Question

我需要知道如何在使用Firebase滚动时动态加载数据。我想从Firebase获得最高限额50的记录。达到此限制后，我将下载下50个数据。

MarkerActivity.java

public class MarkerActivity extends AppCompatActivity implements NavigationView.OnNavigationItemSelectedListener{


    private LinearLayoutManager layoutManager;
    private ViewSwitcher mViewSwitcher;
    private MarkerAdapter mMarkerAdapter;
    private RecyclerView recyclerView
    private int page_number = 1;
    private int item_count = 10;
    private boolean isLoading = true;
    private int pastVisibleItems, visibleItemCount,totallItemCount,previous_totall = 0;
    private int view_threshold = 10;

    @Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_markers);
        recyclerView = findViewById(R.id.recycler_view);
        layoutManager = new LinearLayoutManager(this);
        recyclerView.setHasFixedSize(true);
        recyclerView.setLayoutManager(layoutManager);
        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                visibleItemCount = layoutManager.getChildCount();
                totallItemCount = layoutManager.getItemCount();
                pastVisibleItems = layoutManager.findLastVisibleItemPosition();

                if (dy>0)
                {
                    if (isLoading)
                    {
                        if (totallItemCount>previous_totall)
                        {
                            isLoading = false;
                            previous_totall = totallItemCount;
                        }
                    }

                    if (!isLoading&&(totallItemCount-visibleItemCount)<=(pastVisibleItems=view_threshold))
                    {
                        page_number++;
                        isLoading = true;
                    }}
        });
    }
}

你能帮帮我吗？

Answer 1

使用以下代码，您可以在firebase中实现分页：设置firebase限制查询：

Query first = db.collection("cities")
        .orderBy("population")
        .limit(25);

first.get()
    .addOnSuccessListener(new OnSuccessListener<QuerySnapshot>() {
        @Override
        public void onSuccess(QuerySnapshot documentSnapshots) {
            // ...

            // Get the last visible document
            DocumentSnapshot lastVisible = documentSnapshots.getDocuments()
                    .get(documentSnapshots.size() -1);

            // Construct a new query starting at this document,
            // get the next 25 cities.
            Query next = db.collection("cities")
                    .orderBy("population")
                    .startAfter(lastVisible)
                    .limit(25);

            // Use the query for pagination
            // ...
        }
    });

要获得更多知识，您需要查看链接： Check this link for pagination in firebase

Answer 2

 Query query = mDatabaseReference.orderByKey().limitToLast(50);
        query.addListenerForSingleValueEvent(new ValueEventListener() {
            @Override
            public void onDataChange(@NonNull DataSnapshot dataSnapshot) {

                boolean isFirst = true;
                for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                    if (isFirst) {
                        isFirst = false;
                        oldPostId = postSnapshot.getKey();
                    }
                    Post post = postSnapshot.getValue(Post.class);
                    if (post != null)
                        mPostRecyclerAdapter.addPost(new Post(post.getUserName(), post.getPost(), post.getPostOwnerUuid(), postSnapshot.getKey(), post.getTotalLikes(), post.getPostTime(), post.getCategoryName()));
                }
               //set your adapter here after adding item to recycler view

            }

现在使用recyclerview的OnscrollListener。

mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
                super.onScrollStateChanged(recyclerView, newState);
                if (newState == AbsListView.OnScrollListener.SCROLL_STATE_TOUCH_SCROLL) {
                    isScrolling = true;
                }
            }

            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                currentVisibleItem = linearLayoutManager.getChildCount();
                totalItem = linearLayoutManager.getItemCount();
                scrolledItem = linearLayoutManager.findFirstVisibleItemPosition();
                if (isScrolling && (currentVisibleItem + scrolledItem == totalItem) && !isEndChildResults && oldPostId != null) {
                    scrollCount++;
                    showInterstitial(scrollCount);
                    isScrolling = false;
                    mProgressBarScroll.setVisibility(View.VISIBLE);
                    Query query = mDatabaseReference.orderByKey().endAt(oldPostId).limitToLast(50);
                    query.addListenerForSingleValueEvent(new ValueEventListener() {
                        @Override
                        public void onDataChange(@NonNull DataSnapshot dataSnapshot) {
                            int count = 0;

                            mPostRecyclerAdapter.clearReversePostList();
                            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                                count++;
                                if (dataSnapshot.getChildrenCount() < 50) {
                                    isEndChildResults = true;
                                } else {
                                    if (count == 1) {
                                        oldPostId = postSnapshot.getKey();
                                    }
                                }
                                if (count != 50) {
                                    Post post = postSnapshot.getValue(Post.class);
                                    if (post != null)
                                        mPostRecyclerAdapter.addPost(new Post(post.getUserName(), post.getPost(), post.getPostOwnerUuid(), postSnapshot.getKey(), post.getTotalLikes(), post.getPostTime(), post.getCategoryName()));
                                    mPostRecyclerAdapter.notifyDataSetChanged();
                                }
                            }

                        }

                        @Override
                        public void onCancelled(@NonNull DatabaseError databaseError) {

                        }
                    });
                }
                if (isEndChildResults && (firstVisibleItem < scrolledItem) && !isSnackBarShown) {
                    snackbar = Snackbar.make(coordinatorLayout, R.string.no_more_post_available, Snackbar.LENGTH_INDEFINITE)
                            .setAction(getString(R.string.ok), new View.OnClickListener() {
                                @Override
                                public void onClick(View view) {
                                    snackbar.dismiss();
                                }
                            });
                    snackbar.show();
                    isSnackBarShown = true;
                }
            }
        });

Answer 3

这是从我身边完成的。你可以试试这个。

像这样添加监听器赞：

Query newItems = FirebaseDatabase.getInstance().getReference();
        newItems.getRef().child(“Child")
                         .child(“Child")
                         .getRef().orderByChild(Constants.ARG_CONV_TIMESTEMP)
                         .limitToLast(10).addChildEventListener(childEventListener);

观察员：

private ChildEventListener childEventListener = new ChildEventListener() {
    @Override
    public void onChildAdded(DataSnapshot dataSnapshot, String s) {
        ChatBean chat = dataSnapshot.getValue(ChatBean.class);
    }


    @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(DatabaseError databaseError) {

    }
};

删除侦听器，如：

newItems.getRef().child(“Child")
                         .child(“Child")
                         .getRef().removeEventListener(childEventListener);

Firebase数据库分页

3 个答案: