Question

I tried to post the selected ID number from source page into a new target page(pop up window) and display more details on that page.

I have googled the varies solutions but seem like they are a bit out of date.
Here are my questions:

What’s the best way to post it (session? cookie?) or Page.PreviousPage.FindControl? or add a control into <ItemTemplate>? or Javascript?

I don’t want to use a query string since I don’t want the user to manually modify it.

What should I write on the target page to grab that value?

protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
{
    string testID= GridView1.SelectedRow.Cells[3].Text;
    // eg. Session["ID"] = testID;

    //eg. open new pop up window ("target.aspx");
}

Many thx

Answer 1

Although you could use store your selected value on a session variable or even cross-page postbacks, my preferred method and overall standard method is to use a simple querystring value.

1) Grab the value and redirect with the desired ID.

 protected void GridView1_SelectedIndexChanged(object sender, EventArgs e)
    {    
        var testID = gridView1.SelectedRow.Cells[3].Text;
        Response.Redirect("target.aspx?Id=" + Server.UrlEncode(testID));
    }

2) On the “target.aspx” page, load the values from the url (“http://localhost/target.aspx?Id=125“)

  protected void Page_Load()
    {
        if (!IsPostBack)
        {
            var querystringValue = Request.QueryString["Id"];
            if (!string.IsNullOrEmpty(querystringValue))
            {
                // do something.
            }
        }
    }

Passing variables between pages using QueryString.

Edit: Although I wouldn’t do such a thing (I like to keep my websites as stateless as possible), the same principle applies to session variables.

protected void Page_Load()
    {
        if (!IsPostBack)
        {
            var sessionValue = Session["Id"];
            if (!string.IsNullOrEmpty(sessionValue))
            {
                // do something.
            }
        }
    }

That being said, I don’t understand what’s the problem with querystrings. Sure, the user can modify it and insert bogus values, but that’s where your server-side validations come into place. And hey, if google uses querystrings, they can’t be all that bad.