我做了一个小小的实验，

Future<String> getFinalizedDoc() async{
var jsonPost = jsonDecode(widget.post);
for (var operation in jsonPost){
  if (operation['insert'] is Map && operation['insert'].containsKey('image') && operation['insert']['image'] != "" && !Uri.parse(operation['insert']['image']).isAbsolute) {
    String oldImagePath = await operation['insert']['image'];
    operation['insert']['image'] = await uploadAssetsToStore(
      filePath: File(oldImagePath),
      folderName: 'PostImages',
      fileName: path_delegate.basename(oldImagePath)
    );
  }
  else if (operation['insert'] is Map && operation['insert'].containsKey('video') && operation['insert']['video'] != "" && !Uri.parse(operation['insert']['video']).isAbsolute) {
    String oldVideoPath = await operation['insert']['video'];
    operation['insert']['video'] = await uploadAssetsToStore(
        filePath: File(oldVideoPath),
        folderName: 'PostVideos',
        fileName: path_delegate.basename(oldVideoPath)
    );
  }
}
return jsonEncode(jsonPost);

}