Android Dibujando un separador


Ejemplo

Esto dibujará una línea en la parte inferior de cada vista, pero la última en actuar como un separador entre los elementos.

public class SeparatorDecoration extends RecyclerView.ItemDecoration {

    private final Paint mPaint;
    private final int mAlpha;

    public SeparatorDecoration(@ColorInt int color, float width) {
        mPaint = new Paint();
        mPaint.setColor(color);
        mPaint.setStrokeWidth(width);
        mAlpha = mPaint.getAlpha();
    }

    @Override
    public void getItemOffsets(Rect outRect, View view, RecyclerView parent, RecyclerView.State state) {
        final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) view.getLayoutParams();

        // we retrieve the position in the list
        final int position = params.getViewAdapterPosition();

        // add space for the separator to the bottom of every view but the last one
        if (position < state.getItemCount()) {
            outRect.set(0, 0, 0, (int) mPaint.getStrokeWidth()); // left, top, right, bottom
        } else {
            outRect.setEmpty(); // 0, 0, 0, 0
        }
    }

    @Override
    public void onDraw(Canvas c, RecyclerView parent, RecyclerView.State state) {
        // a line will draw half its size to top and bottom,
        // hence the offset to place it correctly
        final int offset = (int) (mPaint.getStrokeWidth() / 2);

        // this will iterate over every visible view
        for (int i = 0; i < parent.getChildCount(); i++) {
            final View view = parent.getChildAt(i);
            final RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) view.getLayoutParams();

            // get the position
            final int position = params.getViewAdapterPosition();

            // and finally draw the separator
            if (position < state.getItemCount()) {
                // apply alpha to support animations
                mPaint.setAlpha((int) (view.getAlpha() * mAlpha));

                float positionY = view.getBottom() + offset + view.getTranslationY();
                // do the drawing
                c.drawLine(view.getLeft() + view.getTranslationX(),
                        positionY,
                        view.getRight() + view.getTranslationX(),
                        positionY,
                        mPaint);
            }
        }
    }
}