Can't detect whether Session variable exists

Question

I'm trying to determine if a Session variable exists, but I'm getting the error:

System.NullReferenceException: Object reference not set to an instance of an object.

Code:

    // Check if the "company_path" exists in the Session context
    if (System.Web.HttpContext.Current.Session["company_path"].ToString() != null)
    {
        // Session exists, set it
        company_path = System.Web.HttpContext.Current.Session["company_path"].ToString();
    }
    else
    {
        // Session doesn't exist, set it to the default
        company_path = "/reflex/SMD";
    }

That is because the Session name "company_path" doesn't exist, but I can't detect it!

score 37 · Accepted Answer · answered Oct 19 '12 at 10:09

37

Do not use ToString() if you want to check if Session["company_path"] is null. As if Session["company_path"] is null then Session["company_path"].ToString() will give you exception.

Change

if (System.Web.HttpContext.Current.Session["company_path"].ToString() != null)
{
    company_path = System.Web.HttpContext.Current.Session["company_path"].ToString();
}
else
{
    company_path = "/reflex/SMD";
}

To

if (System.Web.HttpContext.Current.Session["company_path"]!= null)
{
      company_path = System.Web.HttpContext.Current.Session["company_path"].ToString();
}
else
{
      company_path = "/reflex/SMD";
}

answered Oct 19 '12 at 10:09

Adil

146,340
25
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204

Thanks for the answer, I'm still getting the same error though with that – Luke Oct 19 '12 at 10:11
1

Check if your current thread can access System.Web.HttpContext? – Adil Oct 19 '12 at 10:12
1

How do I check that? I have `using System.Web`? Is this right? – Luke Oct 19 '12 at 10:15
Is it your aspx page code behind or some class in your library? – Adil Oct 19 '12 at 10:16
It's a class in my App_Code folder. Is there a special way that I need to give it access? I want to avoid having to pass the variable in my constructor. Thanks :) – Luke Oct 19 '12 at 10:16
You can access in App_Code. I confirmed it by test again. – Adil Oct 19 '12 at 10:31

score 3 · Answer 2 · answered Oct 04 '18 at 09:22

This can be solved as a one liner in the latest version of .NET using a null-conditional ?. and a null-coalesce ??:

// Check if the "company_path" exists in the Session context
company_path = System.Web.HttpContext.Current.Session["company_path"]?.ToString() ?? "/reflex/SMD";

Links:

https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-coalescing-operator https://learn.microsoft.com/en-us/dotnet/csharp/language-reference/operators/null-conditional-operators

score 0 · Answer 3 · answered Aug 12 '17 at 12:36

0

If deploying on Azure (as of August 2017), it is useful to also check if the Session keys array is populated, e.g.:

Session.Keys.Count > 0 && Session["company_path"]!= null

answered Aug 12 '17 at 12:36

Manish

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29

Can't detect whether Session variable exists

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