How to avoid "Response.Redirect cannot be called in a Page callback"

Question

I'm cleaning up some legacy framework code and a huge amount of it is simply coding by exception. No values are checked to see if they are null, and as a result, copious amounts of exceptions are thrown and caught.

I've got most of them cleaned up, however, There are a few error / login / security related framework methods that are doing Response.Redirect and now that we are using ajax, we are getting ALOT of "Response.Redirect cannot be called in a Page callback." And I'd like to avoid this if at all possible.

Is there a way to programatically avoid this exception? I'm looking for something like

if (Request.CanRedirect)
    Request.Redirect("url");

Note, this is also happening with Server.Transfer, so I'd like to be able to check if I am able to do Request.Redirect OR Server.Transfer.

Currently, its simply doing this

try
{
    Server.Transfer("~/Error.aspx"); // sometimes response.redirect
}
catch (Exception abc)
{
    // handle error here, the error is typically:
    //    Response.Redirect cannot be called in a Page callback
}

Answer 1

You can try

if (!Page.IsCallback)
    Request.Redirect("url");

or if you dont have a Page handy...

try
{
    if (HttpContext.Current == null)
     return;
    if (HttpContext.Current.CurrentHandler == null)
     return;
    if (!(HttpContext.Current.CurrentHandler is System.Web.UI.Page))
     return;
    if (((System.Web.UI.Page)HttpContext.Current.CurrentHandler).IsCallback)
     return;

    Server.Transfer("~/Error.aspx");
}
catch (Exception abc)
{
    // handle it
}

Answer 2

You should load up your ScriptManager or ScriptManagerProxy, and then check the IsInAsyncPostBack flag. That would look something like this:

ScriptManager sm = this.Page.Form.FindControl("myScriptManager") as ScriptManager;
if(!sm.IsInAsyncPostBack)
{
    ...
}

By doing this, you can mix async postbacks (which should fail to redirect) with normal postbacks, which I'm assuming you still want to redirect.