圆角原理：设置view.layer.mask该遮罩层。

圆角边框：在view.layer 上增加一层，绘制圆角边框。
有个问题注意：
使用CAShapeLayer绘制边框圆角边框
设置边框的颜色 ：
strokeColor 设置其值，并且同时要设置fillColor为clearColor. 这样才会绘制边框。不然会全部绘制。内容就被遮挡了。

圆角和圆角边框

示例代码如下：

- (void)viewDidLoad {
    [super viewDidLoad];
    // Do any additional setup after loading the view.
   self.view.backgroundColor = [UIColor whiteColor];
    
    UIView *view = [UIView new];
    view.frame = CGRectMake(100, 200, 120, 30);
    view.backgroundColor = [UIColor redColor];
    [self.view addSubview:view];
    
    //设置view的左上和右下为圆角
    [self setCornerWithView:view viewSize:view.frame.size corners:(UIRectCornerTopLeft|UIRectCornerBottomRight) radius:10];
    
    UILabel *lable = [UILabel new];
    lable.frame = CGRectMake(100, 300, 120, 30);
    lable.font = [UIFont systemFontOfSize:14];
    lable.textAlignment = NSTextAlignmentCenter;
    lable.text = @"看我的圆角边框";
    [self.view addSubview:lable];
    
    //绘制label边框,左下和右上为圆角
    [self setCornerWithView:lable viewSize:lable.frame.size corners:(UIRectCornerBottomLeft|UIRectCornerTopRight) radius:10 borderColor:[UIColor blackColor]];
}

#pragma mark - 设置View任意角为圆角

/// 设置View任意角度为圆角
/// @param view 待设置的view
/// @param viewSize view的size
/// @param corners 设置的角，左上、左下、右上、右下，可以组合
/// 如左下和右上 (UIRectCornerBottomLeft | UIRectCornerTopRight)
/// @param radius 圆角的半径
- (void)setCornerWithView:(UIView*)view
                 viewSize:(CGSize)viewSize
                  corners:(UIRectCorner)corners
                   radius:(CGFloat)radius{
    CGRect fr = CGRectZero;
    fr.size = viewSize;
    
    UIBezierPath *round = [UIBezierPath bezierPathWithRoundedRect:fr byRoundingCorners:corners cornerRadii:CGSizeMake(radius, radius)];
    
    CAShapeLayer *shape = [[CAShapeLayer alloc]init];
    
    [shape setPath:round.CGPath];
    view.layer.mask = shape;
}

/// 绘制view的圆角边框, 只是在view上画了一个圆角边框，并不会裁剪view
/// @param view 待设置的view
/// @param viewSize view的size
/// @param corners 设置的角，左上、左下、右上、右下，可以组合
/// 如左下和右上 (UIRectCornerBottomLeft | UIRectCornerTopRight)
/// @param radius 圆角的半径
/// @param borderColor 边框颜色
- (void)setCornerWithView:(UIView*)view
                 viewSize:(CGSize)viewSize
                  corners:(UIRectCorner)corners
                   radius:(CGFloat)radius
              borderColor:(UIColor*)borderColor{
    CGRect fr = CGRectZero;
    fr.size = viewSize;
    
    UIBezierPath *round = [UIBezierPath bezierPathWithRoundedRect:fr byRoundingCorners:corners cornerRadii:CGSizeMake(radius, radius)];
    
    CAShapeLayer *shape = [[CAShapeLayer alloc]init];
    
    [shape setPath:round.CGPath];
    shape.strokeColor = borderColor.CGColor;
    shape.fillColor = [UIColor clearColor].CGColor;
    [view.layer addSublayer:shape];
}