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When Is Read Only Not Read Only?

Whilst developing some code in ID-Sharepoint to programatically create content types I came across one of those things that, as a Sharepoint developer, make you MAD!
 
I was accessing a content type using code like this :
 
SPContentType contentTypeWotIWantToChange = web.AvailableContentTypes("ContentTypeWotIWantToChange");
 
I then coded up the addition of a couple of site columns to the content type like this:
 
contentTypeWotIWantToChange.FieldLinks.Add(new SPFieldLink(……
contentTypeWotIWantToChange.FieldLinks.Add(new SPFieldLink(……
….
 
I then used this code to update the content type:
 
contentTypeWotIWantToChange.Update(true)
 
and was greeted, upon running this code, with an exception "the collection cannot be modified".
 
Much head scratching resulted and I checked contentTypeWotIWantToChange to see if it was set as "ReadOnly" or "Sealed" – both false so that wasn’t it…
 
Much more head scratching and re-reading of msdn and other info revealed that .AvailableContentTypes is a read only collection of content types that represent content types from the current web and parent webs so I guess it makes some kind of sense to disallow the update of content types that may have been provisioned at a level above where you are but I do think there should be a bit more of a clue – I guess the content types can’t be marked as read only or as sealed but I do think the property could be a bit clearer in  it’s intent i.e. maybe called it ActiveContentTypesReadOnly? 
 
Anyway, the solution was to use this code to get the contentytpye
 
SPContentType contentTypeWotIWantToChange = web.ContentTypes("ContentTypeWotIWantToChange");
 
Which gets the content types from the current web only and is read/write.
 
The rest of the code was unchanged.
 
Chalk up another lost hour to SharePoint dev…..
 
Read about AvailableContentTypes here and ContentTypes here
 
Happy SharePoint deving ……..
 
 
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One Response to “When Is Read Only Not Read Only?”

  1. I feel your pain. I\’ve had similar issues with two properties working on the same data, only behaving differently. I was trying to control the Content Types on the start menu:http://www.novolocus.com/2009/05/26/control-the-content-types-in-the-new-menu-via-code/ Another gem I\’ve hit a few times is where an accessor returns a different copy of an object each time. For example, SPList.DefaultView returns a different SPView each time you call it. Nice :/http://www.novolocus.com/2009/02/09/wss-practice-create-a-list-columns-and-view-programmatically/


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