如何检查 RecyclerView 的第一项是否在屏幕上可见

Question

是否可以检查RecyclerView用户屏幕上的第一项或第二项是否可见？

例如当用户向下滚动时：

  if (first item not visible to user)  { 
      // do something
  }
  else if ( first item is visible){
      // do something
  }

我目前所做的是向我的回收器添加一个侦听器，以便当用户向下滚动时，它会执行某些操作并向上滚动。

recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        if (dy > 0) {
            mAccountLayout.setVisibility(View.GONE);
            mDateLayout.setVisibility(View.GONE);
            Log.d("SCROLLINGDOWN","SCROLL");
        } else {
            mAccountLayout.setVisibility(View.VISIBLE);
            mDateLayout.setVisibility(View.VISIBLE);
            Log.d("SCROLLINGUP","SCROLL");
        }
    }
});

但我需要的是检查第一项是否可见。

Answer 1

您可以在 中找到一些辅助方法RecyclerView.LayoutManager，例如，如果您使用 a LinearLayoutManager，请检查这些方法：

int findFirstCompletelyVisibleItemPosition() // Returns the adapter position of the first fully visible view.
int findFirstVisibleItemPosition() // Returns the adapter position of the first visible view.
int findLastCompletelyVisibleItemPosition() // Returns the adapter position of the last fully visible view.
int findLastVisibleItemPosition() // Returns the adapter position of the last visible view.

在此处查看完整文档。

在您的代码中：

recyclerView.setAdapter(adapter);
final LinearLayoutManager layoutManager = new LinearLayoutManager(context);
recyclerView.setLayoutManager(layoutManager);

recyclerView.addOnScrollListener(new RecyclerView.OnScrollListener() {

    @Override
    public void onScrolled(RecyclerView recyclerView, int dx, int dy) {
        if (layoutManager.findFirstVisibleItemPosition() > 0) {
            mAccountLayout.setVisibility(View.GONE);
            mDateLayout.setVisibility(View.GONE);
            Log.d("SCROLLINGDOWN","SCROLL");
        } else {
            mAccountLayout.setVisibility(View.VISIBLE);
            mDateLayout.setVisibility(View.VISIBLE);
            Log.d("SCROLLINGUP","SCROLL");
        }
    }
});

Answer 2

int firstVisiblePosition = layoutManager.findFirstVisibleItemPosition();
if (firstVisiblePosition  == 0) { do your thing )