Easiest way to append a string with different values by checking if hiddenfields are empty

Question

I'm building an audit trail in C#, asp.net. On the .aspx page I have several hidden fields which associate themselves with regular fields (i.e. txtFirstName -> firstNameTrackerHiddenField). I have it set up so that when the user inputs/selects data to a field, the hidden field gets a value set to it. Example:

    protected void txtFirstName_TextChanged(object sender, EventArgs e)
    {
        this.FirstNameTrackerHiddenField.Value = "1";
    }

Now to build my Audit Log I was thinking of just checking through each hidden field, pulling the ones that aren't null, and appending a string, depending on which field the user has inputed/changed. I could do a bunch of nested if statements but that would be really sloppy. Sorry if I'm not making any sense, I'm still a little new to the coding world and I thought this methodology would be pretty neat and easy to implement. Here's what I have so far in the auditLog method:

    protected string auditLogString()
    {
        string auditLog = this.txtAuditLogReadOnly.Text + System.Environment.NewLine + System.Environment.NewLine + 
            DateTime.Now.ToString() + "- (Incident saved by: " + Page.User.Identity.Name + ") ";

        if (this.FirstNameTrackerHiddenField.Value != string.Empty)
        {
            auditLog += "- with changes to First Name."
            if (this.LastNameTrackerHiddenField.Value != string.Empty)
            {
                auditLog += "- with changes to Last Name."
            }
        }

        return auditLog;
    }

And the list goes on. There's about 50 fields to cycle through, so that's why I was wondering if there was a better way to go about this... Thanks for any input, and please don't be rough with me... :)

Answer 1

A cleaner way to if/else-ing every HiddenField would be to loop through the controls on your page, check their type and if they're a HiddenField with a value, do something with the value.

foreach (Control ctrl in this.Controls)
{
    if (ctrl is HiddenField)
    {
        if (!string.IsNullOrEmpty((ctrl as HiddenField).Value))
        {
            // do something
        }
    }
}