小Tips：如何知道有没有离屏渲染Off-Screen Rendering？
Do：通过模拟器->debug->Color Off-screen Rendered，查看UI有没有黄色色块，有就说明是离屏渲染。

离屏渲染的原因有很多，这里不描述，主要说优化性能实现方式。

主要是避免layer.masksToBounds、layer.mask等操作，所以使用贝塞尔曲线UIBezierPath绘制图片、阴影。

基于AFNetworking的网络请求库和相关扩展
CLCornerRadius.h

CLCornerRadius.m代码

#import <AFNetworking/UIKit+AFNetworking.h>

@implementation UIView (CLCornerRadius)

/// 添加阴影效果，带圆角
/// @param color 阴影颜色
/// @param radius 阴影半径
/// @param opacity 阴影不透明度
/// @param offset 阴影偏移量
/// @param cornerRadius 图层圆角
- (void)cl_setShadowColor:(UIColor *)color radius:(CGFloat)radius shadowOpacity:(float)opacity shadowOffset:(CGSize)offset cornerRadius:(CGFloat)cornerRadius {
    // 阴影效果要设置不裁剪
    self.clipsToBounds = NO;
    
    // layer
    self.layer.shadowColor = color.CGColor;
    self.layer.shadowOpacity = opacity;
    self.layer.shadowOffset = offset;
    self.layer.shadowRadius = radius;
    
    // 贝塞尔曲线
    UIBezierPath *bezierPath = [UIBezierPath bezierPathWithRoundedRect:self.bounds cornerRadius:cornerRadius];
    self.layer.shadowPath = bezierPath.CGPath;
    self.layer.cornerRadius = cornerRadius;
}

@end

@implementation UIImage (CLCornerRadius)

/// 绘制图片圆角
/// @param rect 大小
/// @param cornerRadius 圆角
- (UIImage *)cl_drawCornerInRect:(CGRect)rect cornerRadius:(CGFloat)cornerRadius {
    // 开启上下文
    UIGraphicsBeginImageContextWithOptions(rect.size, NO, [UIScreen mainScreen].scale);
    // 使用贝塞尔曲线画出一个圆形图
    [[UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:cornerRadius] addClip];
    // 绘制
    [self drawInRect:rect];
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    // 结束画图
    UIGraphicsEndImageContext();
    return image;
}

@end

@implementation UIImageView (CLCornerRadius)

/// 设置图片，带圆角
/// @param image 图片对象
/// @param cornerRadius 圆角大小
- (void)cl_setImage:(UIImage *)image cornerRadius:(CGFloat)cornerRadius {
    self.image = [image cl_drawCornerInRect:self.bounds cornerRadius:cornerRadius];
}

/// 设置网络图片，带圆角
/// @param urlString 图片地址
/// @param placeholderImage 占位图
/// @param cornerRadius 圆角大小
- (void)cl_setImageUrlString:(NSString *)urlString placeholderImage:(UIImage *)placeholderImage cornerRadius:(CGFloat)cornerRadius {
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlString]];
    [request addValue:@"image/*" forHTTPHeaderField:@"Accept"];
    __weak __typeof(self)weakSelf = self;
    [self setImageWithURLRequest:request placeholderImage:placeholderImage success:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, UIImage * _Nonnull image) {
        [weakSelf cl_setImage:image cornerRadius:cornerRadius];
    } failure:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, NSError * _Nonnull error) {
        [weakSelf cl_setImage:placeholderImage cornerRadius:cornerRadius];
    }];
}

@end

@implementation UIButton (CLCornerRadius)

/// 设置图标，带圆角
/// @param image 图片对象
/// @param cornerRadius 圆角大小
/// @param state 状态
- (void)cl_setImage:(UIImage *)image cornerRadius:(CGFloat)cornerRadius state:(UIControlState)state {
    [self setImage:[image cl_drawCornerInRect:self.bounds cornerRadius:cornerRadius] forState:state];
}

/// 设置图标网络图片，带圆角
/// @param urlString  图片地址
/// @param placeholderImage 占位图
/// @param cornerRadius 圆角大小
/// @param state 状态
- (void)cl_setImageUrlString:(NSString *)urlString placeholderImage:(UIImage *)placeholderImage cornerRadius:(CGFloat)cornerRadius state:(UIControlState)state {
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlString]];
    [request addValue:@"image/*" forHTTPHeaderField:@"Accept"];
    __weak __typeof(self)weakSelf = self;
    [self setBackgroundImageForState:state withURLRequest:request placeholderImage:placeholderImage success:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, UIImage * _Nonnull image) {
        [weakSelf cl_setImage:image cornerRadius:cornerRadius state:state];
        [weakSelf setImage:[image cl_drawCornerInRect:weakSelf.bounds cornerRadius:cornerRadius] forState:state];
    } failure:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, NSError * _Nonnull error) {
        [weakSelf cl_setImage:placeholderImage cornerRadius:cornerRadius state:state];
    }];
}

/// 设置背景图片，带圆角
/// @param image 图片对象
/// @param cornerRadius 圆角大小
/// @param state 状态
- (void)cl_setBackgroundImage:(UIImage *)image cornerRadius:(CGFloat)cornerRadius state:(UIControlState)state {
    [self setBackgroundImage:[image cl_drawCornerInRect:self.bounds cornerRadius:cornerRadius] forState:state];
}

/// 设置网络背景图片，带圆角
/// @param urlString  图片地址
/// @param placeholderImage 占位图
/// @param cornerRadius 圆角大小
/// @param state 状态
- (void)cl_setBackgroundImageUrlString:(NSString *)urlString placeholderImage:(UIImage *)placeholderImage cornerRadius:(CGFloat)cornerRadius state:(UIControlState)state {
    NSMutableURLRequest *request = [NSMutableURLRequest requestWithURL:[NSURL URLWithString:urlString]];
    [request addValue:@"image/*" forHTTPHeaderField:@"Accept"];
    __weak __typeof(self)weakSelf = self;
    [self setBackgroundImageForState:state withURLRequest:request placeholderImage:placeholderImage success:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, UIImage * _Nonnull image) {
        [weakSelf cl_setBackgroundImage:image cornerRadius:cornerRadius state:state];
    } failure:^(NSURLRequest * _Nonnull request, NSHTTPURLResponse * _Nullable response, NSError * _Nonnull error) {
        [weakSelf cl_setBackgroundImage:placeholderImage cornerRadius:cornerRadius state:state];
    }];
}

@end