###修改图片为圆形

方法1: 修改UIImageView的layer

    imageView.layer.cornerRadius = self.size.width/2;
    imageView.clipsToBounds = YES;

方法2: 裁剪image

#import "UIImage+SRExtension.h"

@implementation UIImage (SRExtension)


-(UIImage *)circleImage{

    // NO:代表透明
    UIGraphicsBeginImageContextWithOptions(self.size, NO, 0.0);
    
    //获取图片上下文
    CGContextRef ref = UIGraphicsGetCurrentContext();
    
    //添加一个园
    CGRect rect = CGRectMake(0, 0, self.size.width,self.size.height);

    CGContextAddEllipseInRect(ref, rect);
    
    //裁剪
    CGContextClip(ref);
    
    
    //画上去
    [self drawInRect:rect];
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    
    UIGraphicsEndImageContext();

    return image;
}