RecyclerView ItemDecoration Spacing and Span

Question

I have a GridSpacingItemDecoration class that manages spacing and spans.
here is the code:

public class GridSpacingItemDecoration extends RecyclerView.ItemDecoration
{
    private int spanCount;
    private int spacing;
    private boolean includeEdge;
    private boolean rtl;

    public GridSpacingItemDecoration(boolean rtl, int spanCount, int spacing, boolean includeEdge)
    {
        this.rtl = rtl;
        this.spanCount = spanCount;
        this.spacing = spacing;
        this.includeEdge = includeEdge;
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state)
    {
        int position = parent.getChildAdapterPosition(view); // item position
        int column = position % spanCount; // item column

        if (includeEdge)
        {
            if (rtl)
            {
                outRect.right = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                outRect.left = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)
            }else {
                outRect.left = spacing - column * spacing / spanCount; // spacing - column * ((1f / spanCount) * spacing)
                outRect.right = (column + 1) * spacing / spanCount; // (column + 1) * ((1f / spanCount) * spacing)
            }

            if (position < spanCount)
            { // top edge
                outRect.top = spacing;
            }
            outRect.bottom = spacing; // item bottom
        } else
        {
            if (rtl){
                outRect.right = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                outRect.left = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
            }else {
                outRect.left = column * spacing / spanCount; // column * ((1f / spanCount) * spacing)
                outRect.right = spacing - (column + 1) * spacing / spanCount; // spacing - (column + 1) * ((1f /    spanCount) * spacing)
            }

            if (position >= spanCount)
            {
                outRect.top = spacing; // item top
            }
        }
    }
}

It works well when i want to have one or more columns. (shown in pictures below - all spacing and span works)

The problem is that i want to use a RecyclerView that has different ViewTypes with different spanCount. here is how i tried to do it:
defined in class:

public static ArrayList type = new ArrayList<>();

private int getTypeForPosition(int position)
{
    return type.get(position);
}

private final int HEADER = 0;
private final int CHILD = 1;
private int dpToPx(int dp)
{
    Resources r = getResources();
    return Math.round(TypedValue.applyDimension(TypedValue.COMPLEX_UNIT_DIP, dp, r.getDisplayMetrics()));
}

defined in method:

type.add(HEADER);
type.add(CHILD);
type.add(CHILD);
type.add(HEADER);
GridLayoutManager glm = new GridLayoutManager(getContext(), 2);
glm.setSpanSizeLookup(new GridLayoutManager.SpanSizeLookup() {
@Override
public int getSpanSize(int position) {
    switch(getTypeForPosition(position)) {
        case HEADER:
            return 2;
        default:
            return 1;
        }
    }
});
recyclerView.setLayoutManager(glm);
recyclerView.addItemDecoration(new GridSpacingItemDecoration(true, 1, dpToPx(8), true));
ClassAdapter classAdapter = new ClassAdapter(getContext(), classes);
recyclerView.setAdapter(classAdapter);

here is the result:

The problem is: the space between two columns in the same row (shown in picture). it seems to be 16, twice what i have choosed.
Question: How to customize GridSpacingItemDecoration class to have same space between all items?

RecyclerView ItemDecoration Spacing and Span

2 Answers