java - 如何修复 RecyclerView : No adapter attached; skipping layout?

Question

我已经这样做有一段时间了，但我不断收到错误:E/RecyclerView: No adapter attached; skipping layout 。

我开始更改调用 setAdapter 的 ViewProfilePostsFragment 中的内容，但我没有成功使其工作。我似乎无法弄清楚为什么会发生这种情况。

这是我的脚本，以便您可以告诉我我做错了什么，其中一个脚本调用 setAdapter 方法，另一个脚本调用 RecyclerAdapter 脚本。

ViewProfilePostsFragment.java

public class ViewProfilePostsFragment extends Fragment{
private static final String TAG = "ViewProfilePostsFragmen";

private ArrayList<Photo> mPhotos;
private ArrayList<String> mFriends;
private RecyclerView mRecView;
private ViewProfilePostsAdapter mAdapter;

@Nullable
@Override
public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_profile_posts, container, false);
    mRecView = (RecyclerView) view.findViewById(R.id.lvProfilePosts);
    mFriends = new ArrayList<>();
    mPhotos = new ArrayList<>();

    getFriends();


    return view;
}

private void getFriends(){
    Log.d(TAG, "getFollowing: searching for FRIENDS **************************************");

    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    Query query = reference
            .child(getString(R.string.dbname_friends))
            .child(FirebaseAuth.getInstance().getCurrentUser().getUid());
    query.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
                mFriends.add(singleSnapshot.child(getString(R.string.field_user_id)).getValue().toString());
            }
            //get the photos
            getPhotos();
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

private void getPhotos(){
    Log.d(TAG, "getPhotos: getting photos");
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    for(int i = 0; i < mFriends.size(); i++){
        final int count = i;
        Query query = reference
                .child(getString(R.string.dbname_user_photos))
                .child(mFriends.get(i))
                .orderByChild(getString(R.string.field_user_id))
                .equalTo(mFriends.get(i));
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){

                    Photo photo = new Photo();
                    Map<String, Object> objectMap = (HashMap<String, Object>) singleSnapshot.getValue();

                    photo.setCaption(objectMap.get(getString(R.string.field_caption)).toString());
                    photo.setTags(objectMap.get(getString(R.string.field_tags)).toString());
                    photo.setPhoto_id(objectMap.get(getString(R.string.field_photo_id)).toString());
                    photo.setUser_id(objectMap.get(getString(R.string.field_user_id)).toString());
                    photo.setDate_created(objectMap.get(getString(R.string.field_date_created)).toString());
                    photo.setImage_path(objectMap.get(getString(R.string.field_image_path)).toString());

                    mPhotos.add(photo);
                }
                if(count >= mFriends.size() -1){
                    //display our photos
                    displayPhotos();
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }
}

private void displayPhotos(){
    if(mPhotos != null){
        Collections.sort(mPhotos, new Comparator<Photo>() {
            @Override
            public int compare(Photo o1, Photo o2) {
                return o2.getDate_created().compareTo(o1.getDate_created());
            }
        });

        LinearLayoutManager llm = new LinearLayoutManager(getActivity());
        llm.setOrientation(LinearLayoutManager.VERTICAL);
        mRecView.setLayoutManager(llm);
        mAdapter = new ViewProfilePostsAdapter(getActivity(), mPhotos);
        mRecView.setAdapter( mAdapter );

    }
}

ViewProfilePostsAdapter.java

public class ViewProfilePostsAdapter extends RecyclerView.Adapter<ViewProfilePostsAdapter.ViewHolder> {
private static final String TAG = "CustomAdapter";

//private int[] getItemIn;

private LayoutInflater mInflater;
//private int mLayoutResource;
private Context mContext;
private DatabaseReference mReference;
private String currentUsername;

private ArrayList<Photo> list;


public static class ViewHolder extends RecyclerView.ViewHolder {
    //private final TextView textView;

    ImageView mProfileImage;
    String likesString;
    TextView username, timeDelta, caption, likes, liked;
    ImageView postImage;
    ImageView heartRed, heartWhite;

    UserAccountSettings settings = new UserAccountSettings();
    User user = new User();
    StringBuilder users;
    String mLikesString;
    boolean likeByCurrentUser;
    Heart heart;
    GestureDetector detector;
    Photo photo;

    public ViewHolder(View convertView) {
        super(convertView);
        username = (TextView) convertView.findViewById(R.id.display_name);
        postImage = (ImageView) convertView.findViewById(R.id.post_image);
        caption = (TextView) convertView.findViewById(R.id.image_caption);
        timeDelta = (TextView) convertView.findViewById(R.id.image_time_posted);
        likes = (TextView) convertView.findViewById(R.id.tvLikesString);
        mProfileImage = (ImageView) convertView.findViewById(R.id.f_profile_image);
        heartRed = (ImageView) convertView.findViewById(R.id.image_heart_red);
        heartWhite = (ImageView) convertView.findViewById(R.id.image_heart_white);
        heart = new Heart(heartWhite, heartRed);
        liked = (TextView) convertView.findViewById(R.id.likeText);
    }

}



public ViewProfilePostsAdapter(Context context, ArrayList<Photo> photo) {
    this.mContext = context;
    this.list = photo;
}

@Override
public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int viewType) {
    // Create a new view.
    LayoutInflater mInflater = (LayoutInflater) mContext.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
    View v = mInflater.inflate(R.layout.layout_post_listitem, null);

    return new ViewHolder(v);
}

@Override
public void onBindViewHolder(final ViewHolder viewHolder, final int position) {
    Log.d(TAG, "Element " + position + " set.");

    mReference = FirebaseDatabase.getInstance().getReference();


    viewHolder.photo = getItem(position);
    viewHolder.detector = new GestureDetector(mContext, new GestureListener(viewHolder));

    getCurrentUsername();

    getLikesString(viewHolder);

    viewHolder.caption.setText(getItem(position).getCaption());

    String timestampDifference = getTimestampDifference(getItem(position));
    if(!timestampDifference.equals("0")){
        viewHolder.timeDelta.setText(timestampDifference + " DAYS AGO");
    }else{
        viewHolder.timeDelta.setText("TODAY");
    }

    final ImageLoader imageLoader = ImageLoader.getInstance();
    imageLoader.displayImage(getItem(position).getImage_path(), viewHolder.postImage);


    //get the profile image and username
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    Query query = reference
            .child(mContext.getString(R.string.dbname_user_account_settings))
            .orderByChild(mContext.getString(R.string.field_user_id))
            .equalTo(getItem(position).getUser_id());
    query.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            Log.e(TAG, "onDataChange: OnDataChange ******************************************************************************");
            for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){


                Log.e(TAG, "onDataChange: found user: "
                        + singleSnapshot.getValue(UserAccountSettings.class).getUsername() + "****************************");

                viewHolder.username.setText(singleSnapshot.getValue(UserAccountSettings.class).getUsername());


                imageLoader.displayImage(singleSnapshot.getValue(UserAccountSettings.class).getProfile_photo(),
                        viewHolder.mProfileImage);

                viewHolder.settings = singleSnapshot.getValue(UserAccountSettings.class);

            }

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

    Query userQuery = mReference
            .child(mContext.getString(R.string.dbname_users))
            .orderByChild(mContext.getString(R.string.field_user_id))
            .equalTo(getItem(position).getUser_id());
    userQuery.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
                Log.d(TAG, "onDataChange: found user: " +
                        singleSnapshot.getValue(User.class).getUsername());

                viewHolder.user = singleSnapshot.getValue(User.class);
            }

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });

}

@Override
public int getItemCount() {
    return list.size();
}

public Photo getItem(int pos){
    return list.get(pos);
}



public class GestureListener extends GestureDetector.SimpleOnGestureListener{

    ViewHolder mHolder;
    public GestureListener(ViewHolder holder) {
        mHolder = holder;
    }

    @Override
    public boolean onDown(MotionEvent e) {
        return true;
    }

    @Override
    public boolean onDoubleTap(MotionEvent e) {
        Log.d(TAG, "onDoubleTap: double tap detected.");

        DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
        Query query = reference
                .child(mContext.getString(R.string.dbname_photos))
                .child(mHolder.photo.getPhoto_id())
                .child(mContext.getString(R.string.field_likes));
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){

                    String keyID = singleSnapshot.getKey();

                    //case1: Then user already liked the photo
                    if(mHolder.likeByCurrentUser &&
                            singleSnapshot.getValue(Like.class).getUser_id()
                                    .equals(FirebaseAuth.getInstance().getCurrentUser().getUid())){

                        mReference.child(mContext.getString(R.string.dbname_photos))
                                .child(mHolder.photo.getPhoto_id())
                                .child(mContext.getString(R.string.field_likes))
                                .child(keyID)
                                .removeValue();

                        mReference.child(mContext.getString(R.string.dbname_user_photos))
                                .child(mHolder.photo.getUser_id())
                                .child(mHolder.photo.getPhoto_id())
                                .child(mContext.getString(R.string.field_likes))
                                .child(keyID)
                                .removeValue();

                        mHolder.heart.toggleLike();
                        getLikesString(mHolder);
                    }
                    //case2: The user has not liked the photo
                    else if(!mHolder.likeByCurrentUser){
                        //add new like
                        addNewLike(mHolder);
                        break;
                    }
                }
                if(!dataSnapshot.exists()){
                    //add new like
                    addNewLike(mHolder);
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });

        return true;
    }
}

private void addNewLike(final ViewHolder holder){
    Log.d(TAG, "addNewLike: adding new like");

    String newLikeID = mReference.push().getKey();
    Like like = new Like();
    like.setUser_id(FirebaseAuth.getInstance().getCurrentUser().getUid());

    mReference.child(mContext.getString(R.string.dbname_photos))
            .child(holder.photo.getPhoto_id())
            .child(mContext.getString(R.string.field_likes))
            .child(newLikeID)
            .setValue(like);

    mReference.child(mContext.getString(R.string.dbname_user_photos))
            .child(holder.photo.getUser_id())
            .child(holder.photo.getPhoto_id())
            .child(mContext.getString(R.string.field_likes))
            .child(newLikeID)
            .setValue(like);

    holder.heart.toggleLike();
    getLikesString(holder);
}

private void getCurrentUsername(){
    Log.d(TAG, "getCurrentUsername: retrieving user account settings");
    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
    Query query = reference
            .child(mContext.getString(R.string.dbname_users))
            .orderByChild(mContext.getString(R.string.field_user_id))
            .equalTo(FirebaseAuth.getInstance().getCurrentUser().getUid());
    query.addListenerForSingleValueEvent(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
                currentUsername = singleSnapshot.getValue(UserAccountSettings.class).getUsername();
            }

        }

        @Override
        public void onCancelled(DatabaseError databaseError) {

        }
    });
}

private void getLikesString(final ViewHolder holder){
    Log.d(TAG, "getLikesString: getting likes string");

    try{
        DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
        Query query = reference
                .child(mContext.getString(R.string.dbname_photos))
                .child(holder.photo.getPhoto_id())
                .child(mContext.getString(R.string.field_likes));
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(DataSnapshot dataSnapshot) {
                holder.users = new StringBuilder();
                for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){

                    DatabaseReference reference = FirebaseDatabase.getInstance().getReference();
                    Query query = reference
                            .child(mContext.getString(R.string.dbname_users))
                            .orderByChild(mContext.getString(R.string.field_user_id))
                            .equalTo(singleSnapshot.getValue(Like.class).getUser_id());
                    query.addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(DataSnapshot dataSnapshot) {
                            for(DataSnapshot singleSnapshot : dataSnapshot.getChildren()){
                                Log.d(TAG, "onDataChange: found like: " +
                                        singleSnapshot.getValue(User.class).getUsername());

                                holder.users.append(singleSnapshot.getValue(User.class).getUsername());
                                holder.users.append(",");
                            }

                            String[] splitUsers = holder.users.toString().split(",");

                            if(holder.users.toString().contains(currentUsername + ",")){//mitch, mitchell.tabian
                                holder.likeByCurrentUser = true;
                            }else{
                                holder.likeByCurrentUser = false;
                            }

                            int length = splitUsers.length;
                            if(length == 1){
                                holder.likesString = "Liked by " + splitUsers[0];
                            }
                            else if(length == 2){
                                holder.likesString = "Liked by " + splitUsers[0]
                                        + " and " + splitUsers[1];
                            }
                            else if(length == 3){
                                holder.likesString = "Liked by " + splitUsers[0]
                                        + ", " + splitUsers[1]
                                        + " and " + splitUsers[2];

                            }
                            else if(length == 4){
                                holder.likesString = "Liked by " + splitUsers[0]
                                        + ", " + splitUsers[1]
                                        + ", " + splitUsers[2]
                                        + " and " + splitUsers[3];
                            }
                            else if(length > 4){
                                holder.likesString = "Liked by " + splitUsers[0]
                                        + ", " + splitUsers[1]
                                        + ", " + splitUsers[2]
                                        + " and " + (splitUsers.length - 3) + " others";
                            }
                            Log.d(TAG, "onDataChange: likes string: " + holder.likesString);
                            //setup likes string
                            setupLikesString(holder, holder.likesString);
                        }

                        @Override
                        public void onCancelled(DatabaseError databaseError) {

                        }
                    });
                }
                if(!dataSnapshot.exists()){
                    holder.likesString = "";
                    holder.likeByCurrentUser = false;
                    //setup likes string
                    setupLikesString(holder, holder.likesString);
                }
            }

            @Override
            public void onCancelled(DatabaseError databaseError) {

            }
        });
    }catch (NullPointerException e){
        Log.e(TAG, "getLikesString: NullPointerException: " + e.getMessage() );
        holder.likesString = "";
        holder.likeByCurrentUser = false;
        //setup likes string
        setupLikesString(holder, holder.likesString);
    }
}

private void setupLikesString(final ViewHolder holder, String likesString) {
    Log.d(TAG, "setupLikesString: likes string:" + holder.likesString);

    if (holder.likeByCurrentUser) {
        Log.d(TAG, "setupLikesString: photo is liked by current user");
        holder.liked.setText("UnLike");
        holder.heartWhite.setVisibility(View.GONE);
        holder.heartRed.setVisibility(View.VISIBLE);
        holder.heartRed.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                return holder.detector.onTouchEvent(event);
            }
        });
    } else {
        Log.d(TAG, "setupLikesString: photo is not liked by current user");
        holder.liked.setText("Like");
        holder.heartWhite.setVisibility(View.VISIBLE);
        holder.heartRed.setVisibility(View.GONE);
        holder.heartWhite.setOnTouchListener(new View.OnTouchListener() {
            @Override
            public boolean onTouch(View v, MotionEvent event) {
                return holder.detector.onTouchEvent(event);
            }
        });
    }
    holder.likes.setText(likesString);

}


//---------------------------------------------end of likes----------------------------

private String getTimestampDifference(Photo photo){
    Log.d(TAG, "getTimestampDifference: getting timestamp difference.");

    String difference = "";
    Calendar c = Calendar.getInstance();
    SimpleDateFormat sdf = new SimpleDateFormat("yyyy-MM-dd'T'HH:mm:ss'Z'", Locale.CANADA);
    sdf.setTimeZone(TimeZone.getTimeZone("Canada/Pacific"));//google 'android list of timezones'
    Date today = c.getTime();
    sdf.format(today);
    Date timestamp;
    final String photoTimestamp = photo.getDate_created();
    try{
        timestamp = sdf.parse(photoTimestamp);
        difference = String.valueOf(Math.round(((today.getTime() - timestamp.getTime()) / 1000 / 60 / 60 / 24 )));
    }catch (ParseException e){
        Log.e(TAG, "getTimestampDifference: ParseException: " + e.getMessage() );
        difference = "0";
    }
    return difference;
}

Answer 1

尝试在onCreateView()中设置一个空适配器，并在想要更新数据时调用adapter.notifyDataSetChanged。

因此，在调用 getFriends() 之前的 onCreateView() 方法中，您应该初始化适配器并将其设置为回收器 View

public View onCreateView(LayoutInflater inflater, @Nullable ViewGroup container, @Nullable Bundle savedInstanceState) {
    View view = inflater.inflate(R.layout.fragment_profile_posts, container, false);
    mRecView = (RecyclerView) view.findViewById(R.id.lvProfilePosts);
    mFriends = new ArrayList<>();
    mPhotos = new ArrayList<>();

    mAdapter = new ViewProfilePostsAdapter(getActivity(), mPhotos);
    mRecView.setAdapter(mAdapter);
    getFriends();


    return view;
}

并在你的displayPhotos()中调用mAdapter.notifyDataSetChanged();

    private void displayPhotos(){
    if(mPhotos != null){
        Collections.sort(mPhotos, new Comparator<Photo>() {
            @Override
            public int compare(Photo o1, Photo o2) {
                return o2.getDate_created().compareTo(o1.getDate_created());
            }
        });

        LinearLayoutManager llm = new LinearLayoutManager(getActivity());
        llm.setOrientation(LinearLayoutManager.VERTICAL);
        mRecView.setLayoutManager(llm);
        mAdapter.notifyDataSetChanged();

    }
}