Yesterday I solved one caching problem with local community portal. I enabled output cache on SharePoint Server 2007
to make site faster. Although caching works fine I needed
to do some additional work because there are some controls that show different content
to different users. In this example I will show you how
to use “donut caching” with user controls – powerful way
to drive some content around cache. About donut caching Donut caching means that although you are caching your content you have some holes in it so you can still affect the output that goes
to user. By example you can cache front page on your site and still show welcome message that contains correct user name.
To get better idea about donut caching I suggest you
to read ScottGu posting Tip/Trick: Implement "Donut Caching" with the ASP.NET 2.0 Output Cache Substitution Feature. Basically donut caching uses ASP.NET substitution control. In output this control is replaced by string you return from static method bound
to substitution control. Again, take a look at ScottGu blog posting I referred above. Problem If you look at Scott’s example it is pretty plain and easy by its output. All it does is it writes out current user name as string. Here are examples of my login area for anonymous and authenticated users: It is clear that outputting mark-up for these views as string is pretty lame
to implement in code at string level. Every little change in design will end up with new version of controls library because some parts of design “live” there. Solution: using user controls I worked out easy solution
to my problem. I used cache substitution and user controls together. I have three user controls: LogInControl – this is the proxy control that checks which “real” control
to load. AnonymousLogInControl – template and logic for anonymous users login area. AuthenticatedLogInControl – template and logic for authenticated users login area. This is the control we render for each user separately because it contains user name and user profile fill percent. Anonymous control is not very interesting because it is only about keeping mark-up in separate file. Interesting parts are LogInControl and AuthenticatedLogInControl. Creating proxy control The first thing was
to create control that has substitution area where “real” control is loaded. This proxy control should also be available
to decide which control
to load. The definition of control is very primitive. <%@ Control EnableViewState="false" Inherits="MyPortal.Profiles.LogInControl" %> <asp:Substitution runat="server" MethodName="ShowLogInBox" /> But code is a little bit tricky. Based on current user instance we decide which login control
to load. Then we create page instance and
load our control through it. When control is loaded we will call DataBind() method. In this method we evaluate all fields in loaded control (it was best choice as
Load and other events will not be fired). Take a look at the code. public static string ShowLogInBox(HttpContext context) { var user = SPContext.Current.Web.CurrentUser; string controlName; if (user != null) controlName = "AuthenticatedLogInControl.ascx"; else controlName = "AnonymousLogInControl.ascx"; var path = "~/_controltemplates/" + controlName; var output = new StringBuilder(10000); using(var page = new Page()) using(var ctl = page.LoadControl(path)) using(var writer = new StringWriter(output)) using(var htmlWriter = new HtmlTextWriter(writer)) { ctl.DataBind(); ctl.RenderControl(htmlWriter); } return output.ToString(); } When control is bound
to data we ask
to render it its contents
to StringBuilder. Now we have the output of control as string and we can return it from our method. Of course, notice how correct I am with resources disposing. :) The method that returns contents for substitution control is static method that has no connection with control instance because hen page is read from cache there are no instances of controls available. Conclusion As you saw it was not very hard
to use donut caching with user controls. Instead of writing mark-up of controls
to static method that is bound
to substitution control we can still use our user controls.
