Question

我遵循Vilen关于SO Put an indeterminate progressbar as footer in a RecyclerView grid的优秀答案，了解如何使用ProgressBar实现无限滚动回收视图。

我自己实现了它并且它有效，但我想扩展这个例子。我想在recyclerview的顶部添加额外的项目，类似于Facebook在添加新状态更新时的操作方式。

我无法在列表中成功添加额外的项目 - 这是我在其MainActivity中添加到Vilen代码中的代码：

@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＆＃34;添加＆＃34;按钮：

Adding a new item

当我向下滚动时，我得到两个旋转器而不是一个：

Scroll down

当旋转器完成并且下一个5个物品被加载时，旋转器仍在那里：

after spinner

我做错了什么？

Answer 1

问题在于，当您添加新项目时，内部EndlessRecyclerOnScrollListener不了解它并反击破坏。事实上，EndlessRecyclerOnScrollListener的回答有一些限制和可能的问题，例如如果你一次加载1项，它将无法正常工作。所以这是一个增强版本。

摆脱EndlessRecyclerOnScrollListener我们不再需要它了

将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);
        }
    }
}

更改活动类

中的代码

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，请告诉我这是否适合您。

Answer 2

我想我已经明白了。

我忘了打电话给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，代码就会生效，但是，您会看到在微调器完成旋转后，项目编号将无法正常增加。

increment

这是因为＆＃34;新增＆＃34;最重要的项目计为实际项目（我们可以称之为＆＃34;项目0和＃34;），这导致增量按21跳过，但是实际上数字21已成为项目0。在第22项之前，有21个实际项目。

使用ProgressBar在底部向Endless Scroll RecyclerView添加项目

2 个答案: