分析原因：因为代码中设置了masksToBounds属性为YES了，将后面设置的阴影效果给裁剪掉了，所以我们看不到阴影效果，如果我们将masksToBounds属性为NO了，这样就会失去圆角效果
解决方案：给imageView添加一个父视图，在父视图上添加阴影效果就好，这样就不会对imageView的圆角造成影响了
实例代码：UIImageView*imgView = [[UIImageViewalloc]initWithFrame:CGRectMake(0,0,150,200)];
imgView.layer.masksToBounds = YES;
imgView.layer.cornerRadius=20;
imgView.backgroundColor = [UIColor whiteColor];
UIView*shadowView = [[UIViewalloc]initWithFrame:CGRectMake(200,200,150,200)];
[self.viewaddSubview:shadowView];
shadowView.layer.shadowColor = [UIColor blackColor].CGColor;
shadowView.layer.shadowOffset = CGSizeMake(0, 2);
shadowView.layer.shadowOpacity=0.2;
shadowView.layer.shadowRadius=3.0;
shadowView.layer.cornerRadius=3.0;
shadowView.clipsToBounds=NO;
[shadowViewaddSubview:imgView];
效果截图：
