Decorating RecyclerView (with GridLayoutManager) to display divider between items

Question

What\'s the best and easiest way to decorate RecyclerView to have such look & feel?

Answer 1

Here's a simpler and more user-friendly implementation:

public class MediaSpaceDecoration extends RecyclerView.ItemDecoration {
    private final int spacing;
    private final List allowedViewTypes = Arrays.asList(
            R.layout.item_image,
            R.layout.item_blur);

    public MediaSpaceDecoration(int spacing) {
        this.spacing = spacing;
    }

    @Override
    public void getItemOffsets(Rect outRect,
                               View view,
                               RecyclerView parent,
                               RecyclerView.State state) {
        final int position = parent.getChildAdapterPosition(view);
        if (!isMedia(parent, position)) {
            return;
        }

        final int totalSpanCount = getTotalSpanCount(parent);
        int spanSize = getItemSpanSize(parent, position);
        if (totalSpanCount == spanSize) {
            return;
        }

        outRect.top = isInTheFirstRow(position, totalSpanCount) ? 0 : spacing;
        outRect.left = isFirstInRow(position, totalSpanCount) ? 0 : spacing / 2;
        outRect.right = isLastInRow(position, totalSpanCount) ? 0 : spacing / 2;
        outRect.bottom = 0; // don't need
    }

    private boolean isInTheFirstRow(int position, int spanCount) {
        return position < spanCount;
    }

    private boolean isFirstInRow(int position, int spanCount) {
        return position % spanCount == 0;
    }

    private boolean isLastInRow(int position, int spanCount) {
        return isFirstInRow(position + 1, spanCount);
    }

    private int getTotalSpanCount(RecyclerView parent) {
        final RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        return layoutManager instanceof GridLayoutManager
            ? ((GridLayoutManager) layoutManager).getSpanCount()
            : 1;
    }

    private int getItemSpanSize(RecyclerView parent, int position) {
        final RecyclerView.LayoutManager layoutManager = parent.getLayoutManager();
        return layoutManager instanceof GridLayoutManager
            ? ((GridLayoutManager) layoutManager).getSpanSizeLookup().getSpanSize(position)
            : 1;
    }

    private boolean isMedia(RecyclerView parent, int viewPosition) {
        final RecyclerView.Adapter adapter = parent.getAdapter();
        final int viewType = adapter.getItemViewType(viewPosition);
        return allowedViewTypes.contains(viewType);
    }
}

I also check before setting the outRect because I have various spanSizes for each viewType and I need to add an extra middle-space only for allowedViewTypes. You can easily remove that verification and the code would be even simpler. It looks like this for me: