iOS 圆角 阴影

static dispatch_once_t onceToken;
    dispatch_once(&onceToken, ^{
        CALayer *layer = [CALayer layer];
        layer.name = @"shadow";
        layer.frame = self.containerView.frame;
        layer.backgroundColor = [UIColor whiteColor].CGColor;
        layer.shadowOffset = CGSizeZero;
        layer.shadowColor = [[UIColor lightGrayColor] CGColor];
        layer.shadowOpacity = 0.8;
        layer.shadowRadius = 6;
        layer.cornerRadius = 20;
        [self.view.layer insertSublayer:layer atIndex:0];
        self.shadow = layer;
    });