我想把ListView改为RecyclerView。我想在RecyclerView中使用OnScrollListener的onScroll来确定用户是否滚动到列表的末尾。
我如何知道用户是否滚动到列表的末尾以便我可以从REST服务获取新数据?
我想把ListView改为RecyclerView。我想在RecyclerView中使用OnScrollListener的onScroll来确定用户是否滚动到列表的末尾。
我如何知道用户是否滚动到列表的末尾以便我可以从REST服务获取新数据?
当前回答
我使用了recyclerview。adapter的onBindViewHolder方法。
适配器:
public interface OnViewHolderListener {
void onRequestedLastItem();
}
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
...
if (position == getItemCount() - 1) onViewHolderListener.onRequestedLastItem();
}
片段(或活动):
@Override
public View onCreateView(LayoutInflater inflater, ViewGroup container, Bundle savedInstanceState) {
contentView = inflater.inflate(R.layout.comments_list, container, false);
recyclerView = (RecyclerView) mContentView.findViewById(R.id.my_recycler_view);
adapter = new Adapter();
recyclerView.setAdapter(adapter);
...
adapter.setOnViewHolderListener(new Adapter.OnViewHolderListener() {
@Override
public void onRequestedLastItem() {
//TODO fetch new data from webservice
}
});
return contentView;
}
其他回答
借助Kotlin扩展函数的强大功能,代码可以看起来更加优雅。把它放在你想要的任何地方(我把它放在一个ExtensionFunctions中。kt文件):
/**
* WARNING: This assumes the layout manager is a LinearLayoutManager
*/
fun RecyclerView.addOnScrolledToEnd(onScrolledToEnd: () -> Unit){
this.addOnScrollListener(object: RecyclerView.OnScrollListener(){
private val VISIBLE_THRESHOLD = 5
private var loading = true
private var previousTotal = 0
override fun onScrollStateChanged(recyclerView: RecyclerView,
newState: Int) {
with(layoutManager as LinearLayoutManager){
val visibleItemCount = childCount
val totalItemCount = itemCount
val firstVisibleItem = findFirstVisibleItemPosition()
if (loading && totalItemCount > previousTotal){
loading = false
previousTotal = totalItemCount
}
if(!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)){
onScrolledToEnd()
loading = true
}
}
}
})
}
然后像这样使用它:
youRecyclerView.addOnScrolledToEnd {
//What you want to do once the end is reached
}
这个解决方案基于Kushal Sharma的回答。然而,这是一个更好的,因为:
它使用onScrollStateChanged而不是onScroll。这样做比较好,因为每当RecyclerView中有任何类型的移动时,onScroll都会被调用,而onScrollStateChanged只在RecyclerView的状态改变时被调用。使用onScrollStateChanged将节省CPU时间,从而节省电池。 因为它使用扩展函数,所以可以在任何RecyclerView中使用。客户端代码只有一行。
@kushal @abdulaziz
为什么不使用这个逻辑呢?
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
int totalItemCount, lastVisibleItemPosition;
if (dy > 0) {
totalItemCount = _layoutManager.getItemCount();
lastVisibleItemPosition = _layoutManager.findLastVisibleItemPosition();
if (!_isLastItem) {
if ((totalItemCount - 1) == lastVisibleItemPosition) {
LogUtil.e("end_of_list");
_isLastItem = true;
}
}
}
}
这是另一种方法。它将与任何布局管理器工作。
使Adapter类抽象 然后在适配器类中创建一个抽象方法。load ()) 在onBindViewHolder中检查位置,如果最后调用load() 在活动或片段中创建适配器对象时重写load()函数。 在重载加载函数实现你的loadmore调用
为了详细了解,我写了一篇博客文章和示例项目 http://sab99r.com/blog/recyclerview-endless-load-more/
MyAdapter.java
public abstract class MyAdapter extends RecyclerView.Adapter<ViewHolder>{
@Override
public void onBindViewHolder(ViewHolder holder, int position) {
//check for last item
if ((position >= getItemCount() - 1))
load();
}
public abstract void load();
}
MyActivity.java
public class MainActivity extends AppCompatActivity {
List<Items> items;
MyAdapter adapter;
@Override
protected void onCreate(Bundle savedInstanceState) {
...
adapter=new MyAdapter(items){
@Override
public void load() {
//implement your load more here
Item lastItem=items.get(items.size()-1);
loadMore();
}
};
}
}
Create an abstract class and extends RecyclerView.OnScrollListener public abstract class EndlessRecyclerOnScrollListener extends RecyclerView.OnScrollListener { private int previousTotal = 0; private boolean loading = true; private int visibleThreshold; private int firstVisibleItem, visibleItemCount, totalItemCount; private RecyclerView.LayoutManager layoutManager; public EndlessRecyclerOnScrollListener(RecyclerView.LayoutManager layoutManager, int visibleThreshold) { this.layoutManager = layoutManager; this.visibleThreshold = visibleThreshold; } @Override public void onScrolled(RecyclerView recyclerView, int dx, int dy) { super.onScrolled(recyclerView, dx, dy); visibleItemCount = recyclerView.getChildCount(); totalItemCount = layoutManager.getItemCount(); firstVisibleItem = ((LinearLayoutManager)layoutManager).findFirstVisibleItemPosition(); if (loading) { if (totalItemCount > previousTotal) { loading = false; previousTotal = totalItemCount; } } if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) { onLoadMore(); loading = true; } } public abstract void onLoadMore();} in activity (or fragment) add addOnScrollListener to recyclerView LinearLayoutManager mLayoutManager = new LinearLayoutManager(this); recyclerView.setLayoutManager(mLayoutManager); recyclerView.addOnScrollListener(new EndlessRecyclerOnScrollListener(mLayoutManager, 3) { @Override public void onLoadMore() { //TODO ... } });
大多数答案是假设RecyclerView使用LinearLayoutManager,或GridLayoutManager,甚至StaggeredGridLayoutManager,或假设滚动是垂直或水平的,但没有人张贴一个完全通用的答案。
使用ViewHolder的适配器显然不是一个好的解决方案。一个适配器可能有超过1个RecyclerView在使用它。它“改编”了它们的内容。它应该是RecyclerView(它是一个负责当前显示给用户的类,而不是适配器,它只负责向RecyclerView提供内容),它必须通知您的系统需要更多的项(加载)。
下面是我的解决方案,只使用了RecyclerView (RecycerView. view)的抽象类。LayoutManager和RecycerView.Adapter):
/**
* Listener to callback when the last item of the adpater is visible to the user.
* It should then be the time to load more items.
**/
public abstract class LastItemListener extends RecyclerView.OnScrollListener {
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
// init
RecyclerView.LayoutManager layoutManager = recyclerView.getLayoutManager();
RecyclerView.Adapter adapter = recyclerView.getAdapter();
if (layoutManager.getChildCount() > 0) {
// Calculations..
int indexOfLastItemViewVisible = layoutManager.getChildCount() -1;
View lastItemViewVisible = layoutManager.getChildAt(indexOfLastItemViewVisible);
int adapterPosition = layoutManager.getPosition(lastItemViewVisible);
boolean isLastItemVisible = (adapterPosition == adapter.getItemCount() -1);
// check
if (isLastItemVisible)
onLastItemVisible(); // callback
}
}
/**
* Here you should load more items because user is seeing the last item of the list.
* Advice: you should add a bollean value to the class
* so that the method {@link #onLastItemVisible()} will be triggered only once
* and not every time the user touch the screen ;)
**/
public abstract void onLastItemVisible();
}
// --- Exemple of use ---
myRecyclerView.setOnScrollListener(new LastItemListener() {
public void onLastItemVisible() {
// start to load more items here.
}
}