Question

我有一个基于Firebase监听器更新的动态ListView。我最初填充ListView，然后当项目添加到Firebase时，我调用notifySetDataChanged（）来更新ListView。

代码：

public class Discussion_Activity extends AppCompatActivity {

private ImageView mPollImage;
private TextView mPollCommentQuestion;

private EditText mUserComment;
private String mUserID;
private ImageView mUserAvatar;
private ListView mPollCommentsList;
private ArrayAdapter<Comments> mCommentAdapter;
private int mNumberOfCommentsAtPoll;
private ArrayList<Comments> mCommentArrayList;
private ArrayList<String> mCommentIDArrayList;

private Firebase mBaseRef;
private Firebase mPollsRef;
private Firebase mUpdateRef;
private Firebase mCommentsRef;

private DateFormat mDateFormat;
private Date mDate;
private String mCurrentDateString;

private int mPollIndex;

private ChildEventListener mUpdateComments;

private Toolbar toolbar;


private static final String FIREBASE_URL = "https://fan-polls.firebaseio.com/";
private static final String COMMENTS_LABEL = "Comments";
private static final String POLLS_LABEL = "Polls";

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    Firebase.setAndroidContext(this);
    setContentView(R.layout.activity_discussion);
    toolbar = (Toolbar) findViewById(R.id.tool_bar);
    setSupportActionBar(toolbar);
    setTitle(R.string.discussion_title_text);

    mDateFormat = new SimpleDateFormat("MM-dd-yyyy");
    mDate = new Date();
    mCurrentDateString = mDateFormat.format(mDate);

    mBaseRef = new Firebase(FIREBASE_URL);
    mPollsRef = mBaseRef.child(POLLS_LABEL);

    mPollImage = (ImageView) findViewById(R.id.comments_image);
    mPollCommentQuestion = (TextView) findViewById(R.id.poll_comment_question);

    mUserComment = (EditText) findViewById(R.id.user_comment);
    mUserAvatar = (ImageView) findViewById(R.id.profile_image_avatar);
    mPollCommentsList = (ListView) findViewById(R.id.poll_comments_list);
    mCommentArrayList = new ArrayList<Comments>();
    mCommentIDArrayList = new ArrayList<String>();
    mCommentAdapter = new ListAdapter(getApplicationContext(), R.layout.individual_comment, mCommentArrayList);
    mPollCommentsList.setAdapter(mCommentAdapter);
    getWindow().setSoftInputMode(WindowManager.LayoutParams.SOFT_INPUT_STATE_HIDDEN);

    Intent intent = getIntent();
    String pollID = intent.getStringExtra("POLL_ID");
    mPollIndex = intent.getIntExtra("POLL_INDEX", 0);
    mUpdateRef = mPollsRef.child(mCurrentDateString).child(String.valueOf(mPollIndex + 1));
    mCommentsRef = mUpdateRef.child(COMMENTS_LABEL);


    mUpdateRef.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            setImage(dataSnapshot);
            setQuestion(dataSnapshot);
            createInitialCommentArray(dataSnapshot);
            mNumberOfCommentsAtPoll = (int) dataSnapshot.child(COMMENTS_LABEL).getChildrenCount();
            for (int i = 0; i < mNumberOfCommentsAtPoll; i++){
                String commentID = (String) dataSnapshot.child(COMMENTS_LABEL).child(mCommentIDArrayList.get(i)).child("COMMENT").getValue();
                Log.v("COMMENT_ID", "The comment ID is " + commentID);
                String userID = (String) dataSnapshot.child(COMMENTS_LABEL).child(mCommentIDArrayList.get(i)).child("USER_ID").getValue();
                Log.v("USER_ID", "The user ID is " + userID);
                mCommentArrayList.add(new Comments(mUserAvatar, userID, commentID));
                mCommentAdapter.notifyDataSetChanged();
            }

        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    });

    //TODO: Store unique comment ID's in an array

    //TODO: Figure out how to programmatically add images to AWS and then store URL in Firebase
    ImageView fab = (ImageView) findViewById(R.id.add_comment);
    fab.setOnClickListener(new View.OnClickListener() {
        @Override
        public void onClick(View view) {
            HashMap<String, Object> commentMap = new HashMap<String, Object>();
            commentMap.put("USER_ID", mBaseRef.getAuth().getUid());
            commentMap.put("COMMENT", mUserComment.getText().toString());
            mUpdateRef.child(COMMENTS_LABEL).push().updateChildren(commentMap);
            mCommentAdapter.notifyDataSetChanged();

            hideKeyboard(view);
            mUserComment.setText("");
            Toast.makeText(getApplicationContext(),R.string.comment_added, Toast.LENGTH_LONG).show();
        }
    });
}


//How to iterate through a Firbease database
private void createInitialCommentArray(DataSnapshot dataSnapshot) {
    for (DataSnapshot s : dataSnapshot.child(COMMENTS_LABEL).getChildren()) {
        mCommentIDArrayList.add(s.getKey());
        Log.v("COMMENT_ARRAY", "The comment array is " + s.getKey());
    }
}

@Override
protected void onStart() {
    super.onStart();
    mUpdateComments = new ChildEventListener() {
        @Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {
            mCommentIDArrayList.add(dataSnapshot.getKey());
            String commentID = (String) dataSnapshot.child("COMMENT").getValue();
            Log.v("New_Comment", "The new comment is " + commentID);
            String userID = (String) dataSnapshot.child("USER_ID").getValue();
            Log.v("New_User_ID", "The new userID is " + userID);
            mCommentArrayList.add(new Comments(mUserAvatar, userID, commentID));
            mCommentAdapter.notifyDataSetChanged();
        }

        @Override
        public void onChildChanged(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onChildRemoved(DataSnapshot dataSnapshot) {

        }

        @Override
        public void onChildMoved(DataSnapshot dataSnapshot, String s) {

        }

        @Override
        public void onCancelled(FirebaseError firebaseError) {

        }
    };

    //TODO: Keep listeners lean; only add listener to the specific root of the data
    mCommentsRef.addChildEventListener(mUpdateComments);

    }

@Override
protected void onStop() {
    super.onStop();
    mCommentsRef.removeEventListener(mUpdateComments);
}

private void setQuestion(DataSnapshot dataSnapshot) {
    String pollQuestion = (String) dataSnapshot.child("Poll_Question").getValue();
    if ((getResources().getConfiguration().screenLayout & Configuration.SCREENLAYOUT_SIZE_MASK) == Configuration.SCREENLAYOUT_SIZE_XLARGE) {
        mPollCommentQuestion.setTextSize(24);
    } else if ((getResources().getConfiguration().screenLayout & Configuration.SCREENLAYOUT_SIZE_MASK) == Configuration.SCREENLAYOUT_SIZE_LARGE) {
        mPollCommentQuestion.setTextSize(18);
    } else if ((getResources().getConfiguration().screenLayout & Configuration.SCREENLAYOUT_SIZE_MASK) == Configuration.SCREENLAYOUT_SIZE_NORMAL) {
        mPollCommentQuestion.setTextSize(14);
    } else if ((getResources().getConfiguration().screenLayout & Configuration.SCREENLAYOUT_SIZE_MASK) == Configuration.SCREENLAYOUT_SIZE_SMALL) {
        mPollCommentQuestion.setTextSize(14);
    }
    mPollCommentQuestion.setText(pollQuestion);
}

public void hideKeyboard(View view) {
    InputMethodManager inputMethodManager = (InputMethodManager) getSystemService(Activity.INPUT_METHOD_SERVICE);
    inputMethodManager.hideSoftInputFromWindow(view.getWindowToken(), 0);
}

适配器 -

    public class ListAdapter extends ArrayAdapter<Comments> {

        public ListAdapter(Context context, int textViewResourceId) {
            super(context, textViewResourceId);
        }

        public ListAdapter(Context context, int resource, List<Comments> items) {
            super(context, resource, items);
        }

        @Override
        public int getCount() {
            return mNumberOfCommentsAtPoll;
        }

        @Override
        public View getView(int position, View convertView, ViewGroup parent) {

            View v = convertView;

            if (v == null) {
                LayoutInflater vi;
                vi = LayoutInflater.from(getContext());
                v = vi.inflate(R.layout.individual_comment, null);
            }

            Comments p = getItem(position);

            if (p != null) {
                TextView userID = (TextView) v.findViewById(R.id.user_ID);
                TextView userComment = (TextView) v.findViewById(R.id.user_comment);

                if (userID != null) {
                    userID.setText(p.getUserID());
                }

                if (userComment != null) {
                    userComment.setText(p.getUserComment());
                }
            }


            return v;
        }

    }

    private void setImage(DataSnapshot dataSnapshot) {
        String imageURL = (String) dataSnapshot.child("Image").getValue();
        Picasso.with(getApplicationContext())
                .load(imageURL)
                .transform(new RoundedTransformation(10, 6))
                .fit()
                .into((mPollImage));
        mPollImage.setColorFilter(Color.argb(140, 255, 255, 255)); // White Tint
    }

}

Answer 1

您使用了addListenerForSingleValueEvent()，它只会被调用一次，并且在被调用后会被取消注册。因此，如果您更改了firebase数据库中的数据（正如您在fab onclick中所做的那样），那么当您的监听器不再注册时，您将无法获得更改数据的回调。

对于您的任务，您需要使用addValueEventListener()或实现Child事件侦听器。是的，不要忘记在不再需要它时删除它们。您的onChildAdded()存在问题。

String commentID = (String) dataSnapshot.child(COMMENTS_LABEL).child(pollCount).child("COMMENT").getValue();
String userID = (String) dataSnapshot.child(COMMENTS_LABEL).child(pollCount).child("USER_ID").getValue();

以上陈述的行为不会像您期望的那样。根据您的工厂fab.setOnClickListener()，您将生成随机唯一键作为COMMENTS_LABEL的子项，并且该键包含您的user_id和注释。

但是你试图使用索引0,1,2等从COMMENTS_LABEL的子节点获取user_id和注释。这将永远不会获取您保存的确切值，因为您不知道什么是唯一ID。你需要像这样改变onChildAdded() -

@Override
        public void onChildAdded(DataSnapshot dataSnapshot, String s) {

            String commentID = (String) dataSnapshot.child(COMMENTS_LABEL).child(dataSnapshot.getKey()).child("COMMENT").getValue();
            String userID = (String) dataSnapshot.child(COMMENTS_LABEL).child(dataSnapshot.getKey()).child("USER_ID").getValue();
            mCommentArrayList.add(new Comments(mUserAvatar, userID, commentID));
            mCommentAdapter.notifyDataSetChanged();
        }

动态ListView项不填充XML

1 个答案: