问题描述
我遵循了 Vilen 对 SO 的出色回答:在 RecyclerView 网格中放置一个不确定的进度条作为页脚，了解如何使用 ProgressBar 实现无限滚动的 RecyclerView.
I followed Vilen's excellent answer on SO: Put an indeterminate progressbar as footer in a RecyclerView grid on how to implement an endless scroll recyclerview with ProgressBar.
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做法.
I implemented it myself and it works but I would like to extend the example. I want to add extra items at the top of the recyclerview, similar to how Facebook does it when you add a new status update.
我无法成功地将额外的项目添加到列表中 - 这是我在他的 MainActivity 中添加到 Vilen 代码中的代码:
I was not able to add extra items onto the list successfully - here is my code that I added onto Vilen's code in his MainActivity:
@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:
When I clicked the "Add" button:
当我向下滚动时，我得到两个微调器而不是一个:
When I scroll down, I get two spinners instead of one:
当微调器完成并加载了接下来的 5 个项目时，微调器仍在那里:
When the spinners finish and the next 5 items are loaded, the spinner is still there:
我做错了什么?
推荐答案
问题是当您添加新项目时，内部 EndlessRecyclerOnScrollListener 不知道它并且计数器中断.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，它将无法正常工作.所以这是一个增强版.
The problem is that when you add new item internal EndlessRecyclerOnScrollListener doesn't know about it and counters breaking.As a matter of fact answer with EndlessRecyclerOnScrollListener has some limitations and possible problems, e.g. if you load 1 item at a time it will not work. So here is an enhanced version.
- 去掉
EndlessRecyclerOnScrollListener我们不再需要它了 将您的适配器更改为包含滚动侦听器的适配器
- Get rid of
EndlessRecyclerOnScrollListenerwe don't need it anymore Change your adapter to this which contains scroll listener
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);
}
}
}
在 Activity 类中更改代码
Change code in Activity class
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");
}
});
其余保持不变，如果这对您有用，请告诉我.
The rest remains unchanged, let me know if this works for you.
这篇关于使用底部的 ProgressBar 将项目添加到 Endless Scroll RecyclerView的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持！