利用贝塞尔曲线给UIKit控件加圆角

一般情况下我们给UIKit控件添加圆角都是改变clipsToBounds和layer.cornerRadius,这样虽然看似简单，两行代码就可以搞定。但是，这样使用会强制Core Animation提前渲染屏幕的离屏绘制，而离屏绘制就会为性能带来负面影响。
下面为大家提供一种比较复杂的方式来为控件添加圆角：

#import 

@interface UIView (RoundedCorner)

// 设置顶部圆角
- (void)setRoundedCornerOnTop;

// 设置底部圆角
- (void)setRoundedCornerOnBottom;

// 设置圆角
- (void)setRoundedCorner;

// 取消圆角
- (void)removeRoundedCorner;

// 自定义圆角大小 scale范围：0 ~ 0.5
- (void)setRoundedCornerWithScale:(CGFloat)scale;

// 自定义顶部圆角大小 scale范围：0 ~ 0.5
- (void)setRoundedCornerOnTopWithScale:(CGFloat)scale;

// 自定义底部圆角大小 scale范围：0 ~ 0.5
- (void)setRoundedCornerOnBottomWithScale:(CGFloat)scale;

@end

#import "UIView+RoundedCorner.h"

@implementation UIView (RoundedCorner)

- (void)setRoundedCornerOnTop {
    [self setRoundedCornerOnTopWithScale:0.5];
}

- (void)setRoundedCornerOnBottom {
    [self setRoundedCornerOnBottomWithScale:0.5];
}

- (void)setRoundedCorner {
    [self setRoundedCornerWithScale:0.5];
}

- (void)removeRoundedCorner {
    self.layer.mask = nil;
}

- (void)setRoundedCornerWithScale:(CGFloat)scale {
    if (scale > 0.5) {
        scale = 0.5;
    }
    UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:self.bounds cornerRadius:self.frame.size.height * scale];
    [self setShapeLayer:maskPath];
}

- (void)setRoundedCornerOnTopWithScale:(CGFloat)scale {
    if (scale > 0.5) {
        scale = 0.5;
    }
    UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:self.bounds byRoundingCorners:UIRectCornerTopLeft | UIRectCornerTopRight cornerRadii:CGSizeMake(self.frame.size.height * scale, self.frame.size.height * scale)];
    [self setShapeLayer:maskPath];
}

- (void)setRoundedCornerOnBottomWithScale:(CGFloat)scale {
    if (scale > 0.5) {
        scale = 0.5;
    }
    UIBezierPath *maskPath = [UIBezierPath bezierPathWithRoundedRect:self.bounds byRoundingCorners:UIRectCornerBottomLeft | UIRectCornerBottomRight cornerRadii:CGSizeMake(self.frame.size.height * scale, self.frame.size.height * scale)];
    [self setShapeLayer:maskPath];
}

// 创建CAShapeLayer并设置
- (void)setShapeLayer:(UIBezierPath *)maskPath {
    CAShapeLayer *maskLayer = [CAShapeLayer layer];
    maskLayer.frame = self.bounds;
    maskLayer.path = maskPath.CGPath;
    self.layer.mask = maskLayer;
}

@end

当然还有给UIImageView添加圆角的方法。（注意：如果加载的是网络图片，必须要等网络图片加载完成再调用）

#import 

@interface UIImageView (RoundedCorner)

- (UIImageView *)imageViewWithRoundedCornerSize:(CGFloat)cornerRadius;

@end

#import "UIImageView+RoundedCorner.h"

@implementation UIImageView (RoundedCorner)

- (UIImageView *)imageViewWithRoundedCornerSize:(CGFloat)cornerRadius {
    UIImageView *imageView = self;
    UIImage *original = self.image;
    
    UIGraphicsBeginImageContextWithOptions(imageView.bounds.size, NO, 1.0);
    [[UIBezierPath bezierPathWithRoundedRect:imageView.bounds cornerRadius:cornerRadius] addClip];
    [original drawInRect:imageView.bounds];
    imageView.image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return imageView;
}

@end

代码Demo点这里：http://git.oschina.net/chocklee/RoundedCorner