Question

I am re-writing an ASP.NET application and noticed a difference in behaviour …

In my Page_Load event I have some code such as:

string id = Request["id"]

which gets the id param from the URL. On page load (ie a HTTP GET), this works as expected in both versions. I also have a button onclick event handler. Clearly, this performs a POST to the server, and also invokes the Page_Load handler. The difference is, that in the original version of the app, the id is successfully loaded from the request. In the new version of the app, id comes back as null. I have discovered that I need to use Request.Params[“id”] instead, but am totally puzzled as to why Request[“id”] works for POST requests in one app but not the other.

The only difference between the apps is that the first was created as File -> New Website and the second File -> New Web Application. I think this is what is causing the difference in behaviour, but am wondering why this subtle difference, and also if there is anything else I should be aware of between the 2.

Any advice greatly appreciated.

Answer 1

As you have mentioned, you have the id parameter coming through twice. This will be because you have one in the query string parameters and one in the form parameters. I’m not sure why this would be occurring in one web app and not the other, but you can make changes to your code to account for it in a more correct way.

If you view the source of the HTML in your browser, you will see that the action value for the form will be current pages URL, including the query string. This is why the first id is being sent through. Evidently, the second id is coming through via the form itself:

HTML Source of basic web form

<form method="post" action="Default.aspx?id=3" id="ctl01">
    <input type="text" name="id">
</div>

There are a couple of things you can do here:

1. first off, I wouldn’t use Request.Params[“id”] for this, as it combines the query string, form, cookies and server variables into one collection. You should use Request.Querystring and Request.Form properties, based on what you require and when
2. In your Page_Load handler, use the Page.IsPostBack property to determine whether the page is loading for a GET or POST and use the Request properties described above.

Example of Page.IsPostBack usage:

protected void Page_Load(object sender, EventArgs e)
{
    string id = string.Empty;
    if (Page.IsPostBack)
    {
        id = Request.Form["id"];
    }
    else
    {
        id = Request.QueryString["id"];
    }
}