Firebase数据库数据在读取时返回空值 [英] Firebase Database Data Returning Null When Reading

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问题描述

我不知道为什么，我已经探索了 .setValue（）和 .updateChildren（）方法，但无论什么原因，当我从Firebase读取数据时，它将返回null。以下是我写给Firebase的信息：

模型民意调查班： 

  @IgnoreExtraProperties 
 public class Poll {
 
 private String question; 
私人字符串image_URL; 
 $ b $ public Poll（）{
} 
 
 public Poll（String Question，String Image_URL）{
 this.question = Question; 
 this.image_URL = Image_URL; 
} 
 
 public String getQuestion（）{
 return question; 
} 
 
 public void setQuestion（String question）{
 this.question = question; 
} 
 
 public String getImage_URL（）{
 return image_URL; 
 
 
 public void setImage_URL（String image_URL）{
 this.image_URL = image_URL; 
} 
 
 @Exclude 
 public Map< String，Object> toMap（）{
 HashMap< String，Object> result = new HashMap<>（）; 
 result.put（问题，问题）; 
 result.put（image_URL，image_URL）; 
返回结果; 
 
 
 $ b $ / code $ / pre 
 $ b我是按照文档<  here   .toMap（）方法和使用 .updateChildren（） 
 
 
 
这里是我创建我的Firebase引用并写入数据库：
 
 $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $ $保护无效的onCreate（Bundle savedInstanceState）{
 super.onCreate（savedInstanceState）; 
 setContentView（R.layout.activity_create）; 
 mStorage = FirebaseStorage.getInstance（）; 
 mStorageRef = mStorage.getReferenceFromUrl（gs：//firebase-fan-polls.appspot.com）; 
 
 
 mBaseRef = FirebaseDatabase.getInstance（）。getReference（）; 
 mPollsRef = mBaseRef.child（Polls）; 
 mAddImageButton =（FloatingActionButton）findViewById（R.id.add_image_button）; 
 mAddAnswersButton =（ImageView）findViewById（R.id.add_answers_button）; 
 mImagePreview =（ImageView）findViewById（R.id.preview_image）; 
 mCreatePollQuestion =（EditText）findViewById（R.id.create_poll_question_editText）; 
 mCreatePollAnswerCounter =（TextView）findViewById（R.id.create_poll_answer_counter_TextView）; 
 mEditTextAnswerLayout =（ViewGroup）findViewById（R.id.create_poll_questions_answer_layout）; 
 mSubmitPollCreation =（FloatingActionButton）findViewById（R.id.submit_poll_FAB）; 
 mNumberOfPollAnswersCreatedByUser = 2; 
 mAnswerChoices = new ArrayList<>（）; 
 mCreatePollAnswerCounter.setText（String.valueOf（mNumberOfPollAnswersCreatedByUser））; 
 for（int i = 0; i< mNumberOfPollAnswersCreatedByUser; i ++）{
 createAnswerChoice（i + 1）; 
 
 mAddAnswersButton.setOnClickListener（new View.OnClickListener（）{
 @Override 
 public void onClick（View v）{
 mNumberOfPollAnswersCreatedByUser ++; 
 if （）; 
 return; 
} 
 createAnswerChoice（） mNumberOfPollAnswersCreatedByUser）; 
 mCreatePollAnswerCounter.setText（String.valueOf（mNumberOfPollAnswersCreatedByUser））; 
} 
}）; 
 
 mSubmitPollCreation.setOnClickListener（new View.OnClickListener（）{
 @Override 
 public void onClick（View v）{
 
 // TODO：Need检查是否添加投票要求，即问题，答案，...... 
 //检查图像是否已经被加载
 if（resultImageURL == null）{
 Toast。 makeText（getApplicationContext（），getResources（）.getString（R.string.no_image_selected），Toast.LENGTH_LONG）.show（）; 
 return; 
} 
 
轮询轮询= new Poll（mCreatePollQuestion.getText（）。toString（），resultImageURL）; 
 Map< String，Object> pollMap = poll.toMap（）; 
 String key = mBaseRef.child（Polls） （）; 
 MapUp< String，Object> childUpdates = new HashMap< String，Object>（）; 
 childUpdates.put（/ Polls /+ key，pollMap）; 
 mBaseRef.updateChildren（childUpdates ）; 
 
 $ b if（mNumberOfPollAnswersCreatedByUser> 5）{
 Toast.makeText（getApplicationContext（），getResources（）.getText（R.string.poll_answers_greater_than_five），Toast.LENGTH_LONG）显示（）; 
 mNumberOfPollAnswersCreatedByUser = 5; 
} 
 
 Intent toHomeActivity = new Intent（CreateActivity.this，HomeActivity.class）; 
 toHomeActivity.putExtra（viewpager_position，2）; 
 startActivity（toHomeActivity）; 
} 
}）;

所有内容都正确写入到Firebase中，正如我在控制台的数据库中看到的一样。我尝试从这个活动中读取它：
public class PollFragment extends Fragment {

  @Bind（R.id。 comment_label_counter）
 TextView mCommentCounter; 
 
 @Bind（R.id.comments_label_icon）
 ImageView mCommentsLabelIcon; 
 
 private DatabaseReference mBaseRef; 
 private DatabaseReference mPollsRef; 
 private DatabaseReference mSelectedPollRef; 
 
私人RadioGroup mPollQuestionRadioGroup; 
私人RadioGroup.LayoutParams mParams; 
 
 //静态
私有TextView mCommentsLabel; 
私人TextView mTotalVoteCounter; 
私人TextView mSelectedVote; 
私人TextView mYourVotelabel; 
私人ViewPager mViewPager; 
 private int mPagerCurrentPosition; 
 private static final String VOTE_COUNT_LABEL =Vote_Count; 
 private static final String QUESTION_LABEL =question; 
 private static final String ANSWERS_LABEL =Answers; 
 private static final String POLL_LABEL =Poll; 
 private static final String IMAGE_URL =image_URL; 
 
 //所有日期项目;动态
私人DateFormat mDateFormat; 
私人日期mDate; 
 private String mCurrentDateString; 
私人TextView mPollQuestion; 
 private ArrayList< RadioButton> mPollAnswerArrayList; 
 private Horizo​​ntalBarChart mPollResults; 
 ArrayList< BarEntry> pollResultChartValues; 
私人BarDataSet数据; 
 private ArrayList< IBarDataSet>数据集; 
 private ValueEventListener valueEventListener; 
私人字符串pollID; 
 private int mPollIndex; 
私人ProgressBar mProgressBar; 
 
 private OnFragmentInteractionListener mListener; 
 $ b $ public PollFragment（）{
 //必需的空公共构造函数
 
 $ b $ ** 
 *使用此工厂方法创建
 *这个片段的新实例使用提供的参数。 
 * 
 * @return片段PollFragment的新实例。 
 * / 
 // TODO：重命名并更改参数的类型和数量
 // TODO：决定添加注释按钮的位置; 
 public static PollFragment newInstance（String pollIndex）{
 PollFragment fragment = new PollFragment（）; 
 Bundle args = new Bundle（）; 
 args.putString（POLL_ID，pollIndex）; 
 fragment.setArguments（args）; 
 return fragment; 
 
 
 $ b @Override 
 public void onCreate（Bundled savedInstanceState）{
 super.onCreate（savedInstanceState）; 
 
 // TODO：检查导航，看看是否有不同的ID从趋势，跟随和新的片段生成
 Bundle args = getArguments（）; 
 String pollID = args.getString（POLL_ID）; 
 Log.v（TAG，PASSED ID is+ pollID）; 
 mBaseRef = FirebaseDatabase.getInstance（）。getReference（）; 
 mPollsRef = mBaseRef.child（POLL_LABEL）; 
 mSelectedPollRef = mPollsRef.child（pollID）; 
 
 
 $ b @Override 
 public view onCreateView（LayoutInflater inflater，ViewGroup container，
 Bundled savedInstanceState）{
 // TODO：Add片段代码来检查savedInstanceState == null;在活动级别添加？ 
 
 
 //膨胀这个片段的布局
 final ViewGroup rootView =（ViewGroup）inflater.inflate（R.layout.fragment_poll，container，false）; 
 ButterKnife.bind（this，rootView）; 
 getActivity（）。setTitle（R.string.todays_polls_title）; 
 
 //初始化轮询结果条形图并设置为不可见
 mPollResults =（Horizo​​ntalBarChart）rootView.findViewById（R.id.poll_results_chart）; 
 mPollResults.setBackgroundColor（getResources（）。getColor（R.color.white））; 
 mPollResults.setNoDataTextDescription（getResources（）。getString（R.string.no_results_description））; 
 mPollResults.setVisibility（View.INVISIBLE）; 
 
 mTotalVoteCounter =（TextView）rootView.findViewById（R.id.total_vote_counter）; 
 mCommentCounter =（TextView）rootView.findViewById（R.id.comment_label_counter）; 
 mCommentCounter =（TextView）rootView.findViewById（R.id.comment_label_counter）; 
 
 mProgressBar =（ProgressBar）rootView.findViewById（R.id.progress_bar_white）; 
 
 mPollQuestion =（TextView）rootView.findViewById（R.id.poll_question）; 
 mPollQuestion.setTextSize（TypedValue.COMPLEX_UNIT_PX，getResources（）。getDimension（R.dimen.poll_question_text_size））; 
 mPollQuestionRadioGroup =（RadioGroup）rootView.findViewById（R.id.poll_question_group）; 
 
 
 $ b mSelectedPollRef.addListenerForSingleValueEvent（new ValueEventListener（）{
 @Override 
 public void onDataChange（DataSnapshot dataSnapshot）{
 
 Log.v（TAG，dataSnapshot.getKey（））; 
 
 //添加问题
字符串pollQuestion =（String）dataSnapshot.child（QUESTION_LABEL）.getValue（）; 
 Log.v（TAG，POLL QUESTION IS+ pollQuestion）; 
 mPollQuestion.setText（pollQuestion）; 
 mPollQuestion.setTypeface（null，Typeface.BOLD）; 
 
 
 $ b //添加图片
字符串pollImageURL =（String）dataSnapshot.child（IMAGE_URL）.getValue（）; 
 Log.v（TAG， poll image image URL+ pollImageURL）; 
 Picasso.with（getActivity（））
 .load（pollImageURL）
 .fit（）
 .placeholder（R.drawable .loading_spinner_white）
 。（（ImageView）rootView.findViewById（R.id.poll_image））;

最后，这是我的Firebase数据库：

解决方案

不小心的错误： 

  private static final String POLL_LABEL =Poll;

应该是： 

  private static final String POLL_LABEL =Polls;

第一个选择不是正确的Firebase引用，从而导致错误。 b

I am not sure why, I have explored both .setValue() and .updateChildren() methods, but for whatever reason when I read data from firebase it is returning null. Here is how I write to Firebase:

Model Poll Class:

@IgnoreExtraProperties
public class Poll {

private String question;
private String image_URL;

public Poll() {
}

public Poll(String Question, String Image_URL) {
    this.question = Question;
    this.image_URL = Image_URL;
}

public String getQuestion() {
    return question;
}

public void setQuestion(String question) {
    this.question = question;
}

public String getImage_URL() {
    return image_URL;
}

public void setImage_URL(String image_URL) {
    this.image_URL = image_URL;
}

@Exclude
public Map<String, Object> toMap(){
            HashMap<String, Object> result = new HashMap<>();
            result.put("question", question);
            result.put("image_URL", image_URL);
            return result;
     }

   }

*I am following the documentation here with my .toMap() method and use of .updateChildren()

Here is where I create my Firebase references and write to the database:

 @Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.activity_create);
    mStorage = FirebaseStorage.getInstance();
    mStorageRef = mStorage.getReferenceFromUrl("gs://firebase-fan-polls.appspot.com");


    mBaseRef = FirebaseDatabase.getInstance().getReference();
    mPollsRef = mBaseRef.child("Polls");
    mAddImageButton = (FloatingActionButton) findViewById(R.id.add_image_button);
    mAddAnswersButton = (ImageView) findViewById(R.id.add_answers_button);
    mImagePreview = (ImageView) findViewById(R.id.preview_image);
    mCreatePollQuestion = (EditText) findViewById(R.id.create_poll_question_editText);
    mCreatePollAnswerCounter = (TextView) findViewById(R.id.create_poll_answer_counter_TextView);
    mEditTextAnswerLayout = (ViewGroup) findViewById(R.id.create_poll_questions_answer_layout);
    mSubmitPollCreation = (FloatingActionButton) findViewById(R.id.submit_poll_FAB);
    mNumberOfPollAnswersCreatedByUser = 2;
    mAnswerChoices = new ArrayList<>();
    mCreatePollAnswerCounter.setText(String.valueOf(mNumberOfPollAnswersCreatedByUser));
    for (int i = 0; i < mNumberOfPollAnswersCreatedByUser; i++) {
        createAnswerChoice(i + 1);
    }
    mAddAnswersButton.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {
            mNumberOfPollAnswersCreatedByUser++;
            if (mNumberOfPollAnswersCreatedByUser > 5) {
                Toast.makeText(getApplicationContext(), R.string.max_create_answers, Toast.LENGTH_SHORT).show();
                return;
            }
            createAnswerChoice(mNumberOfPollAnswersCreatedByUser);
            mCreatePollAnswerCounter.setText(String.valueOf(mNumberOfPollAnswersCreatedByUser));
        }
    });

    mSubmitPollCreation.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View v) {

            //TODO: Need to check if poll requirements are added, i.e. Question, Answer, ......
            //check if image has been loaded first
            if (resultImageURL == null) {
                Toast.makeText(getApplicationContext(), getResources().getString(R.string.no_image_selected), Toast.LENGTH_LONG).show();
                return;
            }

            Poll poll = new Poll(mCreatePollQuestion.getText().toString(), resultImageURL);
            Map <String, Object> pollMap = poll.toMap();
            String key = mBaseRef.child("Polls").push().getKey();
            Map<String, Object> childUpdates = new HashMap<String, Object>();
            childUpdates.put("/Polls/" + key, pollMap);
            mBaseRef.updateChildren(childUpdates);


            if (mNumberOfPollAnswersCreatedByUser > 5) {
                Toast.makeText(getApplicationContext(), getResources().getText(R.string.poll_answers_greater_than_five), Toast.LENGTH_LONG).show();
                mNumberOfPollAnswersCreatedByUser = 5;
            }

            Intent toHomeActivity = new Intent(CreateActivity.this, HomeActivity.class);
            toHomeActivity.putExtra("viewpager_position", 2);
            startActivity(toHomeActivity);
        }
    });

Everything is writing to Firebase correctly, as I can see it in the database in my console. I try and read it from this activity: public class PollFragment extends Fragment {

@Bind(R.id.comment_label_counter)
TextView mCommentCounter;

@Bind(R.id.comments_label_icon)
ImageView mCommentsLabelIcon;

private DatabaseReference mBaseRef;
private DatabaseReference mPollsRef;
private DatabaseReference mSelectedPollRef;

private RadioGroup mPollQuestionRadioGroup;
private RadioGroup.LayoutParams mParams;

//static
private TextView mCommentsLabel;
private TextView mTotalVoteCounter;
private TextView mSelectedVote;
private TextView mYourVotelabel;
private ViewPager mViewPager;
private int mPagerCurrentPosition;
private static final String VOTE_COUNT_LABEL = "Vote_Count";
private static final String QUESTION_LABEL = "question";
private static final String ANSWERS_LABEL = "Answers";
private static final String POLL_LABEL = "Poll";
private static final String IMAGE_URL = "image_URL";

//all date items; dynamic
private DateFormat mDateFormat;
private Date mDate;
private String mCurrentDateString;
private TextView mPollQuestion;
private ArrayList<RadioButton> mPollAnswerArrayList;
private HorizontalBarChart mPollResults;
ArrayList<BarEntry> pollResultChartValues;
private BarDataSet data;
private ArrayList<IBarDataSet> dataSets;
private ValueEventListener valueEventListener;
private String pollID;
private int mPollIndex;
private ProgressBar mProgressBar;

private OnFragmentInteractionListener mListener;

public PollFragment() {
    // Required empty public constructor
}

/**
 * Use this factory method to create a new instance of
 * this fragment using the provided parameters.
 *
 * @return A new instance of fragment PollFragment.
 */
// TODO: Rename and change types and number of parameters
// TODO: Decide where to add comments button;
public static PollFragment newInstance(String pollIndex) {
    PollFragment fragment = new PollFragment();
    Bundle args = new Bundle();
    args.putString("POLL_ID", pollIndex);
    fragment.setArguments(args);
    return fragment;
}


@Override
public void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);

    //TODO: check navigation to see if there are different ID's being generated from trending, following, and new fragments
    Bundle args = getArguments();
    String pollID = args.getString("POLL_ID");
    Log.v("TAG", "THE PASSED ID Is " + pollID);
    mBaseRef = FirebaseDatabase.getInstance().getReference();
    mPollsRef = mBaseRef.child(POLL_LABEL);
    mSelectedPollRef = mPollsRef.child(pollID);

}

@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container,
                         Bundle savedInstanceState) {
    // TODO: Add Fragment Code to check if savedInstanceState == null; add at Activity Level?


    // Inflate the layout for this fragment
    final ViewGroup rootView = (ViewGroup) inflater.inflate(R.layout.fragment_poll, container, false);
    ButterKnife.bind(this, rootView);
    getActivity().setTitle(R.string.todays_polls_title);

    //Initialize Poll Results Bar Chart and set to Invisible
    mPollResults = (HorizontalBarChart) rootView.findViewById(R.id.poll_results_chart);
    mPollResults.setBackgroundColor(getResources().getColor(R.color.white));
    mPollResults.setNoDataTextDescription(getResources().getString(R.string.no_results_description));
    mPollResults.setVisibility(View.INVISIBLE);

    mTotalVoteCounter = (TextView) rootView.findViewById(R.id.total_vote_counter);
    mCommentCounter = (TextView) rootView.findViewById(R.id.comment_label_counter);
    mCommentCounter = (TextView) rootView.findViewById(R.id.comment_label_counter);

    mProgressBar = (ProgressBar) rootView.findViewById(R.id.progress_bar_white);

    mPollQuestion = (TextView) rootView.findViewById(R.id.poll_question);
    mPollQuestion.setTextSize(TypedValue.COMPLEX_UNIT_PX, getResources().getDimension(R.dimen.poll_question_text_size));
    mPollQuestionRadioGroup = (RadioGroup) rootView.findViewById(R.id.poll_question_group);



    mSelectedPollRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {

            Log.v("TAG", dataSnapshot.getKey());

            //add question
            String pollQuestion = (String) dataSnapshot.child(QUESTION_LABEL).getValue();
            Log.v("TAG", "THE POLL QUESTION IS " + pollQuestion);
            mPollQuestion.setText(pollQuestion);
            mPollQuestion.setTypeface(null, Typeface.BOLD);



            //add image
            String pollImageURL = (String) dataSnapshot.child(IMAGE_URL).getValue();
            Log.v("TAG", "THE POLL IMAGE URL IS" + pollImageURL);
            Picasso.with(getActivity())
                    .load(pollImageURL)
                    .fit()
                    .placeholder(R.drawable.loading_spinner_white)
                    .into((ImageView) rootView.findViewById(R.id.poll_image));

Finally, here is my Firebase Database:

解决方案

Careless mistake:

private static final String POLL_LABEL = "Poll";

Should be:

private static final String POLL_LABEL = "Polls";

The first choice was not the correct Firebase referencing thus causing the error.

这篇关于Firebase数据库数据在读取时返回空值的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！

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