SharePoint 2010 - Client Object Model - Add attachment to ListItem

I have discussed this question with Microsoft. Looks like that only one way to create attachments remotely is List.asmx web service. I have tried to create this subfolder also and with no success.

I struggled for a long time with this problem too, so I thought I'd post a complete code sample showing how to successfully create a list item and add an attachment.

I am using the Client Object API to create the list item, and the SOAP web service to add the attachment. This is because, as noted in other places on the web, the Client Object API can only be used to add attachments to an item where the item's upload directory already exists (eg. if the item already has an attachment). Else it fails with a 409 error or something. The SOAP web service copes with this OK though.

Note that another thing I had to overcome was that even though I added the SOAP reference using the following URL:

https://my.sharepoint.installation/personal/test/_vti_bin/lists.asmx

The URL that VS actually added to the app.config was:

https://my.sharepoint.installation/_vti_bin/lists.asmx

I had to manually change the app.config back to the correct URL, else I would get the error:

List does not exist. The page you selected contains a list that does not exist. It may have been deleted by another user. 0x82000006

Here is the code:

    void CreateWithAttachment()
    {
        const string listName = "MyListName";
        // set up our credentials
        var credentials = new NetworkCredential("username", "password", "domain");

        // create a soap client
        var soapClient = new ListsService.Lists();
        soapClient.Credentials = credentials;

        // create a client context
        var clientContext = new Microsoft.SharePoint.Client.ClientContext("https://my.sharepoint.installation/personal/test");
        clientContext.Credentials = credentials;

        // create a list item
        var list = clientContext.Web.Lists.GetByTitle(listName);
        var itemCreateInfo = new ListItemCreationInformation();
        var newItem = list.AddItem(itemCreateInfo);

        // set its properties
        newItem["Title"] = "Created from Client API";
        newItem["Status"] = "New";
        newItem["_Comments"] = "here are some comments!!";

        // commit it
        newItem.Update();
        clientContext.ExecuteQuery();

        // load back the created item so its ID field is available for use below
        clientContext.Load(newItem);
        clientContext.ExecuteQuery();

        // use the soap client to add the attachment
        const string path = @"c:\temp\test.txt";
        soapClient.AddAttachment(listName, newItem["ID"].ToString(), Path.GetFileName(path),
                                  System.IO.File.ReadAllBytes(path));
    }

Hope this helps someone.

It reflects rather poorly on the Microsoft SharePoint team for not coming forward with an acknowledgement of the issue and a usable suggestion on how to resolve it. Here is how I dealt with it:

I am using the new SharePoint 2010 managed client that ships with the product. Hence, I already have a SharePoint ClientContext with credentials. The following function adds an attachment to a list item:

private void SharePoint2010AddAttachment(ClientContext ctx, 
                                     string listName, string itemId, 
                                     string fileName, byte[] fileContent)
{
    var listsSvc = new sp2010.Lists();
    listsSvc.Credentials = _sharePointCtx.Credentials;
    listsSvc.Url = _sharePointCtx.Web.Context.Url + "_vti_bin/Lists.asmx";
    listsSvc.AddAttachment(listName, itemId, fileName, fileContent);
}

The only prerequisite for the code above is to add to the project (I used Visual Studio 2008) a _web_reference_ I called sp2010 which is created from the URL of: http:///_vti_bin/Lists.asmx

Bon Chance...

With Sharepoint 2010 there was no way to upload a first attachment to a list item using the COM. The recommendation was to use the Lists web service inmstead.

With Sharepoint 2013 it works.

AttachmentCreationInformation newAtt = new AttachmentCreationInformation();
newAtt.FileName = "myAttachment.txt";
// create a file stream
string fileContent = "This file is was ubloaded by client object meodel ";
System.Text.ASCIIEncoding enc = new System.Text.ASCIIEncoding();
byte[] buffer = enc.GetBytes(fileContent);
newAtt.ContentStream = new MemoryStream(buffer);

// att new item or get existing one
ListItem itm = list.GetItemById(itemId);
ctx.Load(itm);   
// do not execute query, otherwise a "version conflict" exception is rised, but the file         is uploaded
// add file to attachment collection
newAtt.ContentStream = new MemoryStream(buffer);
itm.AttachmentFiles.Add(newAtt); 
AttachmentCollection attachments = itm.AttachmentFiles;
ctx.Load(attachments);
ctx.ExecuteQuery(); 
// see all attachments for list item
// this snippet works if the list item has no attachments

This method is used in http://www.mailtosharepoint.net/