This is part three of the post on how to create a custom lookup field for SharePoint.<\/p>\n
Other pages in this post are:<\/p>\n
For this post, I’ll describe the implementation of the field control class.<\/p>\n
<\/p>\n
As previously mentioned, a Visual Studio project will be available for download once this series is finished.<\/p>\n
For this class, we’ll inherit from the BaseFieldControl<\/a> class.<\/p>\n In the constructor for this class we’re taking the settings defined in the field’s definition and storing them for use later on.<\/p>\n The first thing I’ll describe is how the UI is implemented. This covers the creating\\editing and displaying of field data.<\/p>\n During the control creation stage, the control mode is queried and the class either creates controls for displaying or for editing\\creation. Similar logic is applied during the load phase of the class.<\/p>\n One thing worth noting here is the deserialization of an ExtendedLookupData object. This object is stored in the related field (see the fourth post<\/a> for the implementation of this) and is used to ensure the selected lookup values are displayed in the event the source list\\items being deleted.<\/p>\n Let’s have a look at the display mode implementation:<\/p>\n The CreateControlsForDisplay<\/em> method is pretty self explanatory.<\/p>\n InitialiseForDisplay<\/em> starts by retrieving the list object containing the lookup items by calling GetLookupList()<\/em>.<\/p>\n The next stage calls GetSelectedLookupColumns<\/em> to retrieve (see next code block) the current display values and updating any items that no longer exist (because they’ve been deleted) with the original value that was set during the item creation. Again, for further details on the ExtendedLookupColumnValues<\/em> and the hidden related field, have a look at the fourth post<\/a> for this series (coming soon).<\/p>\n Next, the InitialiseForDisplay<\/em> method calls GetFieldValuesAsLinks()<\/em> to get the display values in the form of hyperlinks to the corresponding lookup items. Where all of the lookup items no longer exist and it’s not possible to create hyperlinks the display names from the hidden related field are used to display static titles of the lookup items.<\/p>\n Lastly, for the display implementation, we render the literal control by overriding the RenderFieldForDisplay<\/a> method.<\/p>\n Create\\Edit Implmentation<\/strong><\/p>\n Now onto the creation\\editing implementation.<\/p>\n During the control creation, a simple drop down list is created when the field definition specifies that only single selection is permitted. When multiple items are allowed, CreateMultipleItemSelectionControls<\/em> is called which creates the controls required to allow the user to select more than one lookup item.<\/p>\n The control I chose to use to allow users to select multiple items was the GroupedItemPicker<\/a> control, which is part of the Microsoft.SharePoint<\/em> assembly.<\/p>\n The rest of this method simply creates a table to contain the group picker and the associated controls it requires, such as the add\\remove buttons and the candidate and selection list boxes.<\/p>\n Now onto the loading phase:<\/p>\n As with the CreateControlsForNewEdit<\/em> method, the above method checks if the field allows multiple item selection and processes the initialisation accordingly.<\/p>\n For single selection (using the drop down list) similar logic to initialising the display mode is implemented. The difference here is that lookup items that no longer exist are removed from the available options. Subsequently, saving changes when this is the case will remove the deleted item from the stored values and it will no longer appear in display mode.<\/p>\n For multiple item selection the following is implemented:<\/p>\n This method has to fill two list boxes (part of the GroupItemPicker control) one for the available lookup items and the other for the currently selected items.<\/p>\n If the mode is set to edit, the latter drop down list is bound to the item’s selected lookup items, minus those where their source has been deleted.<\/p>\n The candidate drop down list is then bound to the complete list of available lookup items. Where the mode is edit any selected items are removed from the candidate list by calling UpdateCandidateColumns<\/em>:<\/p>\n An important part of the above method is the setting of the _itemDetails variable. Here, the lookup item’s id and display values are being stored into a Dictionary object. The reason for doing this is that the GroupItemPicker control only exposes a property that allows you to read the selected item’s ids. The property that returns the display values is set to internal, so this is a workaround to allow the field control to save the selected id and display values.<\/p>\n That’s about it for the creation an initialisation of the display\\edit controls.<\/p>\n Saving<\/strong><\/p>\n The last part of this post is to describe the saving process for the field.<\/p>\n Before a save is allowed to progress, the Validate<\/a> method if overridden to ensure a value has been selected when the field settings dictate that it is a required field.<\/p>\n Now onto the save methods. First, the UpdateFieldValueInItem<\/a> method is overridden:<\/p>\n This method is called whenever a save is initiated against the field. Here additional validation is performed before serializing the ExtendedLookupData object to the hidden related field – see the fourth post<\/a> for details on how this is implemented.<\/p>\n The call to the base method ensures the Value property is hit. This property is used to get the value for the field.<\/p>\n During the setter, a new ExtendedLookupData class is initialised and configured with the identifiers for the lookup list.<\/p>\n Where multiple items are permitted the GetMultipleItemSelectionValues<\/em> method is called and the returned collection saved against the ExtendedLookupData object.<\/p>\n For single selection, the GetSingleItemSelectionValue<\/em> method is called and, once again, the returned collection saved against the ExtendedLookupData object.<\/p>\n Here, the list of selected id values from the GroupItemPicker is queried against the _itemDetails variable (created during the InitialiseMultipleItemSelectionControls<\/em> method) and where the id from the GroupItemPicker matches a key from _itemDetails a new LINQ object is created containing the id and the display value. Remember, the GroupItemPicker control does not expose the display property, only id and I don’t like to use reflection in case the underlying object changes.<\/p>\n The GetSingleItemSelectionValue<\/em> method is a bit simpler:<\/p>\n This method returns the selected id and display values from the single selection drop down list.<\/p>\n Part four of this post will continue with the creation of the custom hidden related field, Click here<\/a> to view it.<\/p>\n","protected":false},"excerpt":{"rendered":" This is part three of the post on 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 editor class Part … Continue reading \r\npublic class ExtendedLookupFieldControl : BaseFieldControl\r\n{\r\n public ExtendedLookupFieldControl(ExtendedLookupFieldType extendedLookupFieldType)\r\n {\r\n if (extendedLookupFieldType == null)\r\n throw new ArgumentNullException(\"extendedLookupFieldType\");\r\n\r\n _isInitialised = false;\r\n _webSourceId = extendedLookupFieldType.LookupWebId;\r\n _lookupListId = new Guid(extendedLookupFieldType.LookupList);\r\n _displayColumnId = new Guid(extendedLookupFieldType.LookupField);\r\n _valueColumnId = extendedLookupFieldType.ValueColumnId;\r\n _allowMultipleItemSelection = extendedLookupFieldType.AllowMultipleValues;\r\n _relatedFieldName = extendedLookupFieldType.RelatedFieldName;\r\n _isRequired = extendedLookupFieldType.Required;\r\n }\r\n}\r\n<\/pre>\n\r\nprotected override void CreateChildControls()\r\n{\r\n if (Field == null) return;\r\n\r\n base.CreateChildControls();\r\n \r\n switch (ControlMode)\r\n {\r\n case SPControlMode.Display:\r\n CreateControlsForDisplay();\r\n break;\r\n case SPControlMode.Edit:\r\n case SPControlMode.New:\r\n CreateControlsForNewEdit();\r\n break;\r\n }\r\n}\r\n\r\nprotected override void OnLoad(EventArgs e)\r\n{\r\n base.OnLoad(e);\r\n\r\n InitialiseControls();\r\n}\r\n\r\nprivate void InitialiseControls()\r\n{\r\n if (_isInitialised)\r\n return;\r\n\r\n string data = Item[_relatedFieldName] == null ? string.Empty : Item[_relatedFieldName].ToString();\r\n\r\n _lookupData = !string.IsNullOrEmpty(data) ? Serialization\r\nprivate void CreateControlsForDisplay()\r\n{\r\n ltlDisplayItems = new Literal { ID = \"ltlDisplayItems\" };\r\n Controls.Add(ltlDisplayItems);\r\n}\r\n\r\nprivate void InitialiseForDisplay()\r\n{\r\n ltlDisplayItems.Text = string.Empty;\r\n\r\n SPList lookupList = GetLookupList();\r\n List\r\nprivate List
\r\nprotected override void RenderFieldForDisplay(HtmlTextWriter output)\r\n{\r\n ltlDisplayItems.RenderControl(output);\r\n}\r\n<\/pre>\n\r\nprivate void CreateControlsForNewEdit()\r\n{\r\n if (_allowMultipleItemSelection)\r\n {\r\n CreateMultipleItemSelectionControls();\r\n }\r\n else\r\n {\r\n ddlLookupItems = new DropDownList {ID = \"ddlLookupItems\"};\r\n if (!Field.Required)\r\n {\r\n ddlLookupItems.DataBound += DropDownList_OnDataBound;\r\n }\r\n Controls.Add(ddlLookupItems);\r\n }\r\n}\r\n<\/pre>\n\r\nprivate void CreateMultipleItemSelectionControls()\r\n{\r\n const string SEPARATOR_CELL_STYLE = \"padding-left: 10px;\";\r\n const string CSS_MSLONG = \"ms-long\";\r\n const string CSS_MSINPUT = \"ms-input\";\r\n const string CSS_MSBUTTONHEIGHTWIDTH = \"ms-ButtonHeightWidth\";\r\n\r\n gipLookupItems = new GroupedItemPicker\r\n {\r\n ID = \"gipLookupItems\",\r\n CandidateControlId = \"SelectCandidate\",\r\n ResultControlId = \"SelectResult\",\r\n AddButtonId = \"btnAdd\",\r\n RemoveButtonId = \"btnRemove\"\r\n };\r\n Controls.Add(gipLookupItems);\r\n\r\n Table tblMultipleValue = new Table { ID = \"tblMultipleValue\", CellPadding = 0, CellSpacing = 0, CssClass = CSS_MSLONG };\r\n\r\n TableRow row = new TableRow();\r\n TableCell cell = new TableCell { CssClass = CSS_MSINPUT };\r\n SPHtmlSelect selectCandidate = new SPHtmlSelect {ID = \"SelectCandidate\", Width = 143, Height = 125, Multiple = true };\r\n cell.Controls.Add(selectCandidate);\r\n row.Cells.Add(cell);\r\n tblMultipleValue.Rows.Add(row);\r\n\r\n cell = new TableCell();\r\n cell.Attributes.Add(\"style\", SEPARATOR_CELL_STYLE);\r\n row.Cells.Add(cell);\r\n tblMultipleValue.Rows.Add(row);\r\n\r\n cell = new TableCell { CssClass = CSS_MSINPUT, HorizontalAlign = HorizontalAlign.Center, VerticalAlign = VerticalAlign.Middle };\r\n HtmlButton btnAdd = new HtmlButton { ID = \"btnAdd\", InnerText = \"Add\" };\r\n btnAdd.Attributes.Add(\"class\", CSS_MSBUTTONHEIGHTWIDTH);\r\n cell.Controls.Add(btnAdd);\r\n Literal litBreak = new Literal();\r\n litBreak.Text = \"
\";\r\n cell.Controls.Add(litBreak);\r\n HtmlButton btnRemove = new HtmlButton { ID = \"btnRemove\", InnerText = \"Remove\" };\r\n btnRemove.Attributes.Add(\"class\", CSS_MSBUTTONHEIGHTWIDTH);\r\n cell.Controls.Add(btnRemove);\r\n row.Cells.Add(cell);\r\n tblMultipleValue.Rows.Add(row);\r\n\r\n cell = new TableCell();\r\n cell.Attributes.Add(\"style\", SEPARATOR_CELL_STYLE);\r\n row.Cells.Add(cell);\r\n tblMultipleValue.Rows.Add(row);\r\n\r\n cell = new TableCell { CssClass = CSS_MSINPUT };\r\n SPHtmlSelect selectResult = new SPHtmlSelect { ID = \"SelectResult\", Width = 143, Height = 125, Multiple = true };\r\n cell.Controls.Add(selectResult);\r\n row.Cells.Add(cell);\r\n tblMultipleValue.Rows.Add(row);\r\n\r\n Controls.Add(tblMultipleValue);\r\n}\r\n<\/pre>\n\r\nprivate void InitialiseForNewEdit()\r\n{\r\n if (_allowMultipleItemSelection)\r\n {\r\n InitialiseMultipleItemSelectionControls();\r\n }\r\n else\r\n {\r\n if (!Page.IsPostBack)\r\n {\r\n SPList lookupList = GetLookupList();\r\n if (lookupList != null)\r\n {\r\n List\r\nprivate void InitialiseMultipleItemSelectionControls()\r\n{\r\n if (Page.IsPostBack)\r\n return;\r\n\r\n SPList lookupList = GetLookupList();\r\n if (lookupList != null)\r\n {\r\n List\r\nprivate void UpdateCandidateColumns(List
\r\npublic override void Validate()\r\n{\r\n if (_isRequired)\r\n {\r\n ErrorMessage = \"You must specify a value for this required field.\";\r\n\r\n if (_allowMultipleItemSelection)\r\n {\r\n IsValid = gipLookupItems != null && gipLookupItems.SelectedIds.Count > 0;\r\n }\r\n else\r\n {\r\n IsValid = ddlLookupItems != null && !string.IsNullOrEmpty(ddlLookupItems.SelectedItem.Value);\r\n }\r\n }\r\n else\r\n {\r\n IsValid = true;\r\n }\r\n}\r\n<\/pre>\n\r\npublic override void UpdateFieldValueInItem()\r\n{\r\n base.UpdateFieldValueInItem();\r\n \r\n if (Field.Required)\r\n {\r\n IsValid = Value != null;\r\n }\r\n\r\n if (_lookupData != null)\r\n {\r\n string data = Serialization\r\npublic override object Value\r\n{\r\n get\r\n {\r\n EnsureChildControls();\r\n InitialiseControls();\r\n\r\n _lookupData = new ExtendedLookupData();\r\n _lookupData.WebId = _webSourceId;\r\n _lookupData.ListId = _lookupListId;\r\n _lookupData.DisplayId = _displayColumnId;\r\n _lookupData.ValueId = _valueColumnId;\r\n\r\n if (_allowMultipleItemSelection)\r\n {\r\n SPFieldLookupValueCollection lookupValues = GetMultipleItemSelectionValues();\r\n AddLookupValuesToLookupData(lookupValues);\r\n return lookupValues;\r\n }\r\n \r\n SPFieldLookupValue lookupValue = GetSingleItemSelectionValue();\r\n if (lookupValue != null)\r\n {\r\n AddLookupValueToLookupData(lookupValue);\r\n }\r\n return lookupValue;\r\n }\r\n set\r\n {\r\n }\r\n}\r\n<\/pre>\n\r\nprivate SPFieldLookupValueCollection GetMultipleItemSelectionValues()\r\n{\r\n SPFieldLookupValueCollection lookupValues = new SPFieldLookupValueCollection();\r\n\r\n if (gipLookupItems.SelectedIds == null || gipLookupItems.SelectedIds.Count > 0)\r\n {\r\n \/\/ From all available items, filter by the selected item ids.\r\n lookupValues.AddRange(from KeyValuePair\r\nprivate SPFieldLookupValue GetSingleItemSelectionValue()\r\n{\r\n SPFieldLookupValue lookupValue = null;\r\n\r\n if (ddlLookupItems != null && !string.IsNullOrEmpty(ddlLookupItems.SelectedItem.Value))\r\n {\r\n lookupValue = new SPFieldLookupValue(Convert.ToInt32(ddlLookupItems.SelectedItem.Value), ddlLookupItems.SelectedItem.Text);\r\n }\r\n\r\n return lookupValue;\r\n}\r\n<\/pre>\n