ASP.NET Custom Server Controls: Cute Image Hover Button - Understanding the life cycle – Rendering methods

(Page 2 of 4 )

The default “Render” method (when not overridden by us) usually calls the “RenderBeginTag” before calling any other methods.  The “RenderBeginTag” method in my control has been implemented something like this:

Public Overrides Sub RenderBeginTag(ByVal writer As System.Web.UI.HtmlTextWriter)
        AddAttributesToRender(writer)
        writer.RenderBeginTag(HtmlTextWriterTag.Table)
        writer.RenderBeginTag(HtmlTextWriterTag.Tr)
        writer.RenderBeginTag(HtmlTextWriterTag.Td)
   End Sub

Within the above method, I am trying to call the “AddAttributesToRender(Writer)” statement to add any attributes to my button control (in this case it is simply a TABLE tag).  In fact, it is not a user defined method; it has been already defined within the “WebControl” class, and I am about to override it.  Usually, the “AddAttributesToRender” method is initiated from within the “RenderBeginTag” method (that too as the first statement).  I hope you can understand the second statement, which actually renders “<TABLE…..><TR><TD>” (with all the attributes emitted by “AddAttributesToRender” method) to the client (browser).  Make a note that -- the tags have not yet been closed!

Coming to the next code fragment, I have an empty method as follows:

Protected Overrides Sub RenderContents(ByVal writer As System.Web.UI.HtmlTextWriter)
        writer.Write(Text)
   End Sub

The above method does nothing apart from displaying the content (or text in this case) following the previous set of tags.  In this case, we don’t have any child controls.  So, I don’t need to include “base.Render(writer)” as the last statement.  Going further we have the following:

Public Overrides Sub RenderEndTag(ByVal writer As System.Web.UI.HtmlTextWriter)
        writer.RenderEndTag() 'closing td
        writer.RenderEndTag() 'closing tr
        writer.RenderEndTag() 'closing table
   End Sub

The above method simply contains three statements as “writer.RenderEndTag”.  We already opened few tags using “writer.RenderBeginTag(…)” within the RenderBeginTag” method.  We didn’t close them anywhere.  And we do that using the above method.  You need not even specify which tag to close.  It could automatically understand (from our proper HTML hierarchy) which tag to close.  That’s the beauty of ASP.NET custom control development.

Next: Understanding the life cycle – Attributes >>
 

More ASP.NET Articles
More By Jagadish Chaterjee

Comments On: ASP.NET Custom Server Controls: Cute Image Hover Button

· Hello guys...the next control is on its way...don't hesitate to ask for enhancements...   >>> Post your comment now!