必须将OnCompleteListener声明为抽象，或在OnCompleteListener中实现抽象方法“ onComplete（Task）”

Question

我正在尝试将Firebase登录名添加到我的Android Studio代码中，但是onCompleteListener给出错误。

package tribunecomp.com.firebasefacebooklogin;

import android.content.Intent;
import android.support.annotation.NonNull;
import android.support.v7.app.AppCompatActivity;
import android.os.Bundle;
import android.util.Log;
import android.widget.Toast;

import com.facebook.AccessToken;
import com.facebook.CallbackManager;
import com.facebook.FacebookCallback;
import com.facebook.FacebookException;
import com.facebook.login.LoginResult;
import com.facebook.login.widget.LoginButton;
import com.google.android.gms.tasks.OnCompleteListener;
import com.google.firebase.auth.AuthCredential;
import com.google.firebase.auth.AuthResult;
import com.google.firebase.auth.FacebookAuthProvider;
import com.google.firebase.auth.FirebaseAuth;
import com.google.firebase.auth.FirebaseUser;

public class MainActivity extends AppCompatActivity  {

private CallbackManager mCallbackManager;
private static final String TAG = "FACELOG";
private FirebaseAuth mAuth;


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

    // ...
    // Initialize Firebase Auth
    mAuth = FirebaseAuth.getInstance();

    // Initialize Facebook Login button
    mCallbackManager = CallbackManager.Factory.create();
    LoginButton loginButton = findViewById(R.id.login_button);
    loginButton.setReadPermissions("email", "public_profile");
    loginButton.registerCallback(mCallbackManager, new FacebookCallback<LoginResult>() {
        @Override
        public void onSuccess(LoginResult loginResult) {
            Log.d(TAG, "facebook:onSuccess:" + loginResult);
            handleFacebookAccessToken(loginResult.getAccessToken());
        }

        @Override
        public void onCancel() {
            Log.d(TAG, "facebook:onCancel");
            // ...
        }

        @Override
        public void onError(FacebookException error) {
            Log.d(TAG, "facebook:onError", error);
            // ...
        }
    });

}

@Override
protected void onActivityResult(int requestCode, int resultCode, Intent data) {
    super.onActivityResult(requestCode, resultCode, data);

    // Pass the activity result back to the Facebook SDK
    mCallbackManager.onActivityResult(requestCode, resultCode, data);
}
private void handleFacebookAccessToken(AccessToken token) {
    Log.d(TAG, "handleFacebookAccessToken:" + token);

    AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
    mAuth.signInWithCredential(credential)
            .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, "signInWithCredential:success");
                        FirebaseUser user = mAuth.getCurrentUser();
                        updateUI(user);
                    } else {
                        // If sign in fails, display a message to the user.
                        Log.w(TAG, "signInWithCredential:failure", task.getException());
                        Toast.makeText(FacebookLoginActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                        updateUI(null);
                    }

                    // [START_EXCLUDE]
                    hideProgressDialog();
                    // [END_EXCLUDE]
                }
            });
}

@Override
public void onStart() {
    super.onStart();
    // Check if user is signed in (non-null) and update UI accordingly.
    FirebaseUser currentUser = mAuth.getCurrentUser();
    if (currentUser != null) {
        updateUI();
    }
}

private void updateUI() {
    Toast.makeText(MainActivity.this, "You're logged in", Toast.LENGTH_LONG).show();
}

}

在handleFacebookAccesstoken方法上出错

 private void handleFacebookAccessToken(AccessToken token) {
        Log.d(TAG, "handleFacebookAccessToken:" + token);

    AuthCredential credential = FacebookAuthProvider.getCredential(token.getToken());
    mAuth.signInWithCredential(credential)
            .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, "signInWithCredential:success");
                        FirebaseUser user = mAuth.getCurrentUser();
                        updateUI(user);
                    } else {
                        // If sign in fails, display a message to the user.
                        Log.w(TAG, "signInWithCredential:failure", task.getException());
                        Toast.makeText(FacebookLoginActivity.this, "Authentication failed.",
                                Toast.LENGTH_SHORT).show();
                        updateUI(null);
                    }

                    // [START_EXCLUDE]
                    hideProgressDialog();
                    // [END_EXCLUDE]
                }
            });
}

错误说： “从OnCompleteListener派生的匿名类”类必须声明为抽象，或在OnCompleteListener中实现抽象方法“ onComplete（Task）”