Sharepoint 2010 and Saving variables in VIEWSTATE

Question

UPDATE1

I tried with EnableViewState in Page directive: but no avail.

End

I am running as a usercontrol in sharepoint. (using SmartPart) Everything's fine. Just the Viewstate-Variables!

The usercontrol (also saving the variables in viewstate) works fine in a normal aspx-site. The issue is in a sharepoint environment it won't run. I checked the "enableViewState" is set to "true". So what can be wrong?

I am trying to extract the data(storing some text like Ids) from the ViewState but it does not seems to work and it just returns me a null value.

here is what i am doing:

UserControl Implementation (VisualWebPartControl1.cs):

WebPart Implementation (VisualWebPart1.cs)

I have created a visual web part (creates usercontrol.ascx and .cs file)

public partial class VisualWebPart1UserControl : UserControl
    {
        protected void ddl_SelectedIndexChanged(object sender, EventArgs e)
        {
            string SetId = ddl.SelectedItem.Value;
            this.ViewState[TabStorageViewStateId] = SetId; 
        }

    }

WebPart Implementation (VisualWebPart1.cs)

  public class VisualWebPart1 : WebPart
    {
        private const string _ascxPath = @"~/_CONTROLTEMPLATES/mypath/VisualWebPart1/VisualWebPart1UserControl.ascx";

        protected override void CreateChildControls()
        {
            //generated by visual studio
            //Control control = Page.LoadControl(_ascxPath);
            //Controls.Add(control);

            var control = (VisualWebPart1UserControl) Page.LoadControl(_ascxPath);

            string retValue = this.ViewState[TabStorageViewStateId] as string;

        }
    }

Answer 1

this refers to current instance of a class. So this.ViewState refers to viewstate of the control\webpart. So, logically you are wrong here as you are trying to retrieve from the place where you never stored!

Now speaking practically, Because the ViewState property is marked as protected, you can't get a control's ViewState in another.

If you want to share data between page controls per-request basis(similar to viewstate), use HttpContext.Items instead.

Answer 2

ViewState is not loaded when CreateChildControls is called so it will not be available. Please check this article for understanding of viewstate.

Answer 3

By just looking at your UPDATE1 maybe this is an answer: How to enable ViewState when developing asp.net form in web part?

By default ViewState is turned off.

To enable it you need to put EnableViewState="true" in your aspx page (Page directive) and also you need to put EnableViewState="true" in desired ContentPlaceHolder eg. PlaceHolderMain.