截取View为图片

+ (UIImage*)snapshot:(UIView *)shotView {   
     UIGraphicsBeginImageContext(shotView.frame.size);   
     UIGraphicsBeginImageContextWithOptions(shotView.frame.size, NO, [[UIScreen mainScreen] scale]);   
     CGContextRef context = UIGraphicsGetCurrentContext(); 
      [shotView.layer renderInContext:context];   
     UIImage *screenShot = UIGraphicsGetImageFromCurrentImageContext();   
     UIGraphicsEndImageContext(); 
     return screenShot;
 }