DOT NET Interview Questions - DotNetSpider

(P)Can you show a simple code showing file dependency in cache ?
Partial Class Default_aspx
Public Sub displayAnnouncement()
Dim announcement As String
If Cache(“announcement”) Is Nothing Then
Dim file As New _
System.IO.StreamReader _
(Server.MapPath(“announcement.txt”))
announcement = file.ReadToEnd
file.Close()
Dim depends As New _
System.Web.Caching.CacheDependency _
(Server.MapPath(“announcement.txt”))
Cache.Insert(“announcement”, announcement, depends)
End If
Response.Write(CType(Cache(“announcement”), String))
End Sub
Private Sub Page_Init(ByVal sender As Object, ByVal e As
System.EventArgs) Handles Me.Init
displayAnnouncement()
End Sub
End Class
Note :- Above source code can be obtained from CD in “CacheSample”
folder.”Announcement.txt” is in the same folder which you can play around to see the
results.
Above given method displayAnnouncement() displays banner text from Announcement.txt
file which is lying in application path of the web directory.Above method first checks is
the Cache object nothing , if the cache object is nothing then it moves further to load the
cache data from the file.Whenever the file data changes the cache object is removed and
set to nothing.
(A) What is Cache Callback in Cache ?
Cache object is dependent on its dependencies example file based , time based etc.Cache
items remove the object when cache dependencies change.ASP.NET provides capability
to execute a callback method when that item is removed from cache.
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