我写了这个UIView分类方法来解决这个问题，使用单独的视图来表示阴影和角的半径。

-(UIView *)shadowedWrapViewWithBounds:(CGRect)bounds {
UIView *baseView = [[UIView alloc] init];
baseView.bounds = bounds;
baseView.backgroundColor = [UIColor clearColor];
baseView.layer.shadowColor = [UIColor blackColor].CGColor;
baseView.layer.shadowOffset = CGSizeMake(0, 0);
baseView.layer.shadowOpacity = 0.7;
baseView.layer.shadowRadius = 4.0;

// improve performance
baseView.layer.shadowPath = [UIBezierPath bezierPathWithRoundedRect:baseView.bounds cornerRadius:4].CGPath;
baseView.layer.shouldRasterize = YES;
baseView.layer.rasterizationScale = [UIScreen mainScreen].scale;

[baseView addSubview:self];
//use Masonry autolayout, self can set corner radius
[self makeConstraints:^(MASConstraintMaker *make) {
    make.edges.equalTo(baseView);
}];

return baseView;
}

我在UIView中创建了一个helper

@interface UIView (Helper)

- (void)roundCornerswithRadius:(float)cornerRadius
               andShadowOffset:(float)shadowOffset;
@end

你可以这样叫它

[self.view roundCornerswithRadius:5 andShadowOffset:5];

这是实现

- (void)roundCornerswithRadius:(float)cornerRadius
               andShadowOffset:(float)shadowOffset
{
    const float CORNER_RADIUS = cornerRadius;
    const float SHADOW_OFFSET = shadowOffset;
    const float SHADOW_OPACITY = 0.5;
    const float SHADOW_RADIUS = 3.0;

    UIView *superView = self.superview;

    CGRect oldBackgroundFrame = self.frame;
    [self removeFromSuperview];

    CGRect frameForShadowView = CGRectMake(0, 0, oldBackgroundFrame.size.width, oldBackgroundFrame.size.height);
    UIView *shadowView = [[UIView alloc] initWithFrame:frameForShadowView];
    [shadowView.layer setShadowOpacity:SHADOW_OPACITY];
    [shadowView.layer setShadowRadius:SHADOW_RADIUS];
    [shadowView.layer setShadowOffset:CGSizeMake(SHADOW_OFFSET, SHADOW_OFFSET)];

    [self.layer setCornerRadius:CORNER_RADIUS];
    [self.layer setMasksToBounds:YES];

    [shadowView addSubview:self];
    [superView addSubview:shadowView];

}

我尝试了这篇文章中的很多解决方案，最终得到了下面的解决方案。这是完全证明解决方案，除非你需要在一个清晰的颜色视图下滴阴影。

- (void)addShadowWithRadius:(CGFloat)shadowRadius withOpacity:(CGFloat)shadowOpacity withOffset:(CGSize)shadowOffset withColor:(UIColor *)shadowColor withCornerradius:(CGFloat)cornerRadius
{
    UIView *viewShadow = [[UIView alloc]initWithFrame:self.frame];
    viewShadow.backgroundColor = [UIColor whiteColor];
    viewShadow.layer.shadowColor = shadowColor.CGColor;
    viewShadow.layer.shadowOffset = shadowOffset;
    viewShadow.layer.shadowRadius = shadowRadius;
    viewShadow.layer.shadowOpacity = shadowOpacity;
    viewShadow.layer.cornerRadius = cornerRadius;
    viewShadow.layer.masksToBounds = NO;
    [self.superview insertSubview:viewShadow belowSubview:self];

    [viewShadow setTranslatesAutoresizingMaskIntoConstraints:NO];
    [self.superview addConstraint:[NSLayoutConstraint constraintWithItem:viewShadow attribute:NSLayoutAttributeWidth relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeWidth multiplier:1.0 constant:0]];
    [self.superview addConstraint:[NSLayoutConstraint constraintWithItem:viewShadow attribute:NSLayoutAttributeHeight relatedBy:NSLayoutRelationEqual toItem:self attribute:NSLayoutAttributeHeight multiplier:1.0 constant:0]];
    [self.superview addConstraint:[NSLayoutConstraint constraintWithItem:viewShadow attribute:NSLayoutAttributeCenterX relatedBy:NSLayoutRelationEqual toItem:viewShadow attribute:NSLayoutAttributeCenterX multiplier:1.0 constant:0]];
    [self.superview addConstraint:[NSLayoutConstraint constraintWithItem:viewShadow attribute:NSLayoutAttributeCenterY relatedBy:NSLayoutRelationEqual toItem:viewShadow attribute:NSLayoutAttributeCenterY multiplier:1.0 constant:0]];
    [self layoutIfNeeded];

    self.layer.cornerRadius = cornerRadius;
    self.layer.masksToBounds = YES;
}

var shadows = UIView()
shadows.frame = view.frame
shadows.clipsToBounds = false
view.addSubview(shadows)


let shadowPath0 = UIBezierPath(roundedRect: shadows.bounds, cornerRadius: 10)
let layer0 = CALayer()
layer0.shadowPath = shadowPath0.cgPath
layer0.shadowColor = UIColor(red: 0, green: 0, blue: 0, alpha: 0.23).cgColor
layer0.shadowOpacity = 1
layer0.shadowRadius = 6
layer0.shadowOffset = CGSize(width: 0, height: 3)
layer0.bounds = shadows.bounds
layer0.position = shadows.center

shadows.layer.addSublayer(layer0)

Evan Mulawski提供的答案将会非常有效。问题是你必须将视图的背景色设置为clearColor，并将masksToBounds属性设置为NO。

你可以为视图设置任何你想要的颜色

v.layer.backgroundColor = your color;

希望这能有所帮助。

你需要使用两个uiview来实现这一点。一个UIView会像阴影一样工作，另一个会为圆角边界工作。

下面是一个在协议帮助下的类方法的代码片段:

@implementation UIMethods

+ (UIView *)genComposeButton:(UIViewController <UIComposeButtonDelegate> *)observer;
{
    UIView *shadow = [[UIView alloc]init];
    shadow.layer.cornerRadius = 5.0;
    shadow.layer.shadowColor = [[UIColor blackColor] CGColor];
    shadow.layer.shadowOpacity = 1.0;
    shadow.layer.shadowRadius = 10.0;
    shadow.layer.shadowOffset = CGSizeMake(0.0f, -0.5f);

    UIButton *btnCompose = [[UIButton alloc]initWithFrame:CGRectMake(0, 0,60, 60)];
    [btnCompose setUserInteractionEnabled:YES];
    btnCompose.layer.cornerRadius = 30;
    btnCompose.layer.masksToBounds = YES;
    [btnCompose setImage:[UIImage imageNamed:@"60x60"] forState:UIControlStateNormal];
    [btnCompose addTarget:observer action:@selector(btnCompose_click:) forControlEvents:UIControlEventTouchUpInside];
    [shadow addSubview:btnCompose];
    return shadow;
}

在上面的代码中，btnCompose_click:将成为一个@required委托方法，该方法将在单击按钮时触发。

在这里我添加了一个按钮到我的UIViewController，像这样:

UIView *btnCompose = [UIMethods genComposeButton:self];
btnCompose.frame = CGRectMake(self.view.frame.size.width - 75,
                          self.view.frame.size.height - 75,
                          60, 60);
[self.view addSubview:btnCompose];

结果如下所示: