Question

I have a page containing a control called PhoneInfo.ascx. PhoneInfo is dynamically created using LoadControl() and then the initControl() function is called passing in an initialization object to set some initial textbox values within PhoneInfo.

The user then changes these values and hits a submit button on the page which is wired up to the “submit_click” event. This event invokes the GetPhone() function within PhoneInfo. The returned value has all of the new user entered values except that the phoneId value (stored in ViewState and NOT edited by the user) always comes back as null.

I believe that the viewstate is responsible for keeping track of user entered data across a postback, so I can’t understand how the user values are coming back but not the explicitly set ViewState[“PhoneId”] value! If I set the ViewState[“PhoneId”] value in PhoneInfo’s page_load event, it retrieves it correctly after the postback, but this isn’t an option because I can only initialize that value when the page is ready to provide it.

I’m sure I am just messing up the page lifecycle somehow, any suggestion or questions would really help! I have included a much simplified version of the actual code below.

Containing page’s codebehind

protected void Page_Load(object sender, EventArgs e)
{
    Phone phone = controlToBind as Phone;
    PhoneInfo phoneInfo = (PhoneInfo)LoadControl("phoneInfo.ascx"); //Create phoneInfo control
    phoneInfo.InitControl(phone); //use controlToBind to initialize the new control
    Controls.Add(phoneInfo);
}
protected void submit_click(object sender, EventArgs e)
{
    Phone phone = phoneInfo.GetPhone();
}

PhoneInfo.ascx codebehind

protected void Page_Load(object sender, EventArgs e)
{
}

public void InitControl(Phone phone)
{
    if (phone != null)
    {
        ViewState["PhoneId"] = phone.Id;
        txt_areaCode.Text = SafeConvert.ToString(phone.AreaCode);
        txt_number.Text =  SafeConvert.ToString(phone.Number);
        ddl_type.SelectedValue = SafeConvert.ToString((int)phone.Type);
    }
}

public Phone GetPhone()
{
    Phone phone = new Phone();
    if ((int)ViewState["PhoneId"] >= 0)
        phone.Id = (int)ViewState["PhoneId"];
        phone.AreaCode = SafeConvert.ToInt(txt_areaCode.Text);
        phone.Number = SafeConvert.ToInt(txt_number.Text);
        phone.Type = (PhoneType)Enum.ToObject(typeof(PhoneType),       SafeConvert.ToInt(ddl_type.SelectedValue));
        return phone;
    }
}

Answer 1

I thought, like the answerers, that this problem existed because I was setting the ViewState variable too late to be saved during SaveViewState. However, I added an override for the SaveViewState event, and sure enough I was setting my ViewState variable long before the ViewState was saved. Too long before, it turns out.

Apparently after initialization, .net runs TrackViewState() which actually starts listening for any viewState variables you add. Since I had set this viewState value BEFORE TrackViewState() had run, everything appeared fine but the values were not actually being added during SaveViewState. I explicitly called TrackViewState() right before setting the variable and everything worked as expected.

My final solution was to assign a private property to hold the ID value through initialization and then to set the viewState variable during SaveViewState from the property value. This way I can ensure that TrackViewState has been run by .net without having to explicitly call it and mess up the flow of things. I reload the viewState value on page_load and use it to set the value of the property which I can then use in my GetPhone function.

This article talks about enableViewState.

private int _id = -1;

protected void Page_Load(object sender, EventArgs e)
{
    if (ViewState["PhoneId"] != null)
    _id = SafeConvert.ToInt(ViewState["PhoneId"]);
}

protected override object SaveViewState()
{
    ViewState["PhoneId"] = _id;
    return base.SaveViewState();
}

public Phone GetPhone()
{
    Phone phone = new Phone();
    phone.Id = _id;
    phone.AreaCode = SafeConvert.ToInt(txt_areaCode.Text);
    phone.Number = SafeConvert.ToInt(txt_number.Text);
    return phone;
}