原文链接:http://www.cnblogs.com/Walking-Jin/p/5754519.html

定义方法

/** 取消searchBar背景色 */ 
- (UIImage *)imageWithColor:(UIColor *)color size:(CGSize)size
{
    CGRect rect = CGRectMake(0, 0, size.width, size.height);
    UIGraphicsBeginImageContext(rect.size);
    CGContextRef context = UIGraphicsGetCurrentContext();
    
    CGContextSetFillColorWithColor(context, [color CGColor]);
    CGContextFillRect(context, rect);
    
    UIImage *image = UIGraphicsGetImageFromCurrentImageContext();
    UIGraphicsEndImageContext();
    
    return image;
}

调用

_searchBar.backgroundImage = [self imageWithColor:[UIColor clearColor] size:_searchBar.bounds.size];