java - 如何在 RecyclerView 中实现 setOnScrollListener

Question

当用户到达列表中可见的项目时，如何在底部显示进度条。

我编写了一段代码，我在其中使用 Web 服务获取数据，现在我想填充部分记录，因为我的 JSON 中有大约 630 条记录。

这是我用来从 JSON 获取数据并填充到 RecyclerView 中的整个代码。

这是我的 JSON 的样子，但真正的 JSON 包含超过 600 条记录:

 http://walldroidhd.com/api.php

有人可以指导我在哪里更改我的代码吗？

每当用户使用进度条滚动到底部时，我想填充更多记录，但我仍然显示所有记录。

RecyclerViewFragment.java:

public class RecyclerViewFragment extends Fragment {

    RecyclerView mRecyclerView;
    LinearLayoutManager mLayoutManager;
    RecyclerView.Adapter mAdapter;
    ArrayList<NatureItem> actorsList;

    private int previousTotal = 0;
    private boolean loading = true;
    private int visibleThreshold = 5;
    int firstVisibleItem, visibleItemCount, totalItemCount;

    public static RecyclerViewFragment newInstance() {
        return new RecyclerViewFragment();
    }

    @Override
    public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
        return inflater.inflate(R.layout.fragment_recyclerview_advance, container, false);
    }

    @Override
    public void onViewCreated(View view, Bundle savedInstanceState) {
        super.onViewCreated(view, savedInstanceState);

        actorsList = new ArrayList<NatureItem>();

        new JSONAsyncTask().execute("my JSON url");

        mRecyclerView = (RecyclerView) view.findViewById(R.id.recycler_view);
        mRecyclerView.setHasFixedSize(true);

        mLayoutManager = new GridLayoutManager(getActivity(), 2);
        mRecyclerView.setLayoutManager(mLayoutManager);

        mRecyclerView.setOnScrollListener(new RecyclerView.OnScrollListener() {

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

                visibleItemCount = mRecyclerView.getChildCount();
                totalItemCount = mLayoutManager.getItemCount();
                firstVisibleItem = mLayoutManager.findFirstVisibleItemPosition();

                if (loading) {
                    if (totalItemCount > previousTotal) {
                        loading = false;
                        previousTotal = totalItemCount;
                    }
                }
                if (!loading && (totalItemCount - visibleItemCount)
                        <= (firstVisibleItem + visibleThreshold)) {
                    // End has been reached

                    Log.i("...", "end called");

                    // Do something

                    loading = true;
                }
            }
        });

        // mAdapter = new CardAdapter();
        mAdapter = new RecyclerViewMaterialAdapter(new CardAdapter(getActivity(), actorsList), 2);
        mRecyclerView.setAdapter(mAdapter);

        MaterialViewPagerHelper.registerRecyclerView(getActivity(), mRecyclerView, null);

        mRecyclerView.addOnItemTouchListener(
                new RecyclerItemClickListener(getActivity(), new RecyclerItemClickListener.OnItemClickListener() {
                    @Override
                    public void onItemClick(View view, int position) {

                        Toast.makeText(getActivity(), String.valueOf(position), Toast.LENGTH_LONG).show();

                    }
                })
        );

    }

    class JSONAsyncTask extends AsyncTask<String, Void, Boolean> {

        ProgressDialog dialog;

        @Override
        protected void onPreExecute() {
            super.onPreExecute();
            dialog = new ProgressDialog(getActivity());
            dialog.setMessage("Loading, please wait");
            dialog.setTitle("Connecting server");
            dialog.show();
            dialog.setCancelable(false);
        }

        @Override
        protected Boolean doInBackground(String... urls) {
            try {

                //------------------>>
                HttpGet httppost = new HttpGet(urls[0]);
                HttpClient httpclient = new DefaultHttpClient();
                HttpResponse response = httpclient.execute(httppost);

                // StatusLine stat = response.getStatusLine();
                int status = response.getStatusLine().getStatusCode();

                if (status == 200) {
                    HttpEntity entity = response.getEntity();
                    String data = null;
                    try {
                        data = EntityUtils.toString(entity);
                    } catch (IOException e) {
                        e.printStackTrace();
                    }


                    JSONObject jsono = null;
                    try {
                        jsono = new JSONObject(data);
                    } catch (JSONException e) {
                        e.printStackTrace();
                    }
                    JSONArray jarray = jsono.getJSONArray("wallpapers");


                    for (int i = 0; i < jarray.length(); i++) {
                        JSONObject object = jarray.getJSONObject(i);

                        NatureItem actor = new NatureItem();

                        actor.setName(object.getString("id"));
                        actor.setThumbnail(object.getString("thumb_url"));

                        actorsList.add(actor);
                    }
                    return true;
                }

                //------------------>>

            } catch (ParseException e1) {
                e1.printStackTrace();
            } catch (IOException e) {
                e.printStackTrace();
            } catch (JSONException e) {
                e.printStackTrace();
            }
            return false;
        }

        protected void onPostExecute(Boolean result) {
            dialog.cancel();
            mAdapter.notifyDataSetChanged();
            if (result == false) {
                Toast.makeText(getActivity(), "Unable to fetch data from server", Toast.LENGTH_LONG).show();
            }
            else {

            }

        }
    }
}

CardAdapter.java:

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

    private ArrayList<NatureItem> mItems;
    private Context mContext;

    public CardAdapter(Context context, ArrayList<NatureItem> feedItemList) {
        this.mItems = feedItemList;
        this.mContext = context;
    }

    @Override
    public ViewHolder onCreateViewHolder(ViewGroup viewGroup, int i) {
        View v = LayoutInflater.from(viewGroup.getContext())
                .inflate(R.layout.recycler_view_card_item, viewGroup, false);

        ViewHolder viewHolder = new ViewHolder(v);
        return viewHolder;
    }

    @Override
    public void onBindViewHolder(ViewHolder viewHolder, int i) {
        NatureItem nature = mItems.get(i);
        viewHolder.tvNature.setText(nature.getName());

        Picasso.with(mContext).load(nature.getThumbnail())
                .error(R.mipmap.ic_launcher)
                .placeholder(R.mipmap.ic_launcher)
                .into(viewHolder.imgThumbnail);

    }

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

    class ViewHolder extends RecyclerView.ViewHolder{

        public ImageView imgThumbnail;
        public TextView tvNature;

        public ViewHolder(View itemView) {
            super(itemView);
            imgThumbnail = (ImageView)itemView.findViewById(R.id.img_thumbnail);
            tvNature = (TextView)itemView.findViewById(R.id.tv_nature);
        }
    }
}

这也是我使用 this 实现 Endless 的方法:

mRecyclerView.setOnScrollListener(new EndlessRecyclerOnScrollListener(linearLayoutManager) {
            @Override
            public void onLoadMore(int current_page) {
                // do something...
            }
        });

注意:我个人更喜欢 RecyclerView onScroll 功能来完成我的工作。

Answer 1

xml布局文件中带有recyclerview的Activity类

public class WallpaperActivity extends AppCompatActivity implements OnTaskCompleted {


private static final String TAG = "WallpaperActivity";


private Toolbar toolbar;


private RecyclerView mRecyclerView;
private WallPaperDataAdapter mAdapter;
private LinearLayoutManager mLayoutManager;
// to keep track which pages loaded and next pages to load
public static int pageNumber;

private List<WallPaper> wallpaperImagesList;


protected Handler handler;

@Override
protected void onCreate(Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setContentView(R.layout.wallpaper_main);
    toolbar = (Toolbar) findViewById(R.id.toolbar);
    mRecyclerView = (RecyclerView) findViewById(R.id.my_recycler_view);
    pageNumber = 1;
    wallpaperImagesList = new ArrayList<WallPaper>();
    handler = new Handler();
    if (toolbar != null) {
        setSupportActionBar(toolbar);
        getSupportActionBar().setTitle("WallPapers");

    }


    // use this setting to improve performance if you know that changes
    // in content do not change the layout size of the RecyclerView
    mRecyclerView.setHasFixedSize(true);


    mLayoutManager = new LinearLayoutManager(this);


    // use a linear layout manager
    mRecyclerView.setLayoutManager(mLayoutManager);


    // create an Object for Adapter
    mAdapter = new WallPaperDataAdapter(wallpaperImagesList, mRecyclerView);

    // set the adapter object to the Recyclerview
    mRecyclerView.setAdapter(mAdapter);


    getWebServiceData();


    mAdapter.setOnLoadMoreListener(new OnLoadMoreListener() {
        @Override
        public void onLoadMore() {
            //add null , so the adapter will check view_type and show progress bar at bottom
            wallpaperImagesList.add(null);
            mAdapter.notifyItemInserted(wallpaperImagesList.size() - 1);
            ++pageNumber;


            getWebServiceData();


        }
    });


}


public void getWebServiceData() {

    BackGroundTask backGroundTask = new BackGroundTask(this, this, pageNumber);
    backGroundTask.execute();

}


@Override
public void onTaskCompleted(String response) {


    parsejosnData(response);

}


public void parsejosnData(String response) {

    try {

        JSONObject jsonObject = new JSONObject(response);

        //    String json = jsonObject.toString();

        JSONArray jsonArray = jsonObject.getJSONArray("wallpapers");


        if (jsonArray != null) {
            // looping through All albums


            if (pageNumber > 1) {
                wallpaperImagesList.remove(wallpaperImagesList.size() - 1);
                mAdapter.notifyItemRemoved(wallpaperImagesList.size());
            }

            for (int i = 0; i < jsonArray.length(); i++) {
                JSONObject c = jsonArray.getJSONObject(i);

                // Storing each json item values in variable
                String id = c.getString("id");
                String orig_url = c.getString("orig_url");
                String thumb_url = c.getString("thumb_url");
                String downloads = c.getString("downloads");
                String fav = c.getString("fav");

                // Creating object for each product
                WallPaper singleWall = new WallPaper(id, orig_url, thumb_url, downloads, fav);

                // adding HashList to ArrayList
                wallpaperImagesList.add(singleWall);


                handler.post(new Runnable() {
                    @Override
                    public void run() {
                       mAdapter.notifyItemInserted(wallpaperImagesList.size());


                    }
                });


            }


            mAdapter.setLoaded();


        } else {
            Log.d("Wallpapers: ", "null");
        }

    } catch (JSONException e) {
        e.printStackTrace();
    }

}


}

适配器类

public class WallPaperDataAdapter extends RecyclerView.Adapter {
    private final int VIEW_ITEM = 1;
    private final int VIEW_PROG = 0;

    private List<WallPaper> imagesList;

    // The minimum amount of items to have below your current scroll position
    // before loading more.
    private int visibleThreshold = 5;
    private int lastVisibleItem, totalItemCount;
    private boolean loading;
    private OnLoadMoreListener onLoadMoreListener;


    public WallPaperDataAdapter(List<WallPaper> imagesList1, RecyclerView recyclerView) {
        imagesList = imagesList1;

        if (recyclerView.getLayoutManager() instanceof LinearLayoutManager) {

            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 (!loading
                                    && totalItemCount <= (lastVisibleItem + visibleThreshold)) {
                                // End has been reached
                                // Do something
                                if (onLoadMoreListener != null) {
                                    onLoadMoreListener.onLoadMore();
                                }
                                loading = true;
                            }
                        }
                    });
        }
    }

    @Override
    public int getItemViewType(int position) {
        return imagesList.get(position) != null ? VIEW_ITEM : VIEW_PROG;
    }

    @Override
    public RecyclerView.ViewHolder onCreateViewHolder(ViewGroup parent,
                                                      int viewType) {
        RecyclerView.ViewHolder vh;
        if (viewType == VIEW_ITEM) {
            View v = LayoutInflater.from(parent.getContext()).inflate(
                    R.layout.wallpaper_row, parent, false);

            vh = new WallPaperViewHolder(v);
        } else {
            View v = LayoutInflater.from(parent.getContext()).inflate(
                    R.layout.progress_item, parent, false);

            vh = new ProgressViewHolder(v);
        }
        return vh;
    }

    @Override
    public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
        if (holder instanceof WallPaperViewHolder) {

            WallPaper singleWallPaper = (WallPaper) imagesList.get(position);


            Glide.with(((WallPaperViewHolder) holder).thumbIcon.getContext())
                    .load(singleWallPaper.getThumbUrl())
                    .centerCrop()
                    .placeholder(R.drawable.bg)
                    .crossFade()
                    .into(((WallPaperViewHolder) holder).thumbIcon);


        } else {
            ((ProgressViewHolder) holder).progressBar.setIndeterminate(true);
        }
    }

    public void setLoaded() {
        loading = false;
    }

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

    public void setOnLoadMoreListener(OnLoadMoreListener onLoadMoreListener) {
        this.onLoadMoreListener = onLoadMoreListener;
    }


    //
    public static class WallPaperViewHolder extends RecyclerView.ViewHolder {


        public ImageView thumbIcon;


        public WallPaperViewHolder(View v) {
            super(v);


            thumbIcon = (ImageView) v.findViewById(R.id.thumbIcon);


        }
    }

    public static class ProgressViewHolder extends RecyclerView.ViewHolder {
        public ProgressBar progressBar;

        public ProgressViewHolder(View v) {
            super(v);
            progressBar = (ProgressBar) v.findViewById(R.id.progressBar1);
        }
    }
}

wallpaper_row.xml

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content">

<ImageView
    android:id="@+id/thumbIcon"
    android:layout_width="160dp"
    android:layout_height="160dp"
    android:layout_centerInParent="true"
    android:layout_margin="2dp"
    android:gravity="center" />

</RelativeLayout>

progress_item.xml

<?xml version="1.0" encoding="utf-8"?>
<LinearLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:layout_width="match_parent"
    android:layout_height="wrap_content"
    android:orientation="vertical" >

    <ProgressBar
        android:id="@+id/progressBar1"
        android:layout_width="wrap_content"
        android:layout_gravity="center"
        android:layout_height="wrap_content" />

</LinearLayout>

分离 BackGroundTask.java

public class BackGroundTask extends AsyncTask<Object, Void, String> {

    private ProgressDialog pDialog;
    public OnTaskCompleted listener = null;//Call back interface


    Context context;
    int pageNumber;

    public BackGroundTask(Context context1, OnTaskCompleted listener1, int pageNumber) {
        context = context1;
        listener = listener1;   //Assigning call back interface  through constructor
        this.pageNumber = pageNumber;
    }

    @Override
    protected void onPreExecute() {
        super.onPreExecute();

    }

    @Override
    protected String doInBackground(Object... params) {

        //My Background tasks are written here

        synchronized (this) {

            String url = Const.URL_WALLPAPERS_HD + pageNumber;
            String jsonStr = ServiceHandler.makeServiceCall(url, ServiceHandler.GET);
            Log.i("Url: ", "> " + url);

            Log.i("Response: ", "> " + jsonStr);
            return jsonStr;
        }

    }

    @Override
    protected void onPostExecute(String result) {
        super.onPostExecute(result);
        listener.onTaskCompleted(result);

    }

}

ServiceHanlder.java

public class ServiceHandler {

    static String response = null;
    public final static int GET = 1;
    public final static int POST = 2;


    public ServiceHandler() {

    }

    /**
     * Making service call
     *
     * @url - url to make request
     * @method - http request method
     */
    public static String makeServiceCall(String url, int method) {
        return makeServiceCall(url, method, null);
    }

    /**
     * Making service call
     *
     * @url - url to make request
     * @method - http request method
     * @params - http request params
     */
    public static String makeServiceCall(String url, int method,
                                  List<NameValuePair> params) {
        try {
            // http client
            DefaultHttpClient httpClient = new DefaultHttpClient();
            HttpEntity httpEntity = null;
            HttpResponse httpResponse = null;

            // Checking http request method type
            if (method == POST) {
                HttpPost httpPost = new HttpPost(url);
                // adding post params
                if (params != null) {
                    httpPost.setEntity(new UrlEncodedFormEntity(params));
                }
                Log.e("Selltis Request URL", url);
                httpResponse = httpClient.execute(httpPost);

            } else if (method == GET) {
                // appending params to url
                if (params != null) {
                    String paramString = URLEncodedUtils
                            .format(params, "utf-8");
                    url += paramString;

                    Log.i("Request URL", url);
                }
                HttpGet httpGet = new HttpGet(url);

                httpResponse = httpClient.execute(httpGet);

            }
            httpEntity = httpResponse.getEntity();
            response = EntityUtils.toString(httpEntity);

        } catch (UnsupportedEncodingException e) {
            e.printStackTrace();
            return "Fail";
        } catch (ClientProtocolException e) {
            e.printStackTrace();
            return "Fail";
        } catch (IOException e) {
            e.printStackTrace();
            return "Fail";
        }

        return response;

    }


}

加载更多界面

public interface OnLoadMoreListener {
     void onLoadMore();
}

了解从 asynctask 加载的 Web 服务数据的接口(interface)

public interface OnTaskCompleted{

    void onTaskCompleted(String response);
}

请让我知道这是否有效或对您有任何问题。最好使用 Volley 或 okHttp 库进行联网。

对于 ImageLoading，我使用了 Glide图书馆。