ColorDividerItemDecoration for RecyclerView

ColorDividerItemDecoration.java

public final class ColorDividerItemDecoration extends RecyclerView.ItemDecoration {
  private static final int DEFAULT_DIVIDER_COLOR = Color.GRAY;
  private static final int DEFAULT_DIVIDER_SIZE_PX = 1;
  private static final boolean DEFAULT_DIVIDER_SHOW_FIRST = false;
  private static final boolean DEFAULT_DIVIDER_SHOW_LAST = false;

  private final boolean showFirstDivider;
  private final boolean showLastDivider;
  private final Paint paint;

  public ColorDividerItemDecoration() {
    this(DEFAULT_DIVIDER_COLOR, DEFAULT_DIVIDER_SIZE_PX, DEFAULT_DIVIDER_SHOW_FIRST, DEFAULT_DIVIDER_SHOW_LAST);
  }

  public ColorDividerItemDecoration(@ColorInt int color) {
    this(color, DEFAULT_DIVIDER_SIZE_PX, DEFAULT_DIVIDER_SHOW_FIRST, DEFAULT_DIVIDER_SHOW_LAST);
  }

  public ColorDividerItemDecoration(@ColorInt int color, int sizePx) {
    this(color, sizePx, DEFAULT_DIVIDER_SHOW_FIRST, DEFAULT_DIVIDER_SHOW_LAST);
  }

  public ColorDividerItemDecoration(@ColorInt int color, int sizePx, boolean showFirstDivider, boolean showLastDivider) {
    paint = new Paint();
    paint.setColor(color);
    paint.setStrokeWidth(sizePx);

    this.showFirstDivider = showFirstDivider;
    this.showLastDivider = showLastDivider;
  }

  @Override public void onDrawOver(Canvas canvas, RecyclerView parent, RecyclerView.State state) {
    float left = parent.getPaddingLeft();
    float right = parent.getWidth() - parent.getPaddingRight();
    float top = parent.getPaddingTop();
    float bottom = parent.getHeight() - parent.getPaddingBottom();

    int orientation = getOrientation(parent);
    int childCount = parent.getChildCount();

    for (int i = 0; i < childCount; i++) {
      View child = parent.getChildAt(i);
      RecyclerView.LayoutParams params = (RecyclerView.LayoutParams) child.getLayoutParams();

      if ((showFirstDivider && i == 0) || i > 0) {
        if (orientation == LinearLayoutManager.VERTICAL) {
          top = child.getTop() - params.topMargin;
          bottom = top - (paint.getStrokeWidth() / 2);

          canvas.drawLine(left, bottom, right, bottom, paint);
        } else {
          left = child.getLeft() - params.leftMargin;
          right = left - (paint.getStrokeWidth() / 2);

          canvas.drawLine(right, top, right, bottom, paint);
        }
      }

      if (showLastDivider && i == childCount - 1) {
        if (orientation == LinearLayoutManager.VERTICAL) {
          top = child.getBottom() - params.bottomMargin;
          bottom = top + (paint.getStrokeWidth() / 2);

          canvas.drawLine(left, bottom, right, bottom, paint);
        } else {
          left = child.getRight() + params.rightMargin;
          right = left + (paint.getStrokeWidth() / 2);

          canvas.drawLine(right, top, right, bottom, paint);
        }
      }
    }
  }

  private int getOrientation(RecyclerView parent) {
    if (parent.getLayoutManager() instanceof LinearLayoutManager) {
      LinearLayoutManager layoutManager = (LinearLayoutManager) parent.getLayoutManager();
      return layoutManager.getOrientation();
    } else {
      throw new IllegalStateException("ColorDividerItemDecoration can only be used with a LinearLayoutManager.");
    }
  }
}

RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
recyclerView.addItemDecoration(new ColorDividerItemDecoration());