GridSpaceItemDecoration.java

import android.graphics.Rect;
import android.support.v7.widget.RecyclerView;
import android.view.View;

public class GridSpaceItemDecoration extends RecyclerView.ItemDecoration {

    private final int mSpanCount;
    private final int mSpace;
    private final int[] mHorizontalSpaces;

    public GridSpaceItemDecoration(int spanCount, int space) {
        mSpanCount = spanCount;
        mSpace = space;
        mHorizontalSpaces = new int[mSpanCount];
        for (int i = 0; i < mSpanCount; i++) {
            mHorizontalSpaces[i] = space * (i + 1) / mSpanCount;
        }
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        final int position = parent.getChildPosition(view);
        final int spanIndex = position % mSpanCount;
        outRect.left = mHorizontalSpaces[mSpanCount - spanIndex - 1];
        outRect.right = mHorizontalSpaces[spanIndex];
        outRect.bottom = mSpace;
    }
}