RecyclerView 获取第一个可见项的高度

Question

How can i calculate the height of the first visible item in my recyclerview ?

  public void onScrollStateChanged(RecyclerView recyclerView, int newState) {
        switch (newState) {
            case RecyclerView.SCROLL_STATE_IDLE:
                Log.d("scroll_stop","The RecyclerView is not scrolling : ");
                View firstItemView = mGLM.findViewByPosition(mGLM.findFirstVisibleItemPosition());

                View mVizibleView= mPlm.findViewByPosition(mGLM.findFirstVisibleItemPosition());
}
  });

But this give me the full height of the view

Answer 1

Taking the Size of any RecyclerView Item is pointless, If you getHeight() or getWidth() of any item it's just gonna give a Null Error and your app is gonna crash.

What you can do, Is to Use your ViewHolder from recyclerView Adapter and First set a Specific Height to any Item you want and Then use that Height somewhere Else.

Look at the Code Below, Maybe helps:

 class myViewHolder extends RecyclerView.ViewHolder { RemaltiveLayout itemLayout; public myViewHolder(View itemView) { super(itemView); itemLayout = (RemaltiveLayout) itemView.findViewById(R.id.myItemLayout); itemLayout.getLayoutParams().height = res.getDimensionPixelSize(R.dimen.height_value); }

You should be able to use item at a specific location position as well

This is not gonna work with Width though, cause items are always being stretched to fill columns of layoutManager

Answer 2

Steps to get first item height:

1. Get the layout manager from the recyclerview reference in onScrolled()
2. Get the first the visible item position using layoutManager.findFirstVisibleItemPosition()
3. If fist visible item position is 0 then get the 0th child height layoutManager.getChildAt(0)

Sample code:

RecyclerView.OnScrollListener scrollListener = new RecyclerView.OnScrollListener() {
    @Override
    public void onScrolled(@NonNull RecyclerView recyclerView, int dx, int dy) {
        super.onScrolled(recyclerView, dx, dy);
        LinearLayoutManager layoutManager = (LinearLayoutManager) recyclerView.getLayoutManager();

        if (layoutManager != null) {
            int child0Height = 0;
            int currentFirstVisibleItem = layoutManager.findFirstVisibleItemPosition();
            if (currentFirstVisibleItem == 0) {
                final View childAt0 = layoutManager.getChildAt(0);
                if (childAt0 != null) {
                    child0Height = childAt0.getHeight();
                }
            }
        }
    }
};