How to upload an attachment to a list item using Microsoft.SharePoint.Client?

Question

I am trying to create a new list item with an attachment. Below is my code:

using (var clientContext = new ClientContext(_sharepointSiteURL))
{
   clientContext.Credentials = _credentials;
   var list = clientContext.Web.Lists.GetByTitle("ListName");
   var listEntry = list.AddItem(new ListItemCreationInformation());
   listEntry["Title"] = model.Title;
   listEntry.Update();
   clientContext.ExecuteQuery();
   var attInfo = new AttachmentCreationInformation();
   attInfo.ContentStream = model.File.InputStream;
   attInfo.FileName = model.File.FileName;
   var attachment = listEntry.AttachmentFiles.Add(attInfo);
   clientContext.Load(attachment);
   clientContext.ExecuteQuery();
}

The list item creation code works fine but the file attachment code throws the following error:

Microsoft.SharePoint.Client.ServerException: Data at the root level is invalid. Line 2, position 1.

on the last clientContext.ExecuteQuery().

Does anyone have any ideas as to what the cause of this is?

Answer 1

I was having this same error while uploading a PDF to SharePoint.

Solved it by using the Microsoft.SharePoint.Client.File.SaveBinaryDirect() method instead.

Read how to Upload large files sample app for SharePoint