根據圖片的寬高比例設置imageView的size

配合SDWebImage

-(CGSize )sizeWithImageUrlString:(NSString *)imageurl width:(CGFloat) width
{
    CGFloat itemW = width;
    CGFloat itemH = 0;
    UIImageView * imageView = [[UIImageView alloc] init];
    NSURL * url = [NSURL URLWithString:imageurl];
    [imageView sd_setImageWithURL:url placeholderImage:nil];
    SDWebImageManager *manager = [SDWebImageManager sharedManager];
    BOOL existBool = [manager diskImageExistsForURL:url];//判斷是否有緩存
    UIImage * image;
    if (existBool) {
        image = [[manager imageCache] imageFromDiskCacheForKey:url.absoluteString];
    }else{
        NSData *data = [NSData dataWithContentsOfURL:url];
        image = [UIImage imageWithData:data];
    }

    //根據image的比例來設置高度
    if (image.size.width) {
        itemH = image.size.height / image.size.width * itemW;
    }

    return CGSizeMake(itemW, itemH);
}