ItemUpdated event handler runs four times

Question

I have a list in the rootweb, and a list in a subweb. I want to update/add when something changes in an item in the subweb. This method is invoked in an ItemUpdated event receiver. The problem is that the item is added four times to the rootlist.

/// <summary>
/// Updates an item on a rootweblist, or adds the item if it doesn't exist.
/// </summary>
/// <param name="leafWeb">The web the updated item belongs to</param>
/// <param name="leafItem">The item being updated</param>
/// <param name="rootWebListName">The name of the list in the root web</param>
/// <param name="contentTypeName">Name of the custom content type</param>
/// <param name="fieldsToUpdate">The fields to update</param>
internal void UpdateItemOnRootwebList(SPWeb leafWeb, SPListItem leafItem, string rootWebListName, string contentTypeName, List<string> fieldsToUpdate)
{
    //Impersonate system account - Not sure if needed
    var systemAccToken = leafWeb.Site.SystemAccount.UserToken;
    using (var kundeSiteCol = new SPSite(leafWeb.Site.ID, systemAccToken))
    {
        using (var rootWeb = kundeSiteCol.OpenWeb())
        {
            var rootList = rootWeb.Lists.TryGetList(rootWebListName);
            if (rootList != null)
            {
                //Find the corresponding item on rootlist, or create a new if it doesn't exist
                var listItems = rootList.Items;
                var rootItem = listItems.Cast<SPItem>().FirstOrDefault(and => and["Title"] == leafItem["Title"]);
                if (rootItem == null) rootItem = listItems.Add();

                //Set content type
                var itemType = rootList.ContentTypes[contentTypeName];
                rootItem["ContentTypeId"] = itemType.Id;

                //Update the relevant fields
                foreach (var field in fieldsToUpdate)
                {
                    rootItem[field] = leafItem[field];
                }
                //Update the item, or add if it doesn't exist
                rootItem.Update();
            }
        }
    }
}

Update: Rephrased the question tremendously.

Answer 1

I anticipate that your root list has the same event receiver assigned to it, and that causes the recursion.

The problem, of course, may be not so obvious, but anyway, to prevent event receiver to fire several times, there is a common practice in SharePoint: just use DisableEventFiring and EnableEventFiring methods.

internal void UpdateItemOnRootwebList(SPWeb leafWeb, SPListItem leafItem, string rootWebListName, string contentTypeName, List<string> fieldsToUpdate)
{
    try
    {
        this.DisableEventFiring();

        // do your work here...

    }
    finally
    {
        this.EnableEventFiring();
    }
}

If this will not help (for example if different instances of the receiver class are involved), you could then create a static variable in your item receiver and check it from within of the method, like this:

static bool Disabled = false;

// ...

internal void UpdateItemOnRootwebList(SPWeb leafWeb, SPListItem leafItem, string rootWebListName, string contentTypeName, List<string> fieldsToUpdate)
{

    try
    {
        if (Disabled)
            return;

        Disabled = true;

        // do your work here...

    }
    finally
    {
        Disabled = false;
    }
}