java - ScrollToPosition doesnt work with recyclerview in a horizontal linearlayoutmanager and spacings

Question

I tried to implement a carousel view with snapping. I add spacing to the cards in the recyclerview with itemdecorations, that add spacing between the cards and enough spacing to center the first and last item. When I now load the recyclerview, the recyclerview doesnt start with the first card centered. I tried to fix it with layoutmanager.scrollToPositionWithOffset, and it starts slightly less offset, but I can't get it to start at the beginning. This is my onCreate where I load the recyclerview:

@Override
    protected void onCreate(Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setContentView(R.layout.activity_player);

        layoutManager = new LinearLayoutManager(this, RecyclerView.HORIZONTAL, false);

        RecyclerView recyclerView = findViewById(R.id.coverList);
        recyclerView.setHasFixedSize(false);
        recyclerView.setLayoutManager(layoutManager);

        Song song = new Song(null, "Test", "Test", 0, 0);
        List<Song> songs = new ArrayList<>();
        songs.add(song);
        songs.add(song);
        songs.add(song);
        songs.add(song);
        songs.add(song);
        songs.add(song);

        CoverRecyclerViewAdapter adapter = new CoverRecyclerViewAdapter(songs);
        recyclerView.setAdapter(adapter);

        int spacing = getResources().getDimensionPixelSize(R.dimen.carousel_spacing);
        recyclerView.addItemDecoration(new CarouselItemDecoration(spacing));

        new PagerSnapHelper().attachToRecyclerView(recyclerView);
    }

This is my itemdecoration class:

public class CarouselItemDecoration extends RecyclerView.ItemDecoration {
    private int innerSpacing;

    public CarouselItemDecoration(@Px int innerSpacing) {
        this.innerSpacing = innerSpacing;
    }

    @Override
    public void getItemOffsets(@NonNull Rect outRect, @NonNull View view, @NonNull RecyclerView parent, @NonNull RecyclerView.State state) {
        super.getItemOffsets(outRect, view, parent, state);

        int itemPosition = parent.getChildAdapterPosition(view);

        int itemWidth = view.getLayoutParams().width;
        int offset = (parent.getWidth() - itemWidth) / 2;

        if(itemPosition == 0) {
            outRect.left = offset;
        } else {
            outRect.left = innerSpacing / 2;
        }
        if(itemPosition == state.getItemCount() - 1) {
            outRect.right = offset;
        } else {
            outRect.right = innerSpacing / 2;
        }
    }
}

How can I load my recyclerview centered on the first card?

question from:https://stackoverflow.com/questions/65926923/scrolltoposition-doesnt-work-with-recyclerview-in-a-horizontal-linearlayoutmanag

Answer 1

Waitting for answers