- (UIView *)arrowView{
    if (!_arrowView) {
        // draw
        CGSize size = CGSizeMake(kDefaultArrowWeight, kDefaultArrowHeight);
        UIBezierPath *path = [[UIBezierPath alloc] init];
        [path moveToPoint:CGPointMake(size.width / 2.0, 0)];
        [path addLineToPoint:CGPointMake(0, size.height)];
        [path addLineToPoint:CGPointMake(size.width, size.height)];
        path.lineWidth = 1.0;
        
        CAShapeLayer *arrowLayer = [CAShapeLayer layer];
        arrowLayer.path = path.CGPath;
        
        _arrowView = [[UIView alloc] initWithFrame:CGRectMake(0, 0, size.width, size.height)];
        _arrowView.layer.mask = arrowLayer;
        _arrowView.backgroundColor = self.contentViewBackgroundColor;
    }
    return _arrowView;
}