This is the fourth and final part of the post describing how to create a custom lookup field for SharePoint.<\/p>\n
Other pages in this post are:<\/p>\n
This post describes how to implement the hidden related field for controlling the display within views.<\/p>\n
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To begin with, create a new class that inherits from the SPFieldMultiLineText<\/a> class.<\/p>\n This class will be used to control the display within views, which we implement by creating an XSLT to control which field to use for rendering.<\/p>\n This file (fldtypes_SPS_LookupFieldType.xsl) should be created in the ~hive\\Template\\Layouts\\XSL folder.<\/p>\n The first template in this file matches the ExtendedLookupFieldType field type, which is the master field used to store the lookup data.<\/p>\n We start here by retrieving the field definition for the field and then get the identifier for the field.<\/p>\n This is then passed into the string-replace-with template which performs some basic string replacement to remove the dashes (-) from the Guid, so we are left with a string 32 characters in length.<\/p>\n Using this, we are able to retrieve the associated hidden field which is named using the identifier for the master field, which is then used to render the content for the list item.<\/p>\n We’ll come to the creation of the hidden associated field next. For this we need to edit the RelatedLookupDataFieldType<\/em> class we created back in post 1<\/a>.<\/p>\n What we’ve done here is override the OnAdded<\/em> method of the base lookup field class and call a custom AddRelatedField<\/em> method.<\/p>\n This method creates a new field based on the one created during this part of the blog post – RelatedLookupDataFieldType<\/em>. As we don’t want users to be aware of this field it’s created as a hidden field and set to read only. We set UnlimitedLengthInDocumentLibrary<\/em> to true to ensure there we’re able to store the serialised object string containing the selected lookup field data. More on this later.<\/p>\n Next, we associate this new field with the master lookup field by adding it to the list of field references for it. This ensures that whenever the master field is added to a view, this hidden field will also be added, allowing the XSLT to find it. If we didn’t do this, the rendering would fail as there would be no way for a general user to manually add a hidden field to a view. Also, there’s no way through the object model to achieve this, hence the injection of XML into the SchemaXml property.<\/p>\n Lastly, we update the constructors to call the EnsureAssociatedField method. This helps to ensure the field reference has been correctly applied to the field definition as the field is instantiated.<\/p>\n To ensure that whenever a custom lookup field is removed from a list, the following code is implemented to ensure the hidden related field is also removed.<\/p>\n This time, we’re overriding the OnDeleting<\/em> method from the base class and calling RemoveRelatedFields<\/em> to delete the field from the list. Before calling delete it’s necessary to update the field to not be read only or hidden, otherwise the delete call will fail.<\/p>\n Remember, the data is being stored as a serialised ExtendedLookupData<\/em> object in the hidden associated field by the master field when it is saved. This is what will be passed into the GetFieldValueAsHtml<\/a> method implemented next.<\/p>\n Here, the object passed into the method is deserialised into an ExtendedLookupData<\/em> object, which as long as there are stored values, the object is processed to obtain the HTML to display in the view.<\/p>\n This method is using a custom caching class (part of the download) to retrieve previously processed lists, where the display form url is stored.<\/p>\n As long as there is a valid list, the GetItemLinks<\/em> method is subsequently called.<\/p>\n This method iterates through the stored values and checks to see if there is a valid and current lookup item for it. If there is, a link is created to allow a user viewing the result within a view to navigate to the source lookup item. Otherwise, static text is displayed.<\/p>\n The method GetCurrentFieldValue<\/em> returns the current display value for an existing item. This may differ to what was originally selected when creating the master field value but the point of this field is to either display the active value and when this does not exist, to display the user’s original selection.<\/p>\n GetCurrentFieldValue<\/em> is shown below:<\/p>\n This method also utilises caching but this time to store and retrieve the field information. If a field exists for the lookup item, its current display value is stored. If the field no longer exists, the value the user selected when creating the field is stored against the field id in the cache.<\/p>\n In the GetFieldValueAsHtml method, when the result is empty, caused by the source list no longer existing for example, the following method is called to produce a list of the stored values as static text, taken from the ExtendedLookupFieldControl<\/em> object<\/p>\n The last part of the post is to create the XML definition file for the hidden field, which as with the main field, should be created in the ~hive\\Template\\XML folder.<\/p>\n Click here<\/a> to download the code for this project.<\/p>\n","protected":false},"excerpt":{"rendered":" This is the fourth and final part of the post describing how to create a custom lookup field for SharePoint. Other pages in this post are: Part 1 – Creating a custom lookup field type Part 2 – Add field … Continue reading \r\npublic class RelatedLookupDataFieldType : SPFieldMultiLineText\r\n{\r\n public RelatedLookupDataFieldType(SPFieldCollection fields, string fieldName)\r\n : base(fields, fieldName)\r\n {\r\n }\r\n\r\n public RelatedLookupDataFieldType(SPFieldCollection fields, string typeName, string displayName)\r\n : base(fields, typeName, displayName)\r\n {\r\n }\r\n}\r\n<\/pre>\n\r\n
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\r\n\r\npublic ProcessLookupFieldType(SPFieldCollection fields, string fieldName)\r\n : base(fields, fieldName)\r\n{\r\n EnsureAssociatedField();\r\n}\r\n\r\npublic ProcessLookupFieldType(SPFieldCollection fields, string typeName, string displayName)\r\n : base(fields, typeName, displayName)\r\n{\r\n EnsureAssociatedField();\r\n}\r\n\r\nprivate void EnsureAssociatedField()\r\n{\r\n if (Id == Guid.Empty || ParentList == null || !ParentList.Fields.ContainsFieldWithStaticName(RelatedFieldName))\r\n return;\r\n \r\n XmlDocument doc = new XmlDocument();\r\n doc.LoadXml(SchemaXml);\r\n if (doc.DocumentElement == null)\r\n return;\r\n\r\n XmlNodeList nodes = doc.DocumentElement.SelectNodes(string.Format(\"\/\/FieldRefs\/FieldRef[@Name='{0}']\", RelatedFieldName));\r\n if (nodes != null && nodes.Count > 0)\r\n return;\r\n\r\n bool allowUnsafeUpdates = ParentList.ParentWeb.AllowUnsafeUpdates;\r\n try\r\n {\r\n ParentList.ParentWeb.AllowUnsafeUpdates = true;\r\n AssociateInternalName(RelatedFieldName);\r\n base.Update();\r\n }\r\n finally\r\n {\r\n ParentList.ParentWeb.AllowUnsafeUpdates = allowUnsafeUpdates;\r\n }\r\n}\r\n\r\npublic override void OnAdded(SPAddFieldOptions op)\r\n{\r\n AddRelatedField();\r\n base.OnAdded(op);\r\n Update();\r\n}\r\n\r\npublic string RelatedFieldName { get { return string.Concat(\"r_\", Id.ToString(\"N\")).Substring(0, 32); } }\r\n\r\nprivate void AddRelatedField()\r\n{\r\n SPList list = SPContext.Current.List;\r\n SPFieldCollection fields = list.Fields;\r\n\r\n SPFieldMultiLineText field = new SPFieldMultiLineText(fields, \"RelatedLookupDataFieldType\", RelatedFieldName);\r\n field.ReadOnlyField = true;\r\n field.RichText = false;\r\n field.UnlimitedLengthInDocumentLibrary = true;\r\n field.Hidden = true;\r\n\r\n string internalName = fields.Add(field);\r\n list.Update();\r\n\r\n AssociateInternalName(internalName);\r\n}\r\n\r\nprivate void AssociateInternalName(string fieldInternalName)\r\n{\r\n XmlDocument doc = new XmlDocument();\r\n\r\n doc.LoadXml(SchemaXml);\r\n XmlElement fieldRefs = doc.CreateElement(\"FieldRefs\");\r\n fieldRefs.InnerXml = string.Format(\"\r\npublic override void OnDeleting()\r\n{\r\n RemoveRelatedFields();\r\n base.OnDeleting();\r\n}\r\n\r\nprivate void RemoveRelatedFields()\r\n{\r\n if (SPContext.Current.List.Fields.ContainsField(RelatedFieldName))\r\n {\r\n SPField field = SPContext.Current.List.Fields.GetFieldByInternalName(RelatedFieldName);\r\n field.ReadOnlyField = false;\r\n field.Hidden = false;\r\n field.Update();\r\n SPContext.Current.List.Fields.Delete(field.InternalName);\r\n }\r\n}\r\n<\/pre>\n\r\npublic override string GetFieldValueAsHtml(object value)\r\n{\r\n if (value != null)\r\n {\r\n string data = SPHttpUtility.HtmlDecode(value.ToString());\r\n ExtendedLookupData lookupData = Serialization\r\nprivate string GetFieldValuesAsLinks(ExtendedLookupData itemdata)\r\n{\r\n Dictionary\r\nprivate string GetItemLinks(string displayFormUrl, ExtendedLookupData lookupData)\r\n{\r\n StringBuilder sb = new StringBuilder();\r\n\r\n int position = 0;\r\n foreach (KeyValuePair\r\nprivate string GetCurrentFieldValue(Guid webId, Guid listId, Guid valueFieldId, Guid displayFieldId, int storedValueId, string storedValue, out bool exists)\r\n{\r\n string cacheKey = string.Format(\"extendedLookupFieldValue_{0}_{1}_{2}\", webId, listId, storedValueId);\r\n string key = displayFieldId.ToString(\"B\");\r\n\r\n Dictionary\r\npublic override string GetFieldValueAsText(object value)\r\n{\r\n if (value != null)\r\n {\r\n ExtendedLookupData lookupData;\r\n if (value is ExtendedLookupData)\r\n lookupData = value as ExtendedLookupData;\r\n else\r\n lookupData = Serialization\r\n\r\n