Snip20180131_3.png

让带有圆角的空间有阴影，有两种方法

方法一：用一个透明的view作为这个圆角控件的父控件

Snip20180131_4.png
具体就是让父控件的背景颜色为clearColor，再设置父控件的阴影颜色。圆角控件只需要切圆角就好了。

    self.rectangleView.layer.cornerRadius = 20;
    self.rectangleView.layer.masksToBounds = YES;
    
    self.recBGView.backgroundColor = [UIColor clearColor];
    self.recBGView.layer.shadowColor = [UIColor redColor].CGColor;
    self.recBGView.layer.shadowOffset = CGSizeZero;
    self.recBGView.layer.shadowOpacity = 1;

方法二，设置控件的shadowPath

第二种方法要自定义控件，因为路径要在- (void)drawRect:(CGRect)rect方法里面绘制才有效

- (void)drawRect:(CGRect)rect {
    // Drawing code
// 这个阴影路径可以自己画，灵活很多
    UIBezierPath *recPath = [UIBezierPath bezierPathWithRoundedRect:self.recView.bounds cornerRadius:50];
    self.recView.layer.shadowPath = recPath.CGPath;
}

- (instancetype)initWithFrame:(CGRect)frame
{
    self = [super initWithFrame:frame];
    if (self) {
        self.backgroundColor = [UIColor clearColor];
        UIView *recView = [[UIView alloc] initWithFrame:CGRectMake(self.frame.size.width / 2 - 50, 30, 100, 100)];
        recView.backgroundColor = [UIColor whiteColor];
        recView.layer.shadowOpacity = 1;
        recView.layer.shadowColor = [UIColor redColor].CGColor;
        recView.layer.cornerRadius = 50;
        [self addSubview:recView];
        self.recView = recView;
    }
    return self;
}