我需要知道哪些元素目前显示在我的RecyclerView。ListViews上没有与OnScrollListener.onScroll(…)方法等价的方法。我试图与view . getglobalvisibl勃起(…)工作,但黑客是太丑陋,并不总是工作太。
有人有什么想法吗?
我需要知道哪些元素目前显示在我的RecyclerView。ListViews上没有与OnScrollListener.onScroll(…)方法等价的方法。我试图与view . getglobalvisibl勃起(…)工作,但黑客是太丑陋,并不总是工作太。
有人有什么想法吗?
当前回答
Addendum: The proposed functions findLast...Position() do not work correctly in a scenario with a collapsing toolbar while the toolbar is expanded. It seems that the recycler view has a fixed height, and while the toolbar is expanded, the recycler is moved down, partially out of the screen. As a consequence the results of the proposed functions are too high. Example: The last visible item is told to be #9, but in fact item #7 is the last one that is on screen. This behaviour is also the reason why my view often failed to scroll to the correct position, i.e. scrollToPosition() did not work correctly (I finally collapsed the toolbar programmatically).
其他回答
您可以使用recyclerView.getChildAt()来获取每个可见的子视图,并在适配器代码中对这些视图设置一些convertview.setTag(index)标记将帮助您将其与适配器数据关联起来。
你可以找到recycle视图的第一个和最后一个可见的子视图,并检查你正在寻找的视图是否在范围内:
var visibleChild: View = rv.getChildAt(0)
val firstChild: Int = rv.getChildAdapterPosition(visibleChild)
visibleChild = rv.getChildAt(rv.childCount - 1)
val lastChild: Int = rv.getChildAdapterPosition(visibleChild)
println("first visible child is: $firstChild")
println("last visible child is: $lastChild")
第一个/最后一个可见子节点依赖于LayoutManager。 如果您正在使用LinearLayoutManager或GridLayoutManager,您可以使用
int findFirstVisibleItemPosition();
int findFirstCompletelyVisibleItemPosition();
int findLastVisibleItemPosition();
int findLastCompletelyVisibleItemPosition();
例如:
GridLayoutManager layoutManager = ((GridLayoutManager)mRecyclerView.getLayoutManager());
int firstVisiblePosition = layoutManager.findFirstVisibleItemPosition();
对于LinearLayoutManager,第一个/最后一个取决于适配器的顺序。不要从RecyclerView中查询子元素;LayoutManager可能更倾向于布局比缓存可见的更多的项。
上面的每个答案都是正确的,我也想添加一个快照从我的工作代码。
recycler.addOnScrollListener(new RecyclerView.OnScrollListener() {
@Override
public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
super.onScrollStateChanged(recyclerView, newState);
// Some code when initially scrollState changes
}
@Override
public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
super.onScrolled(recyclerView, dx, dy);
// Some code while the list is scrolling
LinearLayoutManager lManager = (LinearLayoutManager) recyclerView.getLayoutManager();
int firstElementPosition = lManager.findFirstVisibleItemPosition();
}
});
对于StaggeredGridLayoutManager执行以下操作:
RecyclerView rv = findViewById(...);
StaggeredGridLayoutManager lm = new StaggeredGridLayoutManager(...);
rv.setLayoutManager(lm);
要获得可见的项目视图:
int[] viewsIds = lm.findFirstCompletelyVisibleItemPositions(null);
ViewHolder firstViewHolder = rvPlantios.findViewHolderForLayoutPosition(viewsIds[0]);
View itemView = viewHolder.itemView;
记得检查它是否为空。