RecyclerView's ItemDecorator to achieve equal spacing around the items when using a GridLayoutManager

EqualSpacingGridItemDecorator.java

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

public class EqualSpacingGridItemDecorator extends RecyclerView.ItemDecoration {

    private final int padding;

    public EqualSpacingGridItemDecorator(int padding) {
        this.padding = padding;
    }

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

        GridLayoutManager.LayoutParams layoutParams = (GridLayoutManager.LayoutParams) view.getLayoutParams();
        GridLayoutManager gridLayoutManager = (GridLayoutManager) parent.getLayoutManager();
        float spanSize = layoutParams.getSpanSize();
        float totalSpanSize = gridLayoutManager.getSpanCount();

        float n = totalSpanSize / spanSize; // num columns
        float c = layoutParams.getSpanIndex() / spanSize; // column index

        float leftPadding = padding * ((n - c) / n);
        float rightPadding = padding * ((c + 1) / n);

        int position = parent.getChildAdapterPosition(view);

        //Add top padding only to first row
        if (position == 0 || position == 1) outRect.top = padding;

        outRect.left = (int) leftPadding;
        outRect.right = (int) rightPadding;
        outRect.bottom = padding;
    }
}