SPFieldUser is not persistent during postback

If you are using a custom listform and refering to a field of type SPFieldUser. The field tend to loose the content (users) during postback. Some times not easily detected because it will keep the viewstate sometimes.

This has been seen on versions 2007 and 2010.

The fix is relatively simple, by putting the contents into the viewstate in code.

Example:

In the listform.aspx

<SharePoint:FormField runat="server" id="Fld_Present" ControlMode="Edit" FieldName="Present" />

Snippets from codebehind

protected FormField Fld_Present; // Define the field in codebehind

// Define a private String for holding the value during postbacks

 

private String Present

{

    get

    {

        object obj = ViewState["Present"];

        return (obj == null) ? String.Empty : (String)obj;

    }

    set

    {

        ViewState["Present"] = value;

    }

}

 

protected override void CreateChildControls()

        {

            base.CreateChildControls();

 

            if (Fld_Attendees.Value.ToString() != "")

                this.Attendees = Fld_Attendees.Value.ToString();

            else

                Fld_Attendees.Value = new SPFieldUserValueCollection(SPContext.Current.Web, this.Attendees);

 

To keep values when the user field is edited, also add some code before postbacks that is defined in codebehind:

 

if (Fld_Attendees.Value.ToString() != "")

                    this.Attendees = Fld_Attendees.Value.ToString();

 

Convert ListItem ID to UniqueID

This is just one way of getting from the ListItem ID (Not Index) to the GUID UniqueID

In SharePoint 2010 you can use SPList.GetItemByIdSelectedFields(…) or SPList.GetItemByIdAllFields(…)

Example:

GetItemByIdSelectedFields(Int32.Parse(this.ListItemID), new string[] { "UniqueId" });

If you don’t have 2010 you can always retrieve the ListItem with a CAML Query…