onScrolled 在没有用户滚动的情况下被调用（Recycler View 无限滚动）

Question

尝试了所有相关的问题，但没有奏效:(

我正在使用 Recycler View 构建无限滚动。

问题： onScrolled 方法总是在用户不滚动屏幕的情况下被调用。

Android 文档指南对 onScrolled 方法进行了描述：

Case 1) RecyclerView 被调用的回调方法 滚动。这将在滚动完成后调用。

案例 2) 如果可见项目范围发生变化，也会调用此回调 经过布局计算。在这种情况下，dx 和 dy 将为 0。

由于案例 2，我的 onScrolled 方法在没有用户滚动的情况下被调用。我在屏幕上记录了 dy，结果发现 onScrolled 是用 dy=0 调用的。这发生在第二种情况下。

如果我使用：

if (dy > 0){
    // The user is scrolling down
}

事实证明，无论我滚动 Recycler 视图多少次，我的 onScrolled 方法都不会被调用。

我的代码

RecyclerAdapterSmallVideos.java

public class  RecyclerAdapterSmallVideos extends RecyclerView.Adapter<RecyclerView.ViewHolder> {

    private List<VideosBigSize> videosBigSizeList;
    private Context mContext;

    final int VIEW_TYPE_ITEM = 0, VIEW_TYPE_LOADING = 1;
    ILoadMore loadMore;
    boolean isLoading;
    int visibleThreshold = 5;
    int lastVisibleItem, totalItemCount;

    public RecyclerAdapterSmallVideos(RecyclerView recyclerView, Context context, List<VideosBigSize> videosBigSizeList) {
        this.videosBigSizeList = videosBigSizeList;
        this.mContext = context;

        final LinearLayoutManager linearLayoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();
        recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);

                totalItemCount = linearLayoutManager.getItemCount();
                lastVisibleItem = linearLayoutManager.findLastVisibleItemPosition();
                if (!isLoading && totalItemCount <= (lastVisibleItem + visibleThreshold)) {

                    if (loadMore != null) {

                        // This is running without the user scrolling the Recycler View. 
                        loadMore.onLoadMore();
                    }
                    isLoading = true;

                }

            }
        });


    }


    @Override
    public int getItemViewType(int position) {
        return videosBigSizeList.get(position) == null ? VIEW_TYPE_LOADING: VIEW_TYPE_ITEM;
    }


    public void setLoadMore(ILoadMore loadMore) {
        this.loadMore = loadMore;
    }

    @NonNull
    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(@NonNull ViewGroup parent, int viewType) {

        if (viewType == VIEW_TYPE_ITEM) {

            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_small_video, parent, false);
            return new ViewHolderSmallVideos(view);
        } else if (viewType == VIEW_TYPE_LOADING) {

            View view = LayoutInflater.from(parent.getContext()).inflate(R.layout.item_loading, parent, false);
            return new ViewHolderLoading(view);
        }
        return null;
    }


    @Override
    public void onBindViewHolder(@NonNull final RecyclerView.ViewHolder holder, final int position) {

        /*########### Case 1) The holder is a instance off ViewHolderSmallVideos (Items) ###########*/
        if (holder instanceof ViewHolderSmallVideos) {

            Log.i("Debugging", "onBindViewHolder: Binding instance of ViewHolder SmallVideos: " + holder.getAdapterPosition());

            VideosBigSize singleVideoBigSize = videosBigSizeList.get(position);

            ViewHolderSmallVideos viewHolderSmallVideos = (ViewHolderSmallVideos) holder;

            // Step 1) Images
            GlideApp.with(viewHolderSmallVideos.thumbNail.getContext())
                    .load(singleVideoBigSize.getThumnail_url())
                    .centerCrop()
                    .into(viewHolderSmallVideos.thumbNail); // Video Thumbnail

            // Step 2) Determine the Max Length for each TextView
            setTextMaxLength(viewHolderSmallVideos.videoTitle, viewHolderSmallVideos.channelName, mContext);

            // Step 3) Texts
            viewHolderSmallVideos.videoTitle.setText(singleVideoBigSize.getVideo_title());
            viewHolderSmallVideos.channelName.setText(singleVideoBigSize.getChannel_name());
            viewHolderSmallVideos.videoViews.setText(singleVideoBigSize.getVideo_views());
            viewHolderSmallVideos.videoUploadDate.setText(singleVideoBigSize.getVideo_upload_date());
            viewHolderSmallVideos.videoDuration.setText(singleVideoBigSize.getVideo_duration());

            // Step 4) Handle clicks
            viewHolderSmallVideos.constraintLayoutEachItem.setOnClickListener(new View.OnClickListener() {
                @Override
                public void onClick(View v) {
                    Toast.makeText(mContext, String.valueOf(holder.getAdapterPosition()), Toast.LENGTH_SHORT).show();
                }
            });
        }

        /*########### Case 2) The holder is a instance off ViewHolderLoading (progressBar) ###########*/
        else if (holder instanceof ViewHolderLoading) {

            Log.i("Debugging", "onBindViewHolder: Binding instance of ViewHolder Loading: " + holder.getAdapterPosition());

            ViewHolderLoading viewHolderLoading = (ViewHolderLoading) holder;
            viewHolderLoading.progressBar.setIndeterminate(true);

        }

    }

    /**
     * Get the number of items in the adapter
     * @return the number of items in the adapter
     */
    @Override
    public int getItemCount() { return videosBigSizeList.size(); }


    public void setLoaded() {
        isLoading = false;
    }

    /**
     * Determine a maximum number of characters for the Title and Channel Name
     * If they are too big and the width of the screen is too small, the text
     * will get bigger than the thumbnail and then the layout will be disturbed.
     * @param videoTitle the title of the video
     * @param channelName the name of the channel who uploaded the video
     * @param context the activity context
     */
    private void setTextMaxLength(TextView videoTitle, TextView channelName, Context context) {

        DisplayMetrics displayMetrics = new DisplayMetrics();
        WindowManager windowManager = (WindowManager) context.getSystemService(Context.WINDOW_SERVICE);

        if (windowManager != null) {

            // Get the current width of the screen in DP
            windowManager.getDefaultDisplay().getMetrics(displayMetrics);
            float dpWidth = displayMetrics.widthPixels / displayMetrics.density;

            // 1) If the device is 420dp or less;
            // 2) Limit the number of characters for the title and channel name
            if (dpWidth <= 420) {
                videoTitle.setFilters(new InputFilter[]{new InputFilter.LengthFilter(35)});
                channelName.setFilters(new InputFilter[]{new InputFilter.LengthFilter(25)});
            }
        }

    }

}

ProfileFragment.java

private void setupRecyclerView(final List<VideosBigSize> userAllVideosList) {

        LinearLayoutManager linearLayoutManager = new LinearLayoutManager(mContext);
        mRecyclerView.setLayoutManager(linearLayoutManager);
        mRecyclerView.setNestedScrollingEnabled(false);
        final RecyclerAdapterSmallVideos adapterSmallVideos = new RecyclerAdapterSmallVideos(mRecyclerView, mContext, userAllVideosList);
        mRecyclerView.setAdapter(adapterSmallVideos);

        // Set Load more event
        adapterSmallVideos.setLoadMore(new ILoadMore() {
            @Override
            public void onLoadMore() {
                if (userAllVideosList.size() <= 50) {
                    mRecyclerView.post(new Runnable() {
                        @Override
                        public void run() {
                            userAllVideosList.add(null); 
                            adapterSmallVideos.notifyItemInserted(userAllVideosList.size() - 1);

                        }
                    });
                    new Handler().postDelayed(new Runnable() {
                        @Override
                        public void run() {
                            userAllVideosList.remove(userAllVideosList.size() - 1);
                            adapterSmallVideos.notifyItemRemoved(userAllVideosList.size()); 

                            // Random more data
                            int index = userAllVideosList.size();
                            int end = index + 10;
                            for (int i = index; i < end; i++) {
                                // Add more data to userAllVideosList...
                                adapterSmallVideos.notifyItemInserted(i);

                            }

                            adapterSmallVideos.setLoaded();

                        }
                    }, 2000);
                }
                // Loaded everything already
                else {
                    Toast.makeText(mContext, "Load data completed!", Toast.LENGTH_SHORT).show();
                }
            }
        });

    }

我的 ProfileFragment 布局

fragment_profile.xml

请务必注意：

1) 我的 Recycler 视图位于 NesteScrollView 内，因为我需要隐藏/显示工具栏。记得我设置了 mRecyclerView.setNestedScrollingEnabled(false) 因为它触发了 NestedScrollView；

2) 除了回收站视图之外，我的布局中还有更多内容。

Answer 1

你应该使用分页库来做到这一点，click to see the best tutorial：

And the Github source code of the tutorial

事实证明，因为分页库是一项新功能，所以我只找到了 Kotlin 教程。然后我发现这可能是用 Java 编写的最好的一个。真的感谢作者，我为此苦苦挣扎了整整一个月。