Postback Issue Cache Busting my CSS files in my App_Themes folder

Question

I have two stylesheets in my App_Themes/Default/ folder: BaseStylesheet.css and NonConvert.css

Here is the code that I have on my example webform. I add the LastModifiedDate to the end of each of my CSS files in my App_Themes folder. When they are updated, the LastModifiedDate automatically updates.

Protected Sub Page_PreRender(sender As Object, e As EventArgs) Handles Me.PreRender
    'CACHING - Add a LastModifiedDate to all CSS files in the App_Themes directory
    Dim link As HtmlLink = Nothing
    For Each c As Control In Header.Controls
        If TypeOf c Is HtmlLink Then
            link = TryCast(c, HtmlLink)
            If link.Href.IndexOf("App_Themes/", StringComparison.InvariantCultureIgnoreCase) >= 0 AndAlso link.Href.EndsWith(".css", StringComparison.InvariantCultureIgnoreCase) Then
                link.Href += String.Format("?t={0}", GetLastModifiedDateString(link.Href))
            End If
        End If
    Next
End Sub

Public Shared Function GetLastModifiedDateString(ByVal filePath As String) As String
    Dim fileInfo As New IO.FileInfo(System.Web.HttpContext.Current.Server.MapPath(filePath))
    If fileInfo.Exists Then
        Return String.Format("{0:yyyyMMddHHmmss}", fileInfo.LastWriteTimeUtc)
    End If
    Return String.Empty
End Function

These two methods are working just fine. The html output looks like this:

<link href="../../App_Themes/Default/BaseStyleSheet.css?t=20140228192910" type="text/css" rel="stylesheet" />
<link href="../../App_Themes/Default/NonConvert.css?t=20140228175530" type="text/css" rel="stylesheet" />

When I add a button and do a postback, this is my html output:

<link href="../../App_Themes/Default/BaseStyleSheet.css?t=20140228192910" type="text/css" rel="stylesheet" />
<link href="../../App_Themes/Default/BaseStyleSheet.css?t=20140228192910" type="text/css" rel="stylesheet" />

What am I missing? Do I have to remove the querystrings before the viewstate saves?

Answer 1

I have a same issue with you. Finally I found a way to fixed it. Maybe you can try disable link's viewstat as follows:

link.EnableViewState = false