如何检查RecyclerView的第一项在屏幕上是否可见 [英] How to check if first item of RecyclerView is visible on the screen

问题描述

是否可以检查RecyclerView的第一项或第二项在用户的屏幕上是否可见?

Is it possible to check if the first or second item of the RecyclerView is visible on the screen of the user?

例如，当用户向下滚动时:

For example when the user scrolls down:

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

我目前要做的是在回收站中添加一个侦听器，以便当用户向下滚动时，它可以执行某些操作并向上滚动.

What I currently do is I add a listener to my recycler so that when the user scrolls down, it will do something and scroll up.

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");
        }
    }
});

但是我需要检查第一项是否可见.

But what I need is to check if the first item is visible or not.

推荐答案

您可以在RecyclerView.LayoutManager中找到一些帮助方法，例如，如果使用LinearLayoutManager，请检查以下方法:

You can find some helper methods in RecyclerView.LayoutManager, for example, if you use a LinearLayoutManager, check these methods:

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.

在此处中查看完整文档>.

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");
        }
    }
});

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