Vedant Kulshreshtha

I have no special talents. I am only passionately curious.

Using Custom ASP.NET Controls in SharePoint 2007

Using Custom ASP.NET Controls in SharePoint 2007

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Like ASP.NET Web Parts you can also use ASP.NET Controls in SharePoint 2007. I have put together a comparison between them in context of their use in SharePoint:

Similarities

  • Custom Properties are supported
  • Can exist inside as well as outside a web part zone
  • Can be used in a master page or page layout
  • Needs a SafeControl entry in web.config file
  • Runs under SharePoint and current user context

Advantage of Web Parts

  • Web Part Gallery is available to manage them at site collection level
  • Can be added/removed using web browser or SharePoint Designer or even a C# code
  • When inside a Web Part Zone, Web Parts can be moved around and also personalized by end-users using a web browser
  • Default/Custom Editor Part can be used to manage properties through web browser
  • Audience targeting can be used
  • Can be used in a content/site page

Advantage of Controls

  • Cannot be added/removed using web browser or C# code. It can be added/removed only using SharePoint Designer
  • Useful for scenarios where a control needs to be in every page of site/web or if output is not visible in UI
  • Can be used to put content in web page header dynamically. For example: a custom meta tag or a stylesheet based on current user, web, file or some other business rule


SharePoint also uses custom WebControls a lot. Some examples ("<" and "/>" tags have been removed from beginning and end of each line):

  • SharePoint:CssLink runat="server"
  • SharePoint:ScriptLink language="javascript" name="core.js" Defer="true" runat="server"
  • SharePoint:SPCalendarNavigator id="CalendarNavigatorId" runat="server"
  • PublishingWebControls:RichImageField id="ImageField" FieldName="PublishingPageImage" runat="server"


To create a custom Control:

  • Create a Class Library project
  • Inherit from WebControl class in System.Web.UI.WebControls namespace or Control class in System.Web.UI namespace
  • Override the "Render" or "RenderContents" method

To use the custom Web Control:

  • Put the custom control assembly in Bin directory of Web application (GAC may also be used)
  • Mark it as a safe control in web.config
  • Open master page or a page layout file
  • Register the control using Register directive and assign a TagPrefix
  • Use the control using the TagPrefix and Class name

Some tips from the MSDN article "Walkthrough: Developing and Using a Custom Server Control" :

  • If your control renders a user interface (UI) element or any other visible element on the client, you should derive your control from System.Web.UI.WebControls.WebControl (or a derived class)
  • If your control renders an element that is not visible in the client browser, such as a hidden element or a meta element, derive your control from System.Web.UI.Control
  • If your control extends the functionality of an existing control, such as the Button, Label, or Image controls, you can derive from that control
  • In general, when your control derives from WebControl and renders a single element, you should override the RenderContents method (and not the Render method) to render content within the control's tags
  • ToolboxDataAttribute specifies the format string for the element. The string becomes the control's markup when the control is double-clicked in the toolbox or dragged from the toolbox onto the design surface

Sample code: following code adds current web's Title as content of Keywords Meta Tag

public class CustomMetaTag : WebControl {

protected override HtmlTextWriterTag TagKey {

get { return HtmlTextWriterTag.Meta; }

}

protected override void AddAttributesToRender(HtmlTextWriter writer) {

base.AddAttributesToRender(writer);

writer.AddAttribute(HtmlTextWriterAttribute.Name, "keywords");

SPWeb web = SPControl.GetContextWeb(Context);

writer.AddAttribute(HtmlTextWriterAttribute.Content, web.Title);

}

}

Note: a very good example of using a custom WebControl is given in this blog entry by Waldek Mastykarz -> Extending the SharePoint:FieldValue WebControl

 

Comments
  • PingBack from http://sovit.biz/vedants-blog-using-custom-aspnet-controls-in-sharepoint-2007/

  • Hi Vedant, I have a question: When I try to add a server control to the SPD design surface I get the following error: "Error rendering control Control1 - An error occurred while fetching preview"

    I am using SPD in MOSS and am logged in as domain admin.

    I have made the change in Local Security policy to allow Authenticated Users to Bypass Traverse Checking (as per Mike Walshs commenst)

    Any suggestion would be greatly appreciated as this is has halted a live development project.

    Regards

    Gary

  • Hi Vedant,

    Any idea, how different it is in SP 2010?

    I have created a control, deployed and kept it on a master page. In SPD I see the control, but not in the browser. Can you give an insight on this?

  • Thanks bro.

    You don't know what you have done to me!:D

    >:D<

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