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
有一个易于使用的名为paginate的库。支持ListView和RecyclerView(线性布局,GridLayout和StaggeredGridLayout)。
这是该项目在Github上的链接
其他回答
我会尝试扩展使用的LayoutManager(例如LinearLayoutManager)和覆盖scrollVerticallyBy()方法。首先,我会先调用super,然后检查返回的整数值。如果值等于0,则到达底部或顶部边界。然后我将使用findLastVisibleItemPosition()方法来找出到达哪个边界,并在需要时加载更多数据。只是一个想法。
此外,您甚至可以从该方法中返回您的值,允许滚动并显示“loading”指示器。
我有一个关于如何使用RecyclerView进行分页的非常详细的示例。在高层次,我有一个设置PAGE_SIZE,让我们说30。所以我请求30个项目,如果我得到30个,我就请求下一页。如果我得到的条目少于30个,我就标记一个变量来指示已经到达最后一页,然后停止请求更多的页面。看看吧,告诉我你的想法。
https://medium.com/@etiennelawlor/pagination-with-recyclerview-1cb7e66a502b
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.
}
}
我检测加载事件的方法不是检测滚动,而是监听最后一个视图是否附加。如果附加了最后一个视图,我认为这是加载更多内容的时机。
class MyListener implements RecyclerView.OnChildAttachStateChangeListener {
RecyclerView mRecyclerView;
MyListener(RecyclerView view) {
mRecyclerView = view;
}
@Override
public void onChildViewAttachedToWindow(View view) {
RecyclerView.Adapter adapter = mRecyclerView.getAdapter();
RecyclerView.LayoutManager mgr = mRecyclerView.getLayoutManager();
int adapterPosition = mgr.getPosition(view);
if (adapterPosition == adapter.getItemCount() - 1) {
// last view was attached
loadMoreContent();
}
@Override
public void onChildViewDetachedFromWindow(View view) {}
}
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);
}