非法状态异常Firebase数据库

我正在尝试使用Firebase数据库但面临非法状态异常

默认FirebaseApp未在此过程com.example中初始化 . 确保首先调用FirebaseApp.initializeApp（Context） .

我创建了一个可以从任何地方实例化的Utility类 . 我已经尝试过Application和Activity（onCreate）级别，结果是一样的 .

public class FirebaseUtils {
    private static final String TAG = FirebaseUtils.class.getSimpleName();

    private static FirebaseDatabase mFirebaseDatabase;
    private static DatabaseReference mDbReference;

    // listeners
    private static OnFirebaseValueListener mFirebaseValueListener;

    /**
     * Method is used to set callback to listen to value changes in Firebase DB
     *
     * @param listener
     */
    public static void onFirebaseValueListener(OnFirebaseValueListener listener) {
        mFirebaseValueListener = listener;
    }

    /**
     * Constructor
     */
    public FirebaseUtils(Context context) {
        FirebaseApp.initializeApp(context);
        mFirebaseDatabase = FirebaseDatabase.getInstance();
        mDbReference = mFirebaseDatabase.getReference();
    }

    /**
     * Method is used to add a list of values to Firebase DB
     *
     * @param alHistory
     */
    public static void addValues(List<?> alHistory) {
        if (!FrameworkUtils.checkIfNull(mDbReference)) {
            // set value
            mDbReference.setValue(alHistory);
            mDbReference.addValueEventListener(new ValueEventListener() {
                @Override
                public void onDataChange(DataSnapshot dataSnapshot) {
                    Log.i(TAG, "<onDataChange> successful!");
                    if (!FrameworkUtils.checkIfNull(mFirebaseValueListener)) {
                        mFirebaseValueListener.onDataChange(dataSnapshot);
                    }
                }

                @Override
                public void onCancelled(DatabaseError databaseError) {
                    if (!FrameworkUtils.checkIfNull(databaseError) && !FrameworkUtils.isStringEmpty(databaseError.getMessage())) {
                        Log.i(TAG, "<onCancelled> error: " + databaseError.getMessage());
                        if (!FrameworkUtils.checkIfNull(mFirebaseValueListener)) {
                            mFirebaseValueListener.onCancelled(databaseError);
                        }
                    }
                }
            });
        }
    }

    /**
     * Method is used to retrieve a list of values from Firebase DB
     */
    public static void retrieveValues() {
        mDbReference.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                Log.i(TAG, "<onDataChange> successful!");
                if (!FrameworkUtils.checkIfNull(mFirebaseValueListener)) {
                    mFirebaseValueListener.onDataChange(dataSnapshot);
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {
                if (!FrameworkUtils.checkIfNull(databaseError) && !FrameworkUtils.isStringEmpty(databaseError.getMessage())) {
                    Log.i(TAG, "<onCancelled> error: " + databaseError.getMessage());
                    if (!FrameworkUtils.checkIfNull(mFirebaseValueListener)) {
                        mFirebaseValueListener.onCancelled(databaseError);
                    }
                }
            }
        });
    }
}

我正在这样实例化

// instantiate FirebaseUtils
        new FirebaseUtils(this);

我在gradle中添加了所有依赖项

dependencies {       
     compile 'com.google.firebase:firebase-database:10.2.1'
}

我在Manifest上有互联网许可

<uses-permission android:name="android.permission.INTERNET" />

Firebase上是否存在某种我缺失的设置？