ASP.NET Stopwatch Remaining at 0

Question

So, as part of an assignment I am trying to roughly calculate the time taken for a transaction to be reviewed and completed in an ASP.NET Web Forms project using CSharp.

In my ASPX page, I am showing the details of the objects in the cart.
And there is a button which confirms the checkout and completes it.

What I need to calculate is the time since the page loaded, till the checkout was confirmed.

Here there are two events: page_load and checkoutbutton_click

So in the code behind file I am

public partial class CheckoutReview : System.Web.UI.Page
{
    public Stopwatch sw = new Stopwatch();

    protected void Page_Load(object sender, EventArgs e)
    {
        sw.Start();
        //... code
    }

    protected void checkoutbutton_click(object sender, EventArgs e)
    {
       //...code
       sw.Stop();
       // in the database i am then storing the elapsedMilliSeconds of the stopwatch
    }

The problem however is that with this code the elapsed time is remained 0 all the time. If I put the same stopwatch however in the checkoutbutton_click() the stopwatch works fine.

Can someone kindly explain what I am doing wrong here?

Answer 1

Each time the page is posted back to the server, a new instance of the class CheckoutReview is being created... so what you're seeing is the time between the creation of the class on the post-back and the event handler.

You have to remember that each request to the server (whether it's the original page request, or a post-back) is an individual call to the server. Things like Session and ViewState exist to allow you use data between those requests.

I would recommend you store the current time in the ViewState of the page on the initial load, and then check the TimeSpan difference in the event handler...

protected void Page_Load(object sender, EventArgs e)
{
  if (!Page.IsPostBack)
  {
    // Only store on first visit to the page
    ViewState["pageLoadTime"] = DateTime.Now;
  }
}

protected void checkoutbutton_click(object sender, EventArgs e)
{
  TimeSpan diff = DateTime.Now - (DateTime)ViewState["pageLoadTime"];
}