最直接的方法就是使用如下屬性設置：

imgView.layer.cornerRadius = 10;
// 這一行代碼是很消耗性能的
imgView.clipsToBounds = YES;

這是離屏渲染（off-screen-rendering），消耗性能的
給UIImage添加生成圓角圖片的擴展API：這是on-screen-rendering

- (UIImage *)imageWithCornerRadius:(CGFloat)radius {
CGRect rect = (CGRect){0.f, 0.f, self.size};
 
UIGraphicsBeginImageContextWithOptions(self.size, NO, UIScreen.mainScreen.scale);
CGContextAddPath(UIGraphicsGetCurrentContext(),
 [UIBezierPath bezierPathWithRoundedRect:rect cornerRadius:radius].CGPath);
CGContextClip(UIGraphicsGetCurrentContext());
 
[self drawInRect:rect];
UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
 
UIGraphicsEndImageContext();
 
return image;
}