How to increment a variable in ASP.NET (C#) between page views or button clicks

Question

I have the feeling that i'm missing something key here.

I've tried following guides on http://msdn.microsoft.com/en-us/magazine/cc300437.aspx and on google, but i can't see what i haven't done.

I have some very basic code which i have written just trying to get this to work:

The Default.aspx code:

<%@ Page Language="C#" AutoEventWireup="true" CodeFile="Default.aspx.cs" Inherits="_Default" EnableSessionState="True" %>

<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd">

<html xmlns="http://www.w3.org/1999/xhtml">
<head runat="server">
    <title>Demo Page</title>
</head>
<body>
    <form id="form1" runat="server">
    <div>
        <asp:Label ID="myLabel" runat="server" Text="foo"></asp:Label>
        <asp:LinkButton ID="lnkClickButton" runat="server" OnClick="lnkClickButton_Click" CommandName="Clicky">Click Me</asp:LinkButton>
    </div>
    </form>
</body>
</html>

The Default.aspx.cs code:

using System;
using System.Collections.Generic;
using System.Web;
using System.Web.UI;
using System.Web.UI.WebControls;

public partial class _Default : System.Web.UI.Page
{
    protected void Page_Load(object sender, EventArgs e)
    {
        Session["clickcount"] = 0;
        Cache["clickscount"] = 0;
    }
    protected void lnkClickButton_Click(object sender, EventArgs e)
    {
        Session["clickcount"] = (int)Session["clickcount"] + 1;
        Cache["clickscount"] = (int)Cache["clickscount"] + 1;

        Label myLabel = ((Label)this.FindControl("myLabel"));
        if (myLabel != null)
        {
            myLabel.Text = "Session: " + Session["clickcount"] + "; Cache: " + Cache["clickscount"] + ";";
        }
    }
}

I've tried using both the session object and the cache object to increment the values, but to no avail. I just get 1 every time.

N.B. this is my first asp.net project, also i'm fairly new to c#.

So many useful points from you all. I want to accept more than one answer, unfortunately i can't — m3z
– m3z, Commented May 28, 2012 at 10:26

m3z · Accepted Answer · 2012-05-28 10:32:38Z

6

Page_Load is ran every postback as well as the initial load. You need to specify no postback in your Page_Load:

protected void Page_Load(object sender, EventArgs e)
{
    if (!Page.IsPostBack){
       Session["clickcount"] = 0;
       Cache["clickscount"] = 0;
    }
}

Better still, specify that it should only be set if it doesn't already have a value:

protected void Page_Load(object sender, EventArgs e)
{
    if (Session["clickcount"] == null){
       Session["clickcount"] = 0;
    }
}

Just to clarify, the reason that it is better to only set the value if it isn't already set is that Page.IsPostBack is false every time someone directly visits the page. Say for instance you have your page http://example.com/Demo/Default.aspx and at the top you have a logo which you wrap in logo here, the session would be reset every time somebody clicked on the logo, even though they didn't actually leave the page. Also happens if they refresh on their browser without re-posting the last post.

edited May 28, 2012 at 10:32

m3z

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answered May 28, 2012 at 10:08

Curtis

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2 Comments

m3z Over a year ago

thanks, knew i was being silly somewhere. I had kinda assumed that was a constructor and was run once. Silly Me - I'll accept your answer when it lets me cos its got the most detail

m3z Over a year ago

I've edited your answer for anyone else looking for this. Hopefully it will be helpful

Pranay Rana · Accepted Answer · 2012-05-29 11:36:52Z

4

Read on MSDN : Page.IsPostBack Property - Gets a value that indicates whether the page is being rendered for the first time or is being loaded in response to a postback.

vlue of property is true if the page is being loaded in response to a client postback; otherwise, false.

code like this ...you need to put the code in !IsPostBack as like below

protected void Page_Load(object sender, EventArgs e)     
{
     if(!IsPostBack)
    {
         Session["clickcount"] = 0;
         Cache["clickscount"] = 0;
    }
 }

serverside control generate postback to page it self so the code that you dont wnat to execute on each postbck need to be put as above

this will resolve your issue easily...

further to this you can create static property for count like this

Check my post on : Programming Practice for Server Side State Maintenance Variable

private int ClickCount
{
  get 
   {
     if (Session["clickcount"] == null)
     {         Session["clickcount"] = 0; return 0;      }
     else 
        return (int)Session["clickcount"] ; 
   }
   set
   {
      Session["clickcount"] = value;
   }
}

than in final code

protected void Page_Load(object sender, EventArgs e)     
{
         if(!IsPostBack)
        {
            ClickCount = 0; 
        }
}

protected void lnkClickButton_Click(object sender, EventArgs e)
{
              int val = ClickCount ;
              ClickCount  = val + 1; 
}

edited May 29, 2012 at 11:36

answered May 28, 2012 at 10:09

Pranay Rana

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3 Comments

m3z Over a year ago

Just tried the static property, you can't access session from within a static property, but if you make it non static it works. Edited your post to reflect this

Pranay Rana Over a year ago

@MMM - its working fine check my post ... pranayamr.blogspot.com/2011/01/…

m3z Over a year ago

Hi Pranay, your post doesn't use the static keyword either.

Blachshma · Accepted Answer · 2012-05-28 10:14:24Z

1

Writing:

Session["clickcount"] = 0;

In the Page_Load will cause the counter to be reset every time the user enters the page.

Seems to me you want something like this:

protected void lnkClickButton_Click(object sender, EventArgs e)
{
    if (Session["clickcount"] == null)
    {
            Session["clickcount"] = 1;
    }
    else
    {
           Session["clickscount"] = (int)Session["clickscount"] + 1;
    }

    Label myLabel = ((Label)this.FindControl("myLabel"));
    if (myLabel != null)
    {
        myLabel.Text = "Session: " + Session["clickcount"] + "; 
    }
}

answered May 28, 2012 at 10:14

Blachshma

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Comments

stay_hungry · Accepted Answer · 2012-05-28 10:51:50Z

1

You get 1 because every post back your session and cache variable equal to 0.

protected void Page_Load(object sender, EventArgs e)
{
    Session["clickcount"] = 0;
    Cache["clickscount"] = 0;
}

And button click occur after the page_load, So you should use IsPostback property.

 protected void Page_Load(object sender, EventArgs e)

{

 if(!IsPostBack)
{
     Session["clickcount"] = 0;
     Cache["clickscount"] = 0;
}

}

Now these variables initialize only when page is loaded.

You should go through following link. It is described Asp.net page life.

http://msdn.microsoft.com/en-us/library/ms178472.aspx

answered May 28, 2012 at 10:51

stay_hungry

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