Clearing webform after I refresh after webpage Expires?

I have webform FillData.aspx with two textboxes, a checkbox, and a Submit button. This is the basic functionality: when I click on the checkbox, it copies the data from one textbox to the other. When I click on Submit, I redirect to page Finish.aspx. Since FillData.aspx expires immediately, when I click the "Back" button in the browser in Finish.aspx, I get the "Webpage has expired" page, which is good.
The problem is that when I refresh the page, not only do I get the data that the user had typed in, it also executes the code in CheckBox1_CheckedChanged.
My question is: How can I clear the typed text after the user refreshes when he clicks on "Back"and sees "Webpage has expired" page?
Here's my code: All my code is server-side. I also tried overriding LoadViewState and SavedViewState, but it didn't work.
protected void Page_Load(object sender, EventArgs e)
{
Response.Buffer = true;
Response.ExpiresAbsolute = DateTime.Now.Subtract(new TimeSpan(1, 0, 0, 0));
Response.Expires = -10000;
Response.CacheControl = "no-cache";
if (!Page.IsPostBack)
//Clear textboxes
}
protected void Button_complete_Click(object sender, EventArgs e)
{
Response.Redirect("Finish.aspx");
}
protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
{
if (this.CheckBox1.Checked)
// copy text from one textbox to the other.
}

Thanks.

LVL 2

MyersAAsked: 2007-11-17

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LVL 2

MyersAAuthor Commented: 2007-11-18

I was testing the checkbox and I realized that all the textboxes that were typed in after checkbox_checkedChanged are cleared when I click the Back button.
This is what happens:
1. I type something on two of the textboxes, and I click the checkbox to copy the contents to two other textboxes.
2. I type text on a fifth textbox, and I click on a server-side button which redirects me to Finish.aspx.
3. I click the back Button, and this displays the "Webpage has expired" page.
4. I refresh, and the two textboxes that were filled out before I checked the checkbox remain with the text I typed. The other three textboxes (two that were filled with checkedchanged and one that was typed in) are cleared.

Why does this happen?

Thanks.

private bool _isRefresh, _refreshState;
 
protected override void LoadViewState(object savedState)
{
    object[] allStates = (object[])savedState;
    base.LoadViewState(allStates[0]);
    _refreshState = (bool)allStates[1];
    _isRefresh = _refreshState == (bool)Session["__ISREFRESH"];
}
 
protected override object SaveViewState()
{
    Session["__ISREFRESH"] = _refreshState;
    object[] allStates = new object[2];
    allStates[0] = base.SaveViewState();
    allStates[1] = !_refreshState;
    return allStates;
}
 
 
protected void Page_Load(object sender, EventArgs e)
{
    Response.Buffer = true;
    Response.ExpiresAbsolute = DateTime.Now.Subtract(new TimeSpan(1, 0, 0, 0));
    Response.Expires = -10000;
    Response.CacheControl = "no-cache";
}
protected void Button_complete_Click(object sender, EventArgs e)
{
    Response.Redirect("OrderComplete.aspx");
    return;
    // OTHER CODE - DOESN'T GET HERE
}
protected void CheckBox1_CheckedChanged(object sender, EventArgs e)
{
    if (!_isRefresh)
    {
        if (this.CheckBox1.Checked)
        {
            this.TextBox_billAdd1.Text = this.TextBox_shipAdd1.Text;
            this.TextBox_billAdd2.Text = this.TextBox_shipAdd2.Text;
            this.TextBox_billCity.Text = this.TextBox_shipCity.Text;
            this.TextBox_billZip.Text = this.TextBox_shipZip.Text;
        }
    }
}

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LVL 1

mmq2006Commented: 2007-11-17

try adding below code within Page Load:
Response.Buffer = true;
Response.ExpiresAbsolute = DateTime.Now.Subtract(new TimeSpan(1, 0, 0, 0));
Response.Expires = -10000;
Response.CacheControl = "no-cache";
Clear Fields...

LVL 2

MyersAAuthor Commented: 2007-11-18

I'm not sure I understand what you want me to do.
I can't clear the textboxes in Page_Load (and out of the !Page.IsPostback) because they'll clear any time the page posts back. For example, the checkbox is set for autoPostBack, so the textboxes would clear out when I click on it.

LVL 1

mmq2006Commented: 2007-11-18

I meant adding below code to (!Page.IsPostBack) block.
Response.Buffer = true;
Response.ExpiresAbsolute = DateTime.Now.Subtract(new TimeSpan(1, 0, 0, 0));
Response.Expires = -10000;
Response.CacheControl = "no-cache";
Clear Fields...

also, check below link:
http://jarednevans.typepad.com/technoblog/2005/01/jareds_techno_b.html

LVL 2

MyersAAuthor Commented: 2007-11-18

The page doesn't expire if I move the code to !Page.IsPostBack. When I hit the Back button, I'll see all the data.

LVL 2

MyersAAuthor Commented: 2007-11-18

The experts-exchange credit card page also has the same problem. I just bought more points, so I entered my cc#, name, exp. date, etc... I clicked on Submit, and it took me to the Purchase Confirmation page. When I click the Back button, I can still see all my payment information. That's what I don't want.
In my case, when I click on the Back button, I get the standard "Expired Webpage" page. But if I refresh, it'll display all the information I just typed in.

Any help is appreciated. I'm using VS2005 v2.0