将项目添加到 Endless Scroll RecyclerView，底部有 ProgressBar

Question

我关注了 Vilen 在 SO:Put an indeterminate progressbar as footer in a RecyclerView grid 上的出色回答，了解如何使用 ProgressBar 实现无限滚动回收视图。

我自己实现了它，它可以工作，但我想扩展这个例子。我想在 recyclerview 顶部添加额外的项目，类似于 Facebook 在添加新状态更新时的做法。

我无法成功地将额外的项目添加到列表中 - 这是我在 Vilen 的 MainActivity 代码中添加的代码：

@Override
public boolean onCreateOptionsMenu(Menu menu) {
    // Inflate the menu; this adds items to the action bar if it is present.
    getMenuInflater().inflate(R.menu.menu_main, menu);
    return true;
}

@Override
public boolean onOptionsItemSelected(MenuItem item) {

    int id = item.getItemId();

    if (id == R.id.add) {
        myDataset.add(0, "Newly added");
        mRecyclerView.smoothScrollToPosition(0);
        mAdapter.notifyItemInserted(0);
}
return super.onOptionsItemSelected(item);
}

当我点击“添加”按钮时：

当我向下滚动时，我得到两个微调器而不是一个：

当微调器完成并加载接下来的 5 个项目时，微调器仍然存在：

我做错了什么？

Answer 1

我想我明白了。

我忘记调用 notifyItemRangeChanged。

@Override
public boolean onOptionsItemSelected(MenuItem item) {
    // Handle action bar item clicks here. The action bar will
    // automatically handle clicks on the Home/Up button, so long
    // as you specify a parent activity in AndroidManifest.xml.
    int id = item.getItemId();

    //noinspection SimplifiableIfStatement
    if (id == R.id.add) {
        myDataset.add(0, "Newly added");
        mAdapter.notifyItemInserted(0);
        mAdapter.notifyItemRangeChanged(1, myDataset.size());
        mRecyclerView.smoothScrollToPosition(0);
}
return super.onOptionsItemSelected(item);
}

添加后，代码将起作用，但是，您会看到微调器完成旋转后，项目编号不会正确增加。

这是因为顶部的“新添加”项算作实际项（我们可以称其为“项 0”），这会导致增量移位 1 就像 21 已被跳过，但实际上数字 21 已变为第 0 项。也就是说，第 22 项之前有 21 个实际项。

Answer 2

问题是当您添加新项目时，内部EndlessRecyclerOnScrollListener 不知道它并且计数器会损坏。 事实上，EndlessRecyclerOnScrollListener 的回答有一些限制和可能的问题，例如如果您一次加载 1 个项目，它将不起作用。所以这里是一个增强版。

1. 摆脱EndlessRecyclerOnScrollListener，我们不再需要它了

2. 将您的适配器更改为包含滚动侦听器的适配器

   public class MyAdapter<T> extends RecyclerView.Adapter<RecyclerView.ViewHolder> {
   
       private final int VIEW_ITEM = 1;
       private final int VIEW_PROG = 0;
   
       private List<T> mDataset;
   
       // The minimum amount of items to have below your current scroll position before loading more.
       private int visibleThreshold = 2;
       private int lastVisibleItem, totalItemCount;
       private boolean loading;
       private OnLoadMoreListener onLoadMoreListener;
   
       public MyAdapter(List<T> myDataSet, RecyclerView recyclerView) {
           mDataset = myDataSet;
   
           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 mDataset.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(android.R.layout.simple_list_item_1, parent, false);
   
               vh = new TextViewHolder(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 TextViewHolder) {
               ((TextViewHolder) holder).mTextView.setText(mDataset.get(position).toString());
           } else {
               ((ProgressViewHolder) holder).progressBar.setIndeterminate(true);
           }
       }
   
       public void setLoaded() {
           loading = false;
       }
   
       @Override
       public int getItemCount() {
           return mDataset.size();
       }
   
       public void setOnLoadMoreListener(OnLoadMoreListener onLoadMoreListener) {
           this.onLoadMoreListener = onLoadMoreListener;
       }
   
       public interface OnLoadMoreListener {
           void onLoadMore();
       }
   
       public static class TextViewHolder extends RecyclerView.ViewHolder {
           public TextView mTextView;
   
           public TextViewHolder(View v) {
               super(v);
               mTextView = (TextView) v.findViewById(android.R.id.text1);
           }
       }
   
       public static class ProgressViewHolder extends RecyclerView.ViewHolder {
           public ProgressBar progressBar;
   
           public ProgressViewHolder(View v) {
               super(v);
               progressBar = (ProgressBar) v.findViewById(R.id.progressBar);
           }
       }
   }
   

3. 在 Activity 类中更改代码

   mAdapter = new MyAdapter<String>(myDataset, mRecyclerView);
   mRecyclerView.setAdapter(mAdapter);
   
   mAdapter.setOnLoadMoreListener(new MyAdapter.OnLoadMoreListener() {
       @Override
       public void onLoadMore() {
           //add progress item
           myDataset.add(null);
           mAdapter.notifyItemInserted(myDataset.size() - 1);
   
           handler.postDelayed(new Runnable() {
               @Override
               public void run() {
                   //remove progress item
                   myDataset.remove(myDataset.size() - 1);
                   mAdapter.notifyItemRemoved(myDataset.size());
                   //add items one by one
                   for (int i = 0; i < 15; i++) {
                       myDataset.add("Item" + (myDataset.size() + 1));
                       mAdapter.notifyItemInserted(myDataset.size());
                   }
                   mAdapter.setLoaded();
                   //or you can add all at once but do not forget to call mAdapter.notifyDataSetChanged();
               }
           }, 2000);
           System.out.println("load");
       }
   });
   

其余部分保持不变，让我知道这是否适合您。