accounts per email address.
Firebase will merge the same email address but will give you different user UID.
See sample below.
AuthCredential authCredential = FacebookAuthProvider.getCredential(token.getToken());
mAuth.signInWithCredential(authCredential)
.addOnCompleteListener(this, task -> {
if (task.isSuccessful()) {
// Sign in success, update UI with the signed-in user's information
Log.d(TAG, "signInWithCredential:success");
FirebaseUser user = mAuth.getCurrentUser();
LoginFacebookGoogleActivity.this.updateUI(user);
} else {
// If sign in fails, display a message to the user.
Log.w(TAG, "signInWithCredential:failure", task.getException());
if(task.getException() instanceof FirebaseAuthUserCollisionException){
FirebaseAuthUserCollisionException exception = (FirebaseAuthUserCollisionException) task.getException();
//log this bundle into the analytics to analyze which details you want to collect
}
Toast.makeText(LoginFacebookGoogleActivity.this, "Authentication failed " + task.getException(), Toast.LENGTH_SHORT).show();
LoginFacebookGoogleActivity.this.updateUI(null);
}
});

Android- How to upload image to Firebase under specific users

I am developing an app, and so far it's able to upload images, and register users.
However, these two functionalities run independent of each other. Ergo, I need to make it so that the images are saved under the user that uploads it. I am a novice Android programmer and just started learning about Firebase and could use the help.

In Registration process,
FirebaseAuth.getInstance()
.createUserWithEmailAndPassword(email, email)
.addOnCompleteListener(new OnCompleteListener<AuthResult>() {
#Override
public void onComplete(#NonNull Task<AuthResult> task) {
android.util.Log.e("Firebase", "performFirebaseRegistration:onComplete:" + task.isSuccessful());
// If sign in fails, display a message to the user. If sign in succeeds
// the auth state listener will be notified and logic to handle the
// signed in user can be handled in the listener.
if (!task.isSuccessful()) {
AlertUtils.showAlert(MainActivity.this, getString(R.string.sign_up), task.getException().getMessage());
} else {
FirebaseUser firebaseUser = task.getResult().getUser(); // here you will get userDetails
}
}
});
From firebaseUser you can get user id by firebaseUser.getUid().
Once you upload the message,sent to realtime firebase b the user id as below,
DatabaseReference database = FirebaseDatabase.getInstance().getReference();
database.child(ARG_USERS)
.child(firebaseUser.getUid())
.child("image")
.setValue(<you image download url>);