Firefox refresh viewstate updatepanel bug hell!!!

Have you ever noticed that when you click the Refresh button in Firefox, any form values you have filled in on the screen are retained after the refresh? Firefox is automatically altering these values at the end of the request, presumably as a convenience to you, the user. Hence the DOM and the page source are out of sync immediately after the refresh. There is nothing you can do to disable this behaviour within Firefox.

For the average web app, this is a desirable feature. But when combined with the ASP.Net viewstate model, it is anything but desirable, as ASP.Net uses a hidden form field to store serialized viewstate information.

The specific bug I have encountered is when using ASP.Net in conjunction with the built-in validation controls and AJAX. When using validation controls, if viewstate does not match that which last left the server, an error is produced :

The state information is invalid for this page and might be corrupted.

Because Firefox attempts to fill in the current form with current values after a refresh, a new viewstate, representing a fresh page, can be overwritten by an old viewstate (the result of 1 or many AJAX postbacks changing control states since the last "fresh" page load.)

The easiest solution I have found to this problem thus far is to change the form ID with each (non postback) page load. This will fool Firefox into thinking the form is different, and as such all values (including viewstate) will get their values from the incoming HTML rather than the browser's previous state.

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load

    If Not Me.IsPostBack Then

        Me.form1.ID = "form" & Date.Now.Ticks().ToString()            

    End If

End Sub

The only potential problem you could encounter with this solution is where the form ID has been hardwired in your application, either in client side script or server side code. This can be mitigated by always using myForm.clientID when referencing the form's ID. This is good practice in any case.

Hopefully this will help others having the same problems I was.

NOTE!!!
This solution will not work when using a Master Page. Use the solution suggested here instead (change form ID in pageLoaded AJAX event).

For those interested, the offending code is here in System.Web.UI.HtmlControls.HtmlForm.UniqueID: (from Reflector)

Public Overrides ReadOnly Property UniqueID As String
   Get
      If (Me.NamingContainer Is Me.Page) Then
         Return MyBase.UniqueID
      End If
      Return "aspnetForm"
   End Get
End Property

Transparent GIFs in .Net hell!!

There is a very useful article here about creating transparent gifs in .net, but there are (I think) a couple of points missing, which I'll detail here in case it saves anyone wasting a day scratching their head like I have...

GDI+ Version
It would appear that there are differences between versions 1.0 (file version 5.x) and 1.1 (6.x) of Microsoft's GDI+, in the way that they encode a non-indexed bitmap (eg 32bppARGB) into an indexed format such as Format8bppIndexed.

The problem comes with the converted palette; on my development machine (gdiplus.dll version 6.x), I appeared to be getting a custom palette based on (maybe?) the colours in the converted image (image quantization).

On a Windows 2003 server, running gdiplus.dll 5.x, I would get the standard palette as per Bob Powell's article.

This could potentially cause headaches for you if (as I did) you released a web project to production and it didn't behave as it did on your dev machine...

There appears to be very little documentation on this change between gdi+ 1.0 and 1.1, but what links I found I've added below.

Altering GIF palette
When I tried to adapt Bob's algorithm to make my gif's background transparent, I ran into a problem. Sometimes the algorithm would work, sometimes it wouldn't. At this stage, the only conclusion I can draw is that you must remove any transparent colours from the palette before attempting to set a new transparent colour... i.e, don't do this (variation of Bob's code):

'copy all the entries from the old palette removing any transparency
Dim n As Integer = 0
Dim c As Color
For Each c In cp.Entries
If n = idxToMakeTransparent Then
ncp.Entries(n) = Color.FromArgb(0, c)
Else
ncp.Entries(n) = Color.FromArgb(255, c)
End If

n += 1
Next c

're-insert the palette
bm.Palette = ncp

I think that this doesn't work if one of the colours is already defined as transparent (as seems to be the default in old gdi+ (1.0). This is all pure speculation at this point!

Good luck with your hacking.

Links
http://www.xtremevbtalk.com/t92821.html
http://support.microsoft.com/default.aspx?scid=kb;EN-US;Q319061
http://msdn.microsoft.com/library/default.asp?url=/library/en-us/dnaspp/html/colorquant.asp