SDWebImage是如何做到Url不变的情况下，更新图片内容

需要做如下处理：在APPdelegate的didFinishLaunchingWithOptions方法中添加如下对SDWebImage的配置

- (void)SDWebImageSetup {

// SDWebImage 缓存配置

SDWebImageDownloader *imgDownloader = SDWebImageManager.sharedManager.imageDownloader;

// 获取SDWebImage的下载对象，所有图片的下载都是此对象完成的 SDWebImageDownloader *imgDownloader = SDWebImageManager.sharedManager.imageDownloader;

imgDownloader.headersFilter  = ^NSDictionary *(NSURL *url, NSDictionary *headers) {

// 下载图片成功后的回调

NSFileManager *fm = [[NSFileManager alloc] init];

NSString *imgKey = [SDWebImageManager.sharedManager cacheKeyForURL:url];

NSString *imgPath = [SDWebImageManager.sharedManager.imageCache defaultCachePathForKey:imgKey];

// 获取当前路径图片服务端返回的请求头相关信息

NSDictionary *fileAttr = [fm attributesOfItemAtPath:imgPath error:nil];

NSMutableDictionary *mutableHeaders = [headers mutableCopy];

NSDate *lastModifiedDate = nil;

// 大于0则表示请求图片成功

if (fileAttr.count > 0) {

if (fileAttr.count > 0) {

// 如果请求成功，则手机端取出服务端Last-Modified信息

lastModifiedDate = (NSDate *)fileAttr[NSFileModificationDate];

}

}

// 格式化Last-Modified

NSDateFormatter *formatter = [[NSDateFormatter alloc] init];

formatter.timeZone = [NSTimeZone timeZoneWithAbbreviation:@"GMT"];

formatter.locale = [[NSLocale alloc] initWithLocaleIdentifier:@"en_US"];

formatter.dateFormat = @"EEE, dd MMM yyyy HH:mm:ss z";

NSString *lastModifiedStr = [formatter stringFromDate:lastModifiedDate];

lastModifiedStr = lastModifiedStr.length > 0 ? lastModifiedStr : @"";

// 设置SDWebImage的请求头If-Modified-Since

[mutableHeaders setValue:lastModifiedStr forKey:@"If-Modified-Since"];

return mutableHeaders;

};

}

在需要使用的地方，对imageView进行SDWebImageRefreshCached操作，如：[_headerpicView sd_setImageWithURL:[NSURL URLWithString:[NSString stringWithFormat:@"%@", self.userinfodict[@"userpic"]]] placeholderImage:[UIImage imageNamed:@"my_head_default"] options:SDWebImageRefreshCached];