iOS WebView中使用webp格式图片的方法

@try {
 HTMLParser *parser = [[HTMLParser alloc] initWithString:htmlContent error:&error];
 HTMLNode *bodyNode = [parser body];
 if (error) {
 return;
 }
 //得到所有的img标签
 NSArray *inputNodes = [bodyNode findChildTags:@"img"];

 for (HTMLNode *inputNode in inputNodes) {
 NSString *imageSrc = [inputNode getAttributeNamed:@"src"];
 if (!imageSrc) {
  continue;
 }
 NSString *newSrc = [[GlobalVariable shareInstance] resizeWebpImageWithUrl:imageSrc size:CGSizeMake((SCREEN_WIDTH - 20) * 2, 0)];//根据原图片，得到webp服务器使用的图片链接，需要有webp处理服务器
 //检查本地图片缓存
 NSString *key = [[SDWebImageManager sharedManager] cacheKeyForURL:[NSURL URLWithString:newSrc]];
 NSString *localPath = [[SDImageCache sharedImageCache] defaultCachePathForKey:key];
 NSString *webpImage = newSrc;
 BOOL localExsit = [[NSFileManager defaultManager] fileExistsAtPath:localPath];
 if (localExsit) {
  newSrc = [NSString stringWithFormat:@"file://%@", localPath];
 }
 //存储疑似webp图片和原图片，如果newSrc和webp相同则说明本地没有缓存图片
 [_webpImageUrlDic setObject:webpImage forKey:newSrc];
 if(localExsit){
  setAttributeNamed(inputNode->_node, "src", [newSrc cStringUsingEncoding:NSUTF8StringEncoding]);
 }else{
  setAttributeNamed(inputNode->_node, "src", "详情页占位图@2x.png");
 }
 //给img标签中增加一个叫osrc的属性，便于后续处理
 setAttributeNamed(inputNode->_node, "osrc", [newSrc cStringUsingEncoding:NSUTF8StringEncoding]);
 }
 htmlContent = [NSMutableString stringWithString:parser.doc.rawContents];
}
@catch (NSException *exception) {
}
@finally {
 [webView loadHTMLString:htmlContent baseURL:baseUrl];
}

- (void)webViewDidFinishLoad:(UIWebView *)web {
 //处理webp格式加载
 [_webpImageUrlDic enumerateKeysAndObjectsUsingBlock:^(id _Nonnull key, id _Nonnull obj, BOOL * _Nonnull stop) {
 if([obj isEqualToString:key]){//说明这图没有缓存，还需要下载
  [[SDWebImageDownloader sharedDownloader] downloadImageWithURL:[NSURL URLWithString:obj] options:0 progress:nil completed:^(UIImage *image, NSData *data, NSError *error, BOOL finished) {
  if (image&&finished) {
   NSString *js;
   NSRange range = [[obj lowercaseString] rangeOfString:@".gif"];//检查是否是gif
   BOOL isGif = (range.location != NSNotFound);
   if (!isGif) {
   [[SDImageCache sharedImageCache] storeImage:image forKey:obj];
   NSString *base64 = [UIImageJPEGRepresentation(image,1) base64EncodedStringWithOptions:0];
   js = [NSString stringWithFormat:@"replaceWebPImg('%@','data:image/jpeg;base64,%@')",key,base64];
   }else{//gif的图片如果直接存储，会变成jpg从而失去动画，因此要特殊处理
   [[SDImageCache sharedImageCache] storeImage:image recalculateFromImage:false imageData:data forKey:key toDisk:true];
   NSString *base64 = [data base64EncodedStringWithOptions:0];
   js = [NSString stringWithFormat:@"replaceWebPImg('%@','data:image/gif;base64,%@')",key,base64];
   }
   [NSThread excuteInMainThread:^{
   [webView stringByEvaluatingJavaScriptFromString:js];
   } async:false];
  }
  }];
 } else {//缓存中存在，那么直接加载吧
  NSString *js;
  NSRange range = [[obj lowercaseString] rangeOfString:@".gif"];//检查是否是gif
  NSData* data = [NSData dataWithContentsOfFile:[key stringByReplacingOccurrencesOfString:@"file://" withString:@""]];
  NSString *base64 = [data base64EncodedStringWithOptions:0];
  BOOL isGif = (range.location != NSNotFound);
  if (!isGif) {
  js = [NSString stringWithFormat:@"replaceWebPImg('%@','data:image/jpeg;base64,%@')",obj,base64];
  }else{
  js = [NSString stringWithFormat:@"replaceWebPImg('%@','data:image/gif;base64,%@')",obj,base64];
  }
  [NSThread excuteInMainThread:^{
  [webView stringByEvaluatingJavaScriptFromString:js];
  } async:false];
 }
 }];
} 

replaceWebPImg = function(src, localPath) {
 var imgs = document.querySelectorAll('img[osrc="'+src+'"]'),len = imgs.length;;
 for (var i = 0; i < len; i++) {
 var img = imgs[i];
 img.src = localPath;
 }
}