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
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。
其他回答
我刚试了一下:
final LinearLayoutManager rvLayoutManager = new LinearLayoutManager(this);
rvMovieList = (RecyclerView) findViewById(R.id.rvMovieList);
rvMovieList.setLayoutManager(rvLayoutManager);
adapter = new MovieRecyclerAdapter(this, movies);
rvMovieList.setAdapter(adapter);
adapter.notifyDataSetChanged();
rvMovieList.addOnScrollListener(new OnScrollListener() {
boolean loading = true;
int pastVisiblesItems, visibleItemCount, totalItemCount;
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
visibleItemCount = rvLayoutManager.getChildCount();
totalItemCount = rvLayoutManager.getItemCount();
pastVisiblesItems = rvLayoutManager.findFirstVisibleItemPosition();
int lastitem = visibleItemCount + pastVisiblesItems;
if ( lastitem == totalItemCount
&& page < total_pages
&& !keyword.equals("") ) {
// hit bottom ..
String strnext;
if (page == total_pages - 1) {
int last = total_results - (page * 20);
strnext = String.format(getResources().getString(R.string.next), last);
} else {
strnext = String.format(getResources().getString(R.string.next), 20);
}
btNext.setText(strnext);
btNext.setVisibility(View.VISIBLE);
} else {
btNext.setVisibility(View.INVISIBLE);
}
if(pastVisiblesItems == 0 && page > 1){
// hit top
btPrev.setVisibility(View.VISIBLE);
} else {
btPrev.setVisibility(View.INVISIBLE);
}
}
});
我搞不清楚在哪里加载真或假,所以我试图删除它,这段代码工作如我所料。
@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;
}
}
}
}
做这些变量。
private int previousTotal = 0;
private boolean loading = true;
private int visibleThreshold = 5;
int firstVisibleItem, visibleItemCount, totalItemCount;
设置为滚动回收视图。
mRecyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
visibleItemCount = mRecyclerView.getChildCount();
totalItemCount = mLayoutManager.getItemCount();
firstVisibleItem = mLayoutManager.findFirstVisibleItemPosition();
if (loading) {
if (totalItemCount > previousTotal) {
loading = false;
previousTotal = totalItemCount;
}
}
if (!loading && (totalItemCount - visibleItemCount)
<= (firstVisibleItem + visibleThreshold)) {
// End has been reached
Log.i("Yaeye!", "end called");
// Do something
loading = true;
}
}
});
注意:确保你使用LinearLayoutManager作为RecyclerView的布局管理器。
LinearLayoutManager mLayoutManager;
mLayoutManager = new LinearLayoutManager(this);
mRecyclerView.setLayoutManager(mLayoutManager);
对于网格来说
GridLayoutManager mLayoutManager;
mLayoutManager = new GridLayoutManager(getActivity(), spanCount);
mRecyclerView.setLayoutManager(mLayoutManager);
有乐趣与你无尽的卷轴!!^ ^。
更新:mRecyclerView.setOnScrollListener()已弃用,只需替换为mRecyclerView.addOnScrollListener(),警告将消失!你可以从这个SO问题中读到更多。
由于Android现在正式支持Kotlin,这里是相同的更新-
使OnScrollListener
class OnScrollListener(val layoutManager: LinearLayoutManager, val adapter: RecyclerView.Adapter<RecyclerAdapter.ViewHolder>, val dataList: MutableList<Int>) : RecyclerView.OnScrollListener() {
var previousTotal = 0
var loading = true
val visibleThreshold = 10
var firstVisibleItem = 0
var visibleItemCount = 0
var totalItemCount = 0
override fun onScrolled(recyclerView: RecyclerView, dx: Int, dy: Int) {
super.onScrolled(recyclerView, dx, dy)
visibleItemCount = recyclerView.childCount
totalItemCount = layoutManager.itemCount
firstVisibleItem = layoutManager.findFirstVisibleItemPosition()
if (loading) {
if (totalItemCount > previousTotal) {
loading = false
previousTotal = totalItemCount
}
}
if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem + visibleThreshold)) {
val initialSize = dataList.size
updateDataList(dataList)
val updatedSize = dataList.size
recyclerView.post { adapter.notifyItemRangeInserted(initialSize, updatedSize) }
loading = true
}
}
}
然后像这样把它添加到你的RecyclerView中
recyclerView.addOnScrollListener(OnScrollListener(layoutManager, adapter, dataList))
要获得完整的代码示例,请参阅Github repo。
我的答案是一个改良版的努尔。我从一个ListView,在那里我有EndlessScrollListener(你可以很容易地在SO上找到许多答案)到一个RecyclerView,所以我想要一个endlessrecyscrolllistener轻松地更新我过去的监听器。
下面是代码,希望能有所帮助:
public abstract class EndlessScrollRecyclListener extends RecyclerView.OnScrollListener
{
// The total number of items in the dataset after the last load
private int previousTotalItemCount = 0;
private boolean loading = true;
private int visibleThreshold = 5;
int firstVisibleItem, visibleItemCount, totalItemCount;
private int startingPageIndex = 0;
private int currentPage = 0;
@Override
public void onScrolled(RecyclerView mRecyclerView, int dx, int dy)
{
super.onScrolled(mRecyclerView, dx, dy);
LinearLayoutManager mLayoutManager = (LinearLayoutManager) mRecyclerView
.getLayoutManager();
visibleItemCount = mRecyclerView.getChildCount();
totalItemCount = mLayoutManager.getItemCount();
firstVisibleItem = mLayoutManager.findFirstVisibleItemPosition();
onScroll(firstVisibleItem, visibleItemCount, totalItemCount);
}
public void onScroll(int firstVisibleItem, int visibleItemCount, int totalItemCount)
{
// If the total item count is zero and the previous isn't, assume the
// list is invalidated and should be reset back to initial state
if (totalItemCount < previousTotalItemCount)
{
this.currentPage = this.startingPageIndex;
this.previousTotalItemCount = totalItemCount;
if (totalItemCount == 0)
{
this.loading = true;
}
}
// If it’s still loading, we check to see if the dataset count has
// changed, if so we conclude it has finished loading and update the current page
// number and total item count.
if (loading && (totalItemCount > previousTotalItemCount))
{
loading = false;
previousTotalItemCount = totalItemCount;
currentPage++;
}
// If it isn’t currently loading, we check to see if we have breached
// the visibleThreshold and need to reload more data.
// If we do need to reload some more data, we execute onLoadMore to fetch the data.
if (!loading && (totalItemCount - visibleItemCount) <= (firstVisibleItem +
visibleThreshold))
{
onLoadMore(currentPage + 1, totalItemCount);
loading = true;
}
}
// Defines the process for actually loading more data based on page
public abstract void onLoadMore(int page, int totalItemsCount);
}
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 ... } });