HttpResponse.AddCacheItemDependency Method (String)

 
System_CAPS_noteNote

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Makes the validity of a cached response dependent on another item in the cache.

Namespace:   System.Web
Assembly:  System.Web (in System.Web.dll)

Public Sub AddCacheItemDependency (
	cacheKey As String
)

Parameters

cacheKey
Type: System.String

The key of the item that the cached response is dependent upon.

When the item corresponding to the cacheKey parameter is removed from the cache, the cached response of the current item is invalid.

The following example is an ASP.NET user control that is output cached. The code for the control calls the AddCacheItemDependency method with the key of an item stored in the Cache object passed as its parameter. If the item does not exist in the cache, the control's response that was stored in the output cache is invalidated. This means that on the subsequent request, a new version of the control's response will be added to the output cache.

Next, the code checks whether an item associated with a bookData key is stored in the Cache object, and displays one of two lines of text dependent upon the result. Then, the code sets the DataSource property of a DataGrid control, which is named dgBooks, with a call to a custom DataHelper class' shared GetBookData method, and populates the DataGrid with the DataBind method.

<%@ Control Language="vb" %>
<%@ Outputcache duration="10" varybyparam="none" shared="True" %>
<%@ Import Namespace="Samples.AspNet.VB" %>
<%@ Import Namespace="System.Data" %>
<script runat="server">

    Private Sub Page_Load(sender As Object, e As System.EventArgs)

        ' Make user control invalid if the 
        ' cache item changes or expires.
        Response.AddCacheItemDependency("bookData")


        ' Create a DataView object.
        Dim source As DataView = Cache("bookData")

        ' Check if the view is stored in the cache
        ' and generate the right label text
        ' dependent upon what is returned.
        If source Is Nothing Then

           source = DataHelper.GetBookData()
           lblCacheMsg.Text = "Data generated explicitly."
        Else
           lblCacheMsg.Text = "Data retrieved from application cache."
        End If

        dgBooks.DataSource = source
        dgBooks.DataBind()

        lblOutputMessage.Text = DateTime.Now.ToString()
    End Sub

</script>

    <table>
        <tbody>
            <tr>
                <th>
                    Books</th>
                <td>
                </td>
            </tr>
            <tr>
                <td>
                    <asp:DataGrid id="dgBooks" runat="server"></asp:DataGrid>
                </td>
                <td>
                </td>
            </tr>
            <tr>
                <td>
                    <asp:Label id="lblCacheMsg" runat="server"></asp:Label>
                </td>
                <td>
                </td>
            </tr>
            <tr>
                <td>
                    The control was created at: 
                </td>
                <td>
                    <asp:Label id="lblOutputMessage" runat="server"></asp:Label>
                </td>
            </tr>
        </tbody>
    </table>

.NET Framework
Available since 1.1
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