A kind of ItemDecoration to draw gridlines with specific color and size.

GridlinesItemDecoration.java

/**
 * A kind of {@link android.support.v7.widget.RecyclerView.ItemDecoration} to draw gridlines with
 * specific color and size. It assumes every item at same column has the same width and don't draw border.
 */
public class GridlinesItemDecoration extends RecyclerView.ItemDecoration {
    private static final String TAG = GridlinesItemDecoration.class.getSimpleName();

    private int mDividerSize;
    private Paint mPaint;

    private final Rect mBounds = new Rect();

    public GridlinesItemDecoration(@ColorInt int color, @IntRange(from = 0) int size) {
        mDividerSize = size;

        mPaint = new Paint();
        mPaint.setColor(color);
        mPaint.setStrokeWidth(mDividerSize);
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView recyclerView, RecyclerView.State state) {
        final int padding = mDividerSize / 2;
        outRect.set(padding, padding, padding, padding);
    }

    @Override
    public void onDraw(Canvas canvas, RecyclerView parent, RecyclerView.State state) {
        canvas.save();

        // Get boundary of parent.
        final int top = 0;
        final int bottom = parent.getHeight();
        final int left = 0;
        final int right = parent.getWidth();

        int columnCount = 0;
        final int childCount = parent.getChildCount();

        // Loop first column to draw vertical divider.
        int x = 0;
        for (int i = 0; i < childCount; i++) {
            columnCount++;

            // Get width of child view.
            final View child = parent.getChildAt(i);
            parent.getLayoutManager().getDecoratedBoundsWithMargins(child, mBounds);
            final int width = mBounds.right - mBounds.left;

            // Draw vertical divider if space enough.
            x += width + mDividerSize;
            if (x < right) {
                canvas.drawLine(x, top, x, bottom, mPaint);
            } else {
                break;
            }
        }

        // Loop every row to draw horizontal divider.
        int y = 0;
        for (int i = 0; i < childCount; i += columnCount) {
            // Get height of child view.
            final View child = parent.getChildAt(i);
            parent.getLayoutManager().getDecoratedBoundsWithMargins(child, mBounds);
            final int height = mBounds.bottom - mBounds.top;

            // Draw horizontal divider if space enough.
            y += height + mDividerSize;
            if (y < bottom) {
                canvas.drawLine(left, y, right, y, mPaint);
            } else {
                break;
            }
        }

        canvas.restore();
    }
}