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

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")

其他回答

对于那些在Kotlin中寻找答案的人:

fun getVisibleItem(recyclerView : RecyclerView) {
        recyclerView.addOnScrollListener(object: RecyclerView.OnScrollListener() {
            override fun onScrollStateChanged(recyclerView: RecyclerView, newState: Int) {
                 if(newState == RecyclerView.SCROLL_STATE_IDLE) {
                     val index = (recyclerView.layoutManager.findFirstVisibleItemPosition
                     //use this index for any operation you want to perform on the item visible on screen. eg. log(arrayList[index])
                 }
            }
        })
    }

您可以根据您的用例探索获取该职位的其他方法。

int findFirstCompletelyVisibleItemPosition()
int findLastVisibleItemPosition()
int findLastCompletelyVisibleItemPosition()

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。

最后,我找到了一个解决方案,从适配器中的onBindViewHolder事件了解当前项是否可见。

关键是来自LayoutManager的isViewPartiallyVisible方法。

在您的适配器中,您可以从RecyclerView中获得LayoutManager,它作为参数从onAttachedToRecyclerView事件中获得。

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).

以下线性/网格LayoutManager方法可用于检查哪些项是可见的。

int findFirstVisibleItemPosition();
int findLastVisibleItemPosition();
int findFirstCompletelyVisibleItemPosition();
int findLastCompletelyVisibleItemPosition();

如果你想跟踪屏幕上可见的项目,那么你可以参考下面的博客。

https://proandroiddev.com/detecting-list-items-perceived-by-user-8f164dfb1d05