Add site column to site content type error

Question

var objWeb = properties.Feature.Parent as SPWeb;
Guid webPublishingGuid = new Guid("94c94ca6-b32f-4da9-a9e3-1f3d343d7ecb");
SPFeature feature = null;
SPSite site = objWeb.Site;
feature = objWeb.Features[webPublishingGuid];
if (feature == null) 
{
    SPContentType contentType = objWeb.ContentTypes["Wiki Page"];
    SPField field = objWeb.Fields["Keywords"];
    SPFieldLink fieldLink = new SPFieldLink(field);
    contentType.FieldLinks.Add(fieldLink);
    contentType.Update(true);
}

I want to add site column keyword to site content type wiki page. Above is my code I wrote in my FeatureActivated method.

This works when I execute this code in the default site. My problem is it throws an exception that your keyword column is null when I execute that code in sub site or other team sites.

Answer 1

Your site column may not exist in the sub-site.

You probably are creating the Keywords site column in the root web of the site collection (Or is keywords a default one? If so, it'll be in the root web too).

You can check this from the Site Column Gallery in the Site Settings. Check to see what site it's created in.

If so, you'll need to use:

SPField field = site.RootWeb.Fields["Keywords"];

That's my guess.

Answer 2

In your feature, since it can be activated at multiple scopes, you should check if the field exists, if it doesn't create it, then add it to your content type. This removes the manual process of creating the site column.

SPWeb web = properties.Feature.Parent as SPWeb;
SPField field = web.Fields.TryGetFieldByStaticName("Keywords");
if (field != null)
{
    SPContentType contentType = web.ContentTypes["Wiki Page"];
    SPFieldLink fieldLink = new SPFieldLink(field);
    contentType.FieldLinks.Add(fieldLink);
    contentType.Update(true);
}

The method web.Fields.TryGetFieldByStaticName(); will not throw an exception. It returns null if no fields exist.

As a side question, what are you trying to do? Are you checking for a dependent feature?