Response is not available in this context when using System.Timers.Timer in asp.net

Question

I am attempting to redirect a user to a different page when a timer elapsed. My code runs but I get this error on this line

Page.Response.Redirect(myUri, false);

my code looks like this

void dataSyncCheck_Elapsed(object sender, System.Timers.ElapsedEventArgs e) {
  Page.Response.Redirect(myUri, false);
}

Answer 1

            var tasks = new Task[2]
            {
                Task.Factory.StartNew(() => {
                   //Process Data
                }),

                Task.Factory.StartNew(() => {
                    //Sleep while not sync.
                })
            };

            Task.WaitAll(tasks);

Page.Response does not exist after the client has finished loading the page. Therefore cannot be used to redirect after the fact.

You can do the above and force the page load to wait for the "sync check" to complete before returning a response to the client, or you can use a client side ajax request to request a status update from the server after the page is loaded essentially moving the timer from your server to the client.

Answer 2

I think the direct answer to your question is it can't be done server-side once the initial page is loaded - that is, response is sent to the client, and server-side code is out of the picture, until the next request. Such is the nature of the web.

My recommendation is to move this functionality client-side. You'll need an XmlHttpRequest (XHR, aka AJAX) call to the server (think API call, just to your own server) to determine whether or not a redirect is necessary based on your specific rules/logic. The response to such XHR call can be as simple as a boolean, or can include the URL of the redirect.

If you want to take advantage of built-in WebForms facilities to handle a client-side redirection, you can use Web.UI.Timer instead, along with a ScriptManager control:

In ASPX code:

<asp:ScriptManager ID="scriptManager" runat="server"></asp:ScriptManager>
<asp:Timer runat="server" ID="redirectTimer" Interval="5000" OnTick="redirectTimer_Tick" Enabled="true" />

In code-behind:

    protected void Page_Load(object sender, EventArgs e)
    {
        if(!IsPostBack)
        {
            //Handle initial page load
        }
    }

    protected void redirectTimer_Tick(object sender, EventArgs e)
    {
        if(someConditionIsSatisfied)
        {
            Response.Redirect(myUri, false);
        }
    }

Keep in mind, the Timer.Tick event in the above code will cause a full post-back - that is, your page will fully re-load. You can use other mechanisms, such as an update panel, to "hide" the reload from the client, but any code in your Page_Load() event handler will run on every timer tick; just be aware of that. You can ensure your Page_Load() code executes only once by checking the Page.IsPostBack property.

Bottom line, you're trying to accomplish your task in the wrong context - this is a job for the client, not the server, to handle.