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SPFieldLink class

Represents a single column (also known as field) reference that is included in a content type.

System.Object
  Microsoft.SharePoint.SPFieldLink

Namespace:  Microsoft.SharePoint
Assembly:  Microsoft.SharePoint (in Microsoft.SharePoint.dll)

'Declaration
PublicClassSPFieldLink
'Usage
DiminstanceAsSPFieldLink

If you want to track certain item metadata in a content type, you can reference a column that represents that metadata. However, you cannot create a column in a content type; you must create the column separately and then reference it in the content type definition. As a result, when you add a column to a content type, the content type contains a reference to the column (or field), rather than the column (or field) itself.

The reference contains a subset of the properties of the full field definition. These are the properties you can customize for the column as it exists in the content type.

For more information, see Fields and Field References.

The SPContentType object contains both a SPFieldLinkCollection and an SPFieldCollection object.

The SPFieldCollection object provides you with a combined view of a column's attributes, as they exist in the specified content type. Each SPField object represents all the attributes of a column or field definition, combined with those attributes that have been overridden in the field reference for that content type.

When you access an SPField object in a content type, SharePoint Foundation combines the field definition with the field reference and returns the resulting SPField object. This is helpful because you do not have to look up a field definition and all the attributes in the field definition that are overridden by the field reference for that content type.

There is a 1-to-1 correlation between the items in the SPFieldLinkCollection and SPFieldCollection objects. For each SPFieldLink object that you add to a content type, SharePoint Foundation adds a corresponding SPField object that represents the combined view of that column as defined in the content type.

NoteNote

SharePoint Foundation does not support inheriting from the SPFieldLink class.

The following example shows a console application that creates a content type, applies it to a list, and adds references to fields at both the site and list level.

Imports System
Imports Microsoft.SharePoint

Module ConsoleApp
    Sub Main()
        Dim site As SPSite = New SPSite("http://localhost")
        Try
            Dim web As SPWeb = site.OpenWeb()
            Try
                Dim contentTypeName As String = "Spec"
                Dim listTitle As String = "Product Specs"
                Dim docType As SPContentType = web.AvailableContentTypes("Document")

                ' Create a content type.
                Dim siteContentType As New SPContentType(docType, _
                                                         web.ContentTypes, contentTypeName)
                ' Add the content type to the site collection.
                siteContentType = web.ContentTypes.Add(siteContentType)

                ' Change the name of the Title field in the content type.
                siteContentType.FieldLinks("Title").DisplayName = "Product"

                ' Add a field to the site field collection.
                Dim siteField As SPField = AddField("Owner", SPFieldType.Text, web.Fields)

                ' Reference the field in the content type.
                AddFieldLink(siteField, siteContentType)
                siteContentType.Update()

                ' Create and configure a document library. 
                Dim listId As Guid = web.Lists.Add(listTitle, _
                                                   "A library of product specifications", _
                                                    SPListTemplateType.DocumentLibrary)
                Dim library As SPDocumentLibrary = CType(web.Lists(listId), SPDocumentLibrary)
                library.OnQuickLaunch = True
                library.ContentTypesEnabled = True
                library.EnableFolderCreation = False 'Hide "Folder" on the New menu
                library.Update()

                ' Add the site content type to the library.
                Dim listContentType As SPContentType = library.ContentTypes.Add(siteContentType)

                ' Add a field to the list field collection.
                Dim listField As SPField = AddField("SKU", SPFieldType.Text, library.Fields)

                ' Reference the field in the list version of the new content type.
                AddFieldLink(listField, listContentType)
                listContentType.Update()

                ' Remove the document content type. 
                Dim id As SPContentTypeId = library.ContentTypes(docType.Name).Id
                library.ContentTypes.Delete(id)
                library.Update()

                ' Review our work.
                Console.WriteLine("Site content type")
                PrintFieldNames(siteContentType)
                Console.WriteLine("List content type")
                PrintFieldNames(listContentType)
            Finally
                web.Dispose()
            End Try
        Finally
            site.Dispose()
        End Try
        Console.Write("Press ENTER to continue...")
        Console.ReadLine()
    End Sub

    Function AddField(ByVal title As String, ByVal type As SPFieldType, _
                      ByRef fields As SPFieldCollection) As SPField
        ' If the field is not in the collection,
        If Not (fields.ContainsField(title)) Then
            ' Add it.
            fields.Add(title, type, False)
        End If
        Return fields.GetField(title)
    End Function

    Sub AddFieldLink(ByRef field As SPField, ByRef contentType As SPContentType)
        ' Is the FieldLink in the collection?
        Dim fieldLink As SPFieldLink = contentType.FieldLinks(field.Id)
        If fieldLink Is Nothing Then ' No, so add it.
            fieldLink = New SPFieldLink(field)
            contentType.FieldLinks.Add(fieldLink)
        End If
    End Sub

    Sub PrintFieldNames(ByVal contentType As SPContentType)
        For Each link As SPFieldLink In contentType.FieldLinks
            Dim field As SPField = contentType.Fields(link.Id)
            ' Screen out system fields.
            If field.Reorderable AndAlso field.InternalName <> "FileLeafRef" Then
                Console.WriteLine("FieldLink.DisplayName = {0}", link.DisplayName)
            End If
        Next link
        Console.WriteLine()
    End Sub
End Module

The application prints the following output to the console.

Site content type
FieldLink.DisplayName = Product
FieldLink.DisplayName = Owner

List content type
FieldLink.DisplayName = Product
FieldLink.DisplayName = Owner
FieldLink.DisplayName = SKU

Press ENTER to continue...

Any public static (Shared in Visual Basic) members of this type are thread safe. Any instance members are not guaranteed to be thread safe.
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