Partial Page Output Caching Using VaryByControl

The

VaryByControl directive provides a helpful shortcut to vary the User Controls output

by a contained control.

<%@ Imports Namespace="System.Data.SqlClient" %>

<%@ OutputCache Duration="60" VaryByControl="SortBy" %>

<script runat="server">

Sub Page_Load (sender As object, e As EventArgs)

Dim connection As New SqlConnection([your connection string])

Dim command As New SqlCommand("BookSelection", connection)

' Mark as a stored procedure

command.CommandType = CommandType.StoredProcedure

' Set up a SQL parameter for the book type selected

command.Parameters.Add("@BookType",

➥SqlDbType.NVarChar, 25).Value =

➥SortBy.SelectedItem.Value

' Execute

connection.Open()

BookListing.DataSource = command.ExecuteReader()

BookListing.DataBind()

connection.Close()

End Sub

</script>

<form runat="server">

Please select the types of books you are interested in:

<asp:DropDownList AutoPostBack="true" id="SortBy" runat="server" >

<asp:listitem >Technology</asp:listitem>

<asp:listitem >Fiction</asp:listitem>

<asp:listitem >Non-Fiction</asp:listitem>

</asp:DropDownList>

<br>

<asp:DataGrid runat="server" id="BookListing" />

</form>

Comments

Consider a User Control that displays a list of the top 10 books with a SortBy

DropDownList containing Technology, Fiction, and Non-Fiction.Whenever a user

changes a value in the DropDownList the server returns data filtered by the value of

SortBy.

The content generated by the User Control can be varied just as you can vary page

output cached responses. However, within a User Control, the name of the control,

SortBy, is namespaced to the name of the containing control-UserControl1:SortyBy.

This allows multiple Top10 User Controls to be hosted in the same page without experiencing

naming collisions.

For example, if you had two of these User Controls on your page, they might have

the IDs Top10Books1 and Top10Books2. Top10Books1:SortBy and Top10Books2:

SortBy are treated as separate drop-down controls.The VaryByControl option simply

allows you to avoid typing VaryByParam="Top10Books2:SortBy"-instead simply type

VaryByControl="SortBy".