not working viewstate in asp

Question

In my ASP.NET Web Application, I have a "Next" button control. Each time I click this button, I want the value of ViewState["QNO"] to increase by 1.

protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
            int qno = Convert.ToInt32(ViewState["QNO"]);
            if (ViewState["QNO"] == null)
            {
                ViewState["QNO"] = 1;
            }
            else
            {
                ViewState["QNO"] = qno++;
            }
        }

Code for click event on button:

protected void btnNext_Click(object sender, EventArgs e)
    {

        SqlConnection con = new SqlConnection(str);
        con.Open();
        SqlCommand cmd = new SqlCommand("select * from QSet where QID='" + ViewState["QNO"] + "'", con);
        SqlDataReader dr = cmd.ExecuteReader();
        if (dr.Read())
        {
            lblNo.Text = "(" + dr.GetValue(0).ToString() + ")";
            lblQues.Text = dr.GetValue(1).ToString();
            Qoptions.Items.Add(dr.GetValue(2).ToString());
            Qoptions.Items.Add(dr.GetValue(3).ToString());
            Qoptions.Items.Add(dr.GetValue(4).ToString());
            Qoptions.Items.Add(dr.GetValue(5).ToString());
        }

        con.Close();
    }

Answer 1

Change your code for Page Load as this:

   protected void Page_Load(object sender, EventArgs e)
    {
        if (!IsPostBack)
        {
                ViewState["QNO"] = 1;
        }
        else
         {
             ViewState["QNO"] = Convert.ToInt32(ViewState["QNO"]) +1;
         }
}

Answer 2

I believe a server side button click causes a PostBack. In your code, you have if (!IsPostBack) then increment by 1. Change to if (IsPostBack) perhaps.

Answer 3

code inside if (!IsPostBack) will only be hit on initial load.

change load code to

if (IsPostBack)
    {
        if (ViewState["QNO"] == null)
        {
            ViewState["QNO"] = 1;
        }
        else
        {
            int qno = Convert.ToInt32(ViewState["QNO"]);
            ViewState["QNO"] = qno++;
        }
    }

Answer 4

The problem is with the assignment of the increment operator. Also, I made few corrections.

    public void IncrementQNO()
    {
        if (ViewState["QNO"] == null)
        {
            ViewState["QNO"] = 1;
        }
        else
        {
            int qno = Convert.ToInt32(ViewState["QNO"]);
            ViewState["QNO"] = ++qno;
        }
    }

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

Just tested this and it works fine.

Answer 5

In your page_load, this line will fail right away:

int qno = Convert.ToInt32(ViewState["QNO"]);

The code is not running in a postback, so anything you pull out of viewstate will, by definition, be null.

You need another code path to initialize "QNO" with 0 if not in postback.