How to access viewstate using javascript?

Question

I am trying to access view-state in client side but following exception coming :

JAVASCRIPT:

<script language="javascript" type="text/javascript">
    var vCode = '<%=ViewState("code")%>';
    alert(dateView);
</script>

CODE BEHIND:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    ViewState("code") = "EE"
End Sub

Anybody suggest me how to do it?

Answer 1

I would suggests to use RegisterHiddenField than mixing server/js codes:

You may try this sample:

Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles Me.Load
    ViewState("code") = "EE"
    Page.ClientScript.RegisterHiddenField("vCode", ViewState("code"))
End Sub

On your javascript:

var vCode = document.getElementById("vCode");
alert(vCode);

Answer 2

You can simply access the hidden form element that holds the viewstate.

The name of the control is __viewstate.

<input type="hidden" name="__VIEWSTATE" id="__VIEWSTATE" value="..." />

var vCode = documents.forms[0]['__VIEWSTATE'].Value;
alert(dateView);

Of course, this will give you the encrypted/encoded/compressed viewstate.

If you want specific values from it, you may find it better to record them in hidden fields and access those.

Answer 3

The Page.ClientScript.RegisterHiddenField did not work for me and returned null. You can do like this:

1-First solution: define a hidden field and make sure you set runat=server

  <input type="hidden"  id="myhiddenField" runat="server" value="" />

then in your code behind assign any value you want to it

 myhiddenField.Value= ViewState["name"].ToString();// or assign any value you want

in your javascript access it like this:

 <script type="text/javascript">  
         function test() 
              {
                var name = document.getElementById('myhiddenField').value;
                alert(name)
             }
 </script>

2-Second solution

In case for some reasons you don't want to have a server input control you can put the hidden field in a literal tag

<asp:literal id="literal1" runat="server"><input type="hidden" id="myhiddenField" value="{0}"/></asp:literal>

and then assign a value to the literal in codebehind like this

literal1.Text = string.Format(literal1.Text, "somevalue");  // somevlue can be your ViewState value

then access it in javascript as usual

   var name = document.getElementById('myhiddenField').value;
            alert(name)

Note: if you are using update panels put the hiddenfields inside the contenttemplate tag of the updatepanel