自定义网络请求图片的大小

NSURL *url = [NSURL URLWithString:[[self.imageSource objectAtIndex:indexPath.section] objectAtIndex:indexPath.row]];

        UIImage *icon = [UIImage imageWithData:[NSData dataWithContentsOfURL:url]];

        CGSize itemSize = CGSizeMake(30, 30);

        UIGraphicsBeginImageContextWithOptions(itemSize, NO,0.0);

        CGRect imageRect = CGRectMake(0.0, 0.0, itemSize.width, itemSize.height);

        [icon drawInRect:imageRect];

        cell.imageView.image = UIGraphicsGetImageFromCurrentImageContext();

        UIGraphicsEndImageContext();