问Firebase Android onAuthStateChanged()在signInWithEmailAndPassword()之后触发两次

EN

public class SignInActivity extends BaseActivity implements
        View.OnClickListener,
        GoogleApiClient.OnConnectionFailedListener{

    private static final String PREF_KEY_USER_EMAIL = "User_Email";
    private static final int RC_SIGN_IN = 1111;

    private FirebaseAuth firebaseAuth;
    private FirebaseAuth.AuthStateListener authStateListener;
    private DatabaseReference firebaseDbReference;

    private TextView fieldEmail;
    private TextView fieldPassword;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_sign_in);
        getSupportActionBar().hide();

        firebaseAuth = FirebaseAuth.getInstance();
        firebaseDbReference = FirebaseDatabase.getInstance().getReference();
        fieldEmail = (TextView) findViewById(R.id.field_email);
        fieldPassword = (TextView) findViewById(R.id.field_password);

        String userSavedEmail = getPreferences(MODE_PRIVATE).getString(PREF_KEY_USER_EMAIL, "");
        if(userSavedEmail != null) {
            fieldEmail.setText(userSavedEmail);
            fieldPassword.requestFocus();
        }

        TextView linkForgotPassword;
        Button buttonLogin;

        linkForgotPassword = (TextView) findViewById(R.id.link_forgotPassword);
        buttonLogin = (Button) findViewById(R.id.button_Login);
        buttonSignUp = (Button) findViewById(R.id.button_signUp);

        if (linkForgotPassword != null) {
            linkForgotPassword.setOnClickListener(this);
        }
        if (buttonLogin != null) {
            buttonLogin.setOnClickListener(this);
        }
        if (buttonSignUp != null) {
            buttonSignUp.setOnClickListener(this);
        }

        authStateListener = new FirebaseAuth.AuthStateListener() {
            @Override
            public void onAuthStateChanged(@NonNull FirebaseAuth firebaseAuth) {
                if(firebaseAuth.getCurrentUser() != null) {
                    onAuthSuccess(firebaseAuth.getCurrentUser());
                }
            }
        };
    }

    @Override
    protected void onStart() {
        super.onStart();
        firebaseAuth.addAuthStateListener(authStateListener);
    }

    @Override
    protected void onStop() {
        super.onStop();
        if (authStateListener != null) {
            firebaseAuth.removeAuthStateListener(authStateListener);
        }
    }

    @Override
    public void onClick(View v) {
        switch (v.getId()){
            case R.id.link_forgotPassword:
                forgotPassword();
                break;
            case R.id.button_Login:
                emailLogin();
                break;
            case R.id.button_signUp:
                emailSignUp();
                break;
        }
    }

    @Override
    public void onConnectionFailed(@NonNull ConnectionResult connectionResult) {
        Toast.makeText(this, "Google Play Services error.", Toast.LENGTH_SHORT).show();
    }

    private void forgotPassword(){
        FirebaseAuth auth = FirebaseAuth.getInstance();
        String emailAddress = fieldEmail.getText().toString();

        if(TextUtils.isEmpty(emailAddress)){
            Toast.makeText(SignInActivity.this, R.string.msg_EnterEmail,
                    Toast.LENGTH_SHORT).show();
        }
        else {
            showProgressDialog();
            auth.sendPasswordResetEmail(emailAddress)
                    .addOnCompleteListener(new OnCompleteListener<Void>() {
                        @Override
                        public void onComplete(@NonNull Task<Void> task) {
                            hideProgressDialog();
                            if (task.isSuccessful()) {
                                Toast.makeText(SignInActivity.this, R.string.msg_ResetPasswordEmailSent,
                                        Toast.LENGTH_LONG).show();
                            }
                        }
                    });
        }
    }

    private void emailLogin(){
        if (!validateForm()) {
            return;
        }

        showProgressDialog();
        String email = fieldEmail.getText().toString();
        String password = fieldPassword.getText().toString();

        firebaseAuth.signInWithEmailAndPassword(email, password)
                .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        hideProgressDialog();

                        if (!task.isSuccessful()) {
                            Toast.makeText(SignInActivity.this, R.string.msg_EmailLoginFailed,
                                    Toast.LENGTH_SHORT).show();
                        }
                        else {
                            // Save the email
                            getPreferences(MODE_PRIVATE).edit()
                                    .putString(PREF_KEY_USER_EMAIL, fieldEmail.getText().toString())
                                    .apply();
                        }
                    }
                });
    }

    private void emailSignUp(){
        if (!validateForm()) {
            return;
        }

        showProgressDialog();
        String email = fieldEmail.getText().toString();
        String password = fieldPassword.getText().toString();

        firebaseAuth.createUserWithEmailAndPassword(email, password)
                .addOnCompleteListener(new OnCompleteListener<AuthResult>() {
                    @Override
                    public void onComplete(@NonNull Task<AuthResult> task) {
                        hideProgressDialog();

                        if (task.isSuccessful()) {
                            FirebaseUser user = task.getResult().getUser();
                            String displayName = displayNameFromEmail(user.getEmail());

                            // Update profile display name.
                            UserProfileChangeRequest profileUpdates = new UserProfileChangeRequest.Builder()
                                    .setDisplayName("Jane Q. User")
                                    .build();
                            user.updateProfile(profileUpdates);
                        } else {
                            Toast.makeText(SignInActivity.this, R.string.msg_EmailSignUpFailed,
                                    Toast.LENGTH_SHORT).show();
                        }
                    }
                });
    }

    private void onAuthSuccess(FirebaseUser user) {
        // Write new user
        writeNewUser(user.getUid(),
                user.getDisplayName(),
                user.getEmail(),
                user.getPhotoUrl());

        // Go to MainActivity
        startActivity(new Intent(this.getApplicationContext(), MainActivity.class));
        finish();
    }

    private void writeNewUser(String userId, String displayName, String email, android.net.Uri photoUrl) {
        User user = new User(displayName, email);

        if(photoUrl != null){
            user.setPhotoUrl(photoUrl.toString());
        }

        firebaseDbReference.child("users").child(userId).setValue(user);
    }

    private String displayNameFromEmail(String email) {
        if (email.contains("@")) {
            return email.split("@")[0];
        } else {
            return email;
        }
    }

    private boolean validateForm() {
        boolean result = true;
        if (TextUtils.isEmpty(fieldEmail.getText().toString())) {
            fieldEmail.setError("Required");
            result = false;
        } else {
            fieldEmail.setError(null);
        }

        if (TextUtils.isEmpty(fieldPassword.getText().toString())) {
            fieldPassword.setError("Required");
            result = false;
        } else {
            fieldPassword.setError(null);
        }

        return result;
    }
}