Question

我在使用回收站视图在android中实现无限滚动时遇到问题。我想要的是，基本上，像instagram一样，你无休止地滚动页面。

我有一个包含10个项目的Firebase数据库，我想要显示3个项目并为接下来的两个项目充电，然后当您滚动下两个项目时开始加载下一个项目，依此类推。（您将看到示例中的大部分内容都是硬编码的。）

我无法像这样制作Firebase查询：

myRef.orderByChild("id").startAt(page*5 + "").endAt(5+page*5 + "")

我想要获得的是在我当前位置接下来的5个项目和id之间 - 让我们说 - 5和10.但是，当我这样做时：

    myRef.orderByChild("id").startAt(page*5 + "").endAt(5+page*5 + "")
            .getRef().addValueEventListener(new ValueEventListener() {
        @Override
        public void onDataChange(DataSnapshot dataSnapshot) {
            int i = 0;
            for (DataSnapshot postSnapshot : dataSnapshot.getChildren()) {
                if(i == 5) break;
                mDataset.add(postSnapshot.getValue(Card.class));
                i++;
            }

            mAdapter = new CustomAdapter(mDataset);
            mRecyclerView.setAdapter(mAdapter);
        }

        @Override
        public void onCancelled(DatabaseError databaseError) {
        }
    });

所有postSnapshots都会返回ID 1,2,3,4,5。这样可以无休止地滚动，但每次都会收取相同的5个项目。

由于

编辑：

EndlessScrollListener

public abstract class EndlessScrollListener extends RecyclerView.OnScrollListener {
    private int mVisibleThreshold = 2,
            mCurrentPage = 0,
            mPreviousTotalItemCount = 0,
            mStartingPageIndex = 0;

    private boolean mLoading = true;

    RecyclerView.LayoutManager mLayoutManager;

    public EndlessScrollListener(){}

    public EndlessScrollListener(LinearLayoutManager layoutManager){
        mLayoutManager = layoutManager;
    }

    public EndlessScrollListener(int visibleThreshold){
        mVisibleThreshold = visibleThreshold;
    }

    public int getLastVisibleItem(int[] lastVisibleItemPositions){
        int maxSize = lastVisibleItemPositions[0];
        for(int i = 1; i < lastVisibleItemPositions.length; ++i){
            if(lastVisibleItemPositions[i] > maxSize)
                maxSize = lastVisibleItemPositions[i];
        }
        return maxSize;
    }

    @Override
    public void onScrolled(RecyclerView view, int dx, int dy){
        int lastVisibleItemPosition = 0,
                totalItemCount = mLayoutManager.getItemCount();

        if (mLayoutManager instanceof LinearLayoutManager) {
            lastVisibleItemPosition =
                    ((LinearLayoutManager) mLayoutManager).findLastVisibleItemPosition();
        }

        if(totalItemCount < mPreviousTotalItemCount){
            mCurrentPage = mStartingPageIndex;
            mPreviousTotalItemCount = totalItemCount;
            mLoading = totalItemCount == 0;
        }

        if(mLoading && totalItemCount > mPreviousTotalItemCount){
            mLoading = false;
            mPreviousTotalItemCount = totalItemCount;
        }

        if(!mLoading && (lastVisibleItemPosition + mVisibleThreshold) > totalItemCount){
            mCurrentPage++;
            onLoadMore(mCurrentPage, totalItemCount, view);
            mLoading = true;
        }
    }

    public abstract void onLoadMore(int page, int totalItemsCount, RecyclerView view);

    public void resetState(){
        mCurrentPage = mStartingPageIndex;
        mPreviousTotalItemCount = 0;
        mLoading = true;
    }
}

在其活动中

scrollListener = new EndlessScrollListener(mLayoutManager) {
        @Override
        public void onLoadMore(int page, int totalItemsCount, RecyclerView view) {
            System.out.println("Dale... Page: " + page + " items: " + totalItemsCount);

            loadData(page);
        }
    };

无法进行Firebase查询

0 个答案: