删除RecyclerView页脚视图

Question

我正在从外部数据库下载数据，并在用户向下滚动时填充数组。下载数据时，我显示了一个页脚视图（loadmoreview）。我目前的困境是，当用户到达列表末尾时，即没有更多数据可下载时，删除此页脚视图。

下载：

private void DownloadUsersClassic(final String start, final String finish) {
   loadingMore = true;
   Log.i("DownloadUsersClassic", "started");
   StringRequest postReq = new StringRequest(Request.Method.POST, download_leaderboard_classic, new Response.Listener<String>() {
       @Override
       public void onResponse(String response) {
          if (response.length() > 10) {
              //populate arrays from json
              if (arr_userid.size() < 14) {
                  //set adapter the first time the user scrolls
                  mAdapter = new CustomAdapter(getActivity(), arr_userid, arr_username, arr_photo, arr_level, arr_date, true);
                  rv.setAdapter(mAdapter);
              } else {
                  //call notifyDataSetChanged() at the other scrolls
                  mAdapter.notifyDataSetChanged();
              }
          else {
               //there is no more data to download
               mAdapter = new CustomAdapter(getActivity(), arr_userid, arr_username, arr_photo, arr_level, arr_date, false);
               mAdapter.notifyDataSetChanged();
          }
      }
}, new Response.ErrorListener() {
    @Override
    public void onErrorResponse(VolleyError error) {
        Log.i("VOLLEY_ERROR", error.toString());
    }
}) {
    @Override
    protected Map<String, String> getParams() {
        Map<String, String> params = new HashMap<String, String>();
        params.put("start", start);
        params.put("finish", finish);
        return params;
    }
};

适配器：

public class CustomAdapter extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
        ArrayList<String> arr_userid = new ArrayList<String>();
        ArrayList<String> arr_username = new ArrayList<String>();
        ArrayList<String> arr_photo = new ArrayList<String>();
        ArrayList<String> arr_level = new ArrayList<String>();
        ArrayList<String> arr_date = new ArrayList<String>();
        boolean show_footer;
        public LayoutInflater inflater;
        public static final int TYPE_ITEM = 1;
        public static final int TYPE_FOOTER = 2;
        Context context;
        public CustomAdapter(Context context, ArrayList<String> arr_userid, ArrayList<String> arr_username, ArrayList<String> arr_photo, ArrayList<String> arr_level, ArrayList<String> arr_date, boolean show_footer) {
            super();
            this.arr_userid = arr_userid;
            this.arr_username = arr_username;
            this.arr_photo = arr_photo;
            this.arr_level = arr_level;
            this.arr_date = arr_date;
            this.show_footer = show_footer;
            this.inflater = (LayoutInflater)context.getSystemService(Context.LAYOUT_INFLATER_SERVICE);
        }
        public class GenericViewHolder extends RecyclerView.ViewHolder {
            public TextView txtName, txtPoints, txtDate;
            public ImageView ivUser;
            public LinearLayout llLoadmore;
            public GenericViewHolder(View v) {
                super(v);
                txtName = (TextView) v.findViewById(R.id.txtName);
                txtPoints = (TextView) v.findViewById(R.id.txtPoints);
                txtDate = (TextView) v.findViewById(R.id.txtDate);
                ivUser = (ImageView) v.findViewById(R.id.ivUser);
                llLoadmore = (LinearLayout) v.findViewById(R.id.loadmore);
            }
        }
        class FooterViewHolder extends RecyclerView.ViewHolder {
            TextView tvloadmore;
            public FooterViewHolder (View itemView) {
                super (itemView);
                this.tvloadmore = (TextView) itemView.findViewById (R.id.tvloadmore);
            }
        }

        public void add(int position, String item) {
            arr_userid.add(position, item);
            notifyItemInserted(position);
        }
        public void remove(String item) {
            int position = arr_userid.indexOf(item);
            arr_userid.remove(position);
            notifyItemRemoved(position);
        }
        public CustomAdapter(ArrayList<String> myDataset) {
            arr_userid = myDataset;
        }
        @Override
        public RecyclerView.ViewHolder onCreateViewHolder (ViewGroup parent, int viewType) {
            if(viewType == TYPE_FOOTER) {
                View v = LayoutInflater.from (parent.getContext ()).inflate (R.layout.loadmore, parent, false);
                return new FooterViewHolder (v);
            } else if(viewType == TYPE_ITEM) {
                View v = LayoutInflater.from (parent.getContext ()).inflate (R.layout.leaderboard_row, parent, false);
                return new GenericViewHolder (v);
            }
            return null;
        }

        @Override
        public void onBindViewHolder(RecyclerView.ViewHolder holder, int position) {
            if(holder instanceof FooterViewHolder) {
                FooterViewHolder footerHolder = (FooterViewHolder) holder;
                footerHolder.tvloadmore.setText("Footer");
                footerHolder.tvloadmore.setOnClickListener (new View.OnClickListener () {
                    @Override
                    public void onClick (View view) {
                        Toast.makeText (getActivity(), "Clicked Footer", Toast.LENGTH_SHORT).show ();
                    }
                });
            } else if(holder instanceof GenericViewHolder) {
                GenericViewHolder genericViewHolder = (GenericViewHolder) holder;
                final String name = arr_username.get(position);
                genericViewHolder.txtName.setText(arr_username.get(position));
                genericViewHolder.txtPoints.setText(arr_level.get(position) + " Levels");
                String year = arr_date.get(position).substring(0, 4);
                String month = arr_date.get(position).substring(5, 7);
                String day = arr_date.get(position).substring(8, 10);
                genericViewHolder.txtDate.setText(month + "." + day + "." + year);
                if (!arr_photo.get(position).equals("")) {
                    Picasso.with(getActivity())
                            .load(arr_photo.get(position))
                            .into(genericViewHolder.ivUser);
                } else {
                    genericViewHolder.ivUser.setImageDrawable(null);
                }
            }
        }
        @Override
        public int getItemCount() {
            if (show_footer) {
                return arr_userid.size() + 1; //+1 is for the footer as it's an extra item
            } else {
                return arr_userid.size();
            }
        }
        @Override
        public int getItemViewType (int position) {
            if (show_footer) {
                if (isPositionFooter(position)) {
                    return TYPE_FOOTER;
                }
                return TYPE_ITEM;
            } else {
                return TYPE_ITEM;
            }
        }
        private boolean isPositionFooter (int position) {
            return position == arr_userid.size ();
        }
    }

onScrollListener:

rv.addOnScrollListener(new RecyclerView.OnScrollListener() {
            @Override
            public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
                super.onScrolled(recyclerView, dx, dy);
                visibleItemCount = rv.getChildCount();
                totalItemCount = llm.getItemCount();
                firstVisibleItem = llm.findFirstVisibleItemPosition();
                if (loading) {
                    if (totalItemCount > previousTotal) {
                        loading = false;
                        previousTotal = totalItemCount;
                    }
                }
                if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) {
                    // End has been reached
                    //we need the -1 otherwise 1 item will be missed the first time we scroll. I don't know why only the first
                    //time but the point it's working this way
                    DownloadUsersClassic(String.valueOf(totalItemCount-1), String.valueOf(num_loadfinish));
                    loading = true;
                }
            }
        });

看到适配器末尾的布尔变量了吗？我正试图用它来告诉适配器我是否需要页脚。当我下载数据时是真的：

mAdapter = new CustomAdapter(getActivity(), arr_userid, arr_username, arr_photo, arr_level, arr_date, true);

当到达终点时，这是错误的：

mAdapter = new CustomAdapter(getActivity(), arr_userid, arr_username, arr_photo, arr_level, arr_date, false);

问题是，什么都没发生。页脚保持不变。我打不到

mAdapter = new CustomAdapter(getActivity(), arr_userid, arr_username, arr_photo, arr_level, arr_date, false);
rv.setAdapter(mAdapter);

因为它重新初始化适配器并跳到顶部。

Answer 1

适配器类中的小修改：-

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

在调用loadMore时插入null作为项目，如下所示：-

 dataSet.add(null);
 mAdapter.notifyItemInserted(dataSet.size() - 1);

从回收器中移除物品装载完成后查看更多：-

dataset.remove(dataSet.size() - 1);
mAdapter.notifyItemRemoved(dataSet.size());

仅此而已。希望这能帮助

Answer 2

几个小时后我发现了。如果您确定没有更多数据可下载，请添加：

mAdapter.hideFooter();
mAdapter.notifyDataSetChanged();

将此添加到适配器：

public void hideFooter() {
     show_footer = false;
}

这告诉适配器隐藏末尾的页脚。

查看本教程了解完整的代码。