ASP.Net ViewState and InitializeCultu re

[Telinstryata]

Is there a way to read the ViewState by using Request.Form("_ _VIEWSTATE")? I want to read a value from the ViewState during the InitializeCultu re function, but the ViewState object isn't initialized until after the Init portion of the ASP.Net Page Life Cycle. The following code always crashes once the Session times out, because the ViewState is always Nothing until after the Init portion.

    Public Property CurrentUICulture() As String
        Get
            Return ViewState(CURRENT_UI_CULTURE)
        End Get
        Set(ByVal value As String)
            ViewState(CURRENT_UI_CULTURE) = value
        End Set
    End Property
 
Protected Overrides Sub InitializeCulture()
        If Session(CURRENT_UI_CULTURE) Is Nothing Then
            ' If not read from the VS
            Thread.CurrentThread.CurrentUICulture = New CultureInfo(CurrentUICulture)
            Session(CURRENT_UI_CULTURE) = CurrentUICulture
        Else
            ' If so, read from the Session
            Thread.CurrentThread.CurrentUICulture = New CultureInfo(Session(CURRENT_UI_CULTURE).ToString)
            CurrentUICulture = Session(CURRENT_UI_CULTURE)
        End If
        Thread.CurrentThread.CurrentCulture = Thread.CurrentThread.CurrentUICulture
End Sub
 

[Frinavale]

What are you doing here:

 Public Property CurrentUICulture() As String
         Get
            Return ViewState(CURRENT_UI_CULTURE)
         End Get
         Set(ByVal value As String)
             ViewState(CURRENT_UI_CULTURE) = value
         End Set
     End Property
 

You can retrieve the Current UI Culture from the current thread.


Please see my comments in the following code:

Protected Overrides Sub InitializeCulture()
         If Session(CURRENT_UI_CULTURE) Is Nothing Then
             ' If not read from the VS
 
'Don't do this...........Why are you doing this????
             Thread.CurrentThread.CurrentUICulture = New CultureInfo(CurrentUICulture)
 
             Session(CURRENT_UI_CULTURE) = CurrentUICulture
         Else
             ' If so, read from the Session
             Thread.CurrentThread.CurrentUICulture = New CultureInfo(Session(CURRENT_UI_CULTURE).ToString)
             CurrentUICulture = Session(CURRENT_UI_CULTURE)
         End If
 
'What is the point of this??????
         Thread.CurrentThread.CurrentCulture = Thread.CurrentThread.CurrentUICulture
 End Sub
 

-Frinny

[Telinstryata]

Basically, I need to create a website that is available in both English and French.

1. The user is started with a page that lets them choose their preferred language.
2. Once in the application they can switch their language and all it does is switch the language of their current page.

Currently, I store the selected language is a Session variable and then set the culture of the page to their selected language, so that the correct Resource files for the language are used. If they switch languages then I change the Session variable to the opposite language and to a redirect back to the current page. As long as the Session doesn't expire this works fine, but this fails when the Session times out. I need some way to save their selected language, without using Cookies, so that if the Session times out, I can still find out what language they had selected and not force them to choose their language again. I was hoping to use the ViewState to store the selected language, but ViewState is unavailable in InitializeCultu re, because it hasn't been initialized by that point in the process.

[Frinavale]

I hate to tell you this but in order to use Session you are already setting a Cookie....

Also, storing the user's preference in ViewState will not work no matter how much you wish it would....as you already know, ViewState is loaded after the InitializeCultu re event and so this technique will always fail.. That's just how things work. So you need to find another way to store your user's preference....t hat's why cookies are commonly used for this purpose.

Anyways, I've managed to implement a quick solution to your problem that doesn't use cookies and reduces a whole Response.Redire ct....which I kind of like.

The solution involves using JavaScript to set an hidden field to the language that the user has selected. You can then retrieve this value through Request.Params( ) to determine the language to set the page to.


Place a hidden field in your ASPX page:

<asp:HiddenField ID="languagePreference" runat="server" />

Also place the following JavaScript code in your ASPX page:

 <script type="text/javascript">
       function loadLanguage(langCode)
       {
         /*setting the hidden field's value to be the language code the user picked*/
         document.getElementById('<%= languagePreference.ClientID %>').value=langCode;
         return true;
       }
 
      function setName()
      {  
         /*setting the Name of the hidden field so that we can retrieve it on the server using Request.Params()*/
        document.getElementById('<%= languagePreference.ClientID %>').name='languagePreference';
       }
    </script>
 

You need to call the setName JavaScript function in your <body> tag's onload event. This function sets the hidden field's "name" so that you can retrieve it's value using the Request.Param() on the server. If you don't set this, the name will be set to the same thing as the hidden field's ClientID....whi ch is unobtainable in the InitializeCultu re event.

<body onload="setName()">

Set the OnClientClick in your buttons to call the JavaScript, passing it the language code you want display the page in. I used LinkButtons when implementing this solution...but it's the same idea if you are using regular buttons.

 <asp:LinkButton ID="French" Text="French" runat="server" 
        meta:resourcekey="FrenchResource1" OnClientClick="return loadLanguage('fr');"></asp:LinkButton>
    <asp:LinkButton ID="English" Text="English" runat="server" 
        meta:resourcekey="EnglishResource1" OnClientClick="return loadLanguage('en');"></asp:LinkButton>
 

Now in your InitializeCultu re method all you have to do is the following:

    Protected Overrides Sub InitializeCulture()
        Dim languagePref As String = Request.Params("languagePreference")
        If String.IsNullOrEmpty(languagePref) = False Then
            Thread.CurrentThread.CurrentUICulture = New CultureInfo(languagePref)
        End If
    End Sub
 

You don't even have to put any server side implementation for your button click events! There's no need to do a Response.Redire ct because everything's already set :)

It just loads the page using the language you specified right in the InitializeCultu re method :)

Please note that it will use the default resource if no language is specified.

One last thing, you have to set the hidden field's value to the language code in the PreRender or else the value will be lost.

  Private Sub _Default_PreRender(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.PreRender
 
        languagePreference.Value = Thread.CurrentThread.CurrentUICulture.ToString
  End Sub
 

Cheers!

-Frinny

[Telinstryata]

Thank you very much for the work you put into this.

I was sort of hoping that I would be able to come up with a solution that I can place in a base class and everything would be handled automatically. So, no JS function calls needed on every link/button, no hidden fields on every page. It's really a catch 22. If I put my code in the PreLoad the ViewState can be read, but by that point it's too late to set the culture. If I put it in the InitializeCultu re it's too early because there's no ViewState yet. I need something in between where I can set (or reset) the culture after the ViewState becomes available.

I guess I should have stated that I was hoping to avoid manual cookies, I'm fully aware that sessions use cookies, but, you know, out-of-sight out-of-mind.

I'm not going to give up on this, and if I find anything I'll be sure to post it back here.

[Frinavale]

Thank you very much for the work you put into this.

I was sort of hoping that I would be able to come up with a solution that I can place in a base class and everything would be handled automatically.

If youo have to override the InitializeCultu re event in every ASPX page, implementing a base class for all the Pages in your project that has the InitializeCultu re event defined it may be really helpful.

So, no JS function calls needed on every link/button, no hidden fields on every page.

You don't need to apply the JS calls to every link button on the page.......just the link buttons that change the language....and you only have 2: English and French.

And you can place the hidden field in the MasterPage if you want.
Just be aware that you wont be able to access it in the VB code for your master page to set it's value in the PreRender event...so you'll have to come up with another way to set it...ie add it to the setName JavaScript function.

2. Once in the application they can switch their language and all it does is switch the language of their current page.

According to this requirement you don't even need to remember the language preferences between pages in your site.......so you don't even need to store it in Session.......n or do you even need to put the hidden field in the master class...because every page's settings are unique.

It's really a catch 22. If I put my code in the PreLoad the ViewState can be read, but by that point it's too late to set the culture.

So this obviously wont work.

If I put it in the InitializeCultu re it's too early because there's no ViewState yet.

So, don't use ViewState....

I need something in between where I can set (or reset) the culture after the ViewState becomes available.

This doesn't exist.

I guess I should have stated that I was hoping to avoid manual cookies, I'm fully aware that sessions use cookies, but, you know, out-of-sight out-of-mind.

Cookies really are your friend here if you're not willing to use a hidden field.

[Rodo]

Nice trick Frinny !
Changing language without redirect and loose viewstate... is great.
thanks

[Frinavale]

I'm glad it was helpful for you :)