ASP .NET Error as object reference not set to an instance of an object

Question

1.70/5 (3 votes)

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Hi,

I am getting the error "object reference not set to an instance of an object" while i run this piece of code, let me know what can be done to get rid of this.

C#

string cntry = Session["ddlCountry"].ToString();

            if (cntry == "US")
            {
                lnkUrl.Text = string.Empty;
                if (lnkUrl == null ||  lnkUrl.Text.Length == 0)
                {
                    lnkUrl.Text = "http://www.google.com";
                }

Posted 28-Nov-13 23:00pm

Rock_Dead

Updated 11-Mar-17 0:02am

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Comments

Richard MacCutchan 29-Nov-13 5:07am

Make sure every reference actually points to something. Also in future please show the exact line of code that gives the error.

4 solutions

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C@dER@j · Answer 1 · 2013-11-28T23:07:00

Solution 2

This is basically due to the Session object.
This is because the session is not having value i guess.
So do one thing before accessing the Session value check whether the session is exists or not. If exists then only assign this session value to variable.

Example:
Put this code in the page_Load method.First comment the Session initialization and check later on un comment and check this. Hope you will get the answer what you are searching.

C#

Session["ddlCountry"] = "US";

if (Session["ddlCountry"]!=null)
{
    string cntry = Session["ddlCountry"].ToString();

    if (cntry == "US")
    {
        lnkUrl.Text = string.Empty;
        if (lnkUrl == null || lnkUrl.Text.Length == 0)
        {
            lnkUrl.Text = "http://www.google.com";
        }
    }
}
else
{
    lnkUrl.Text="Value not present in Session.";
}

Best of luck.

Posted 28-Nov-13 23:07pm

C@dER@j

Updated 28-Nov-13 23:15pm

v2

Comments

OriginalGriff 29-Nov-13 5:24am

Reasons for my vote of one: No, it isn't.
Try this:
string s = null;
if (s == "US")
{
}
It will not throw an exception at all - so it doesn't matter if the session return value is null, it will not cause his problem

C@dER@j 29-Nov-13 5:35am

Your point is correct the code which you have written wont through ant exception. But in order to convert the null value to string using the
"string cntry = Session["ddlCountry"].ToString();"
this code throws exception. If you dint get my comment then check the difference between the function .ToString() and Convert.ToString("") then you will get to know.

Dmytro Bogachev 29-Nov-13 5:39am

Let me disagree with you. My answer is similar in Session part. And null-value Session object might be one of reasons why there is such problem. You CAN compare to null, as in your case, but here is what happens in original code:
string s = null; //Session["whatever"] is null
s.ToString(); // And exception

C@dER@j 29-Nov-13 5:50am

This is what i told.if you have null and you are going to convert to string using .tostring() then it will arise an exception. So if you are checking that null value if its not there then only you are converting using .ToString()..

OriginalGriff 29-Nov-13 5:39am

Ignore the above - I was making a coffee and realised that I had missed the "ToString" on the session access - which makes you right and me way wrong! Sorry...:O
I have corrected the vote to 5, and can only blame a Senior Moment combined with a lack of caffeine. And natural born stupidity, of course.

C@dER@j 29-Nov-13 5:46am

Ha ha ha ha h...Keep it up:-)

OriginalGriff · Answer 2 · 2013-11-28T23:07:00

Solution 1

Why are you using a property of an object, and then later checking it for null?

C#

lnkUrl.Text = string.Empty;
 if (lnkUrl == null ||  lnkUrl.Text.Length == 0)

The second text is completely useless anyway, because the previous line indirectly sets the Length to zero anyway!
Swap it over:

C#

if (lnkUrl != null)
   {
   lnkurl.Text = "http://www.google.com";
   }

And don't try to set properties of null values!

Posted 28-Nov-13 23:07pm

OriginalGriff

Comments

Rock_Dead 29-Nov-13 5:17am

I want to set the LinkURL text as http://www.google.com"; do u think this will solve the purpose?

OriginalGriff 29-Nov-13 5:27am

You can only set the value of it's Text property if lnkURL is not null - i.e. if it has been set to an instance of an object somewhere.
If the code is throwing a null reference exception when you try to access the Text property, then you need to look at the rest of your code to find out why the value has not been set yet. I can't, because you do not show that code in your fragment.
So, use the debugger to "backtrack" through your code and work out how you got there!

Rock_Dead 29-Nov-13 5:40am

I tried with this code if (lnkUrl != null)
{
lnkurl.Text = "http://www.google.com";
}
but still throws the same error

Rock_Dead 29-Nov-13 5:52am

My Link URL is null now and i want to populate the same with some text

OriginalGriff 29-Nov-13 5:40am

Ignore me - it's not that at all - it's your session as has been said already - I missed the ToString on you session access which will be throwing the exception if the session value has not been set - so look at why that is null (and check it before you try to do anything with it!)

Rock_Dead 29-Nov-13 5:46am

My session value is not coming as null, it is containing the value as expected

OriginalGriff 29-Nov-13 5:51am

How did you check?

Rock_Dead 29-Nov-13 5:56am

In the code itself while debugging, i see the value there

OriginalGriff 29-Nov-13 6:31am

And your link is null? So you need to find out why the link variable is null - where is that being set?

You can't set the link until you have set an instance of the link control into the link variable!

Dmytro Bogachev · Answer 3 · 2013-11-28T23:09:00

Solution 3

Check if you Session["ddlCountry"] has value before working with it. Check, if your lnkUrl is set to valid control.
So code might be like this:

C#

if(Session["ddlCountry"] != null)
{
    var cntry = Session["ddlCountry"].ToString();
    if (cntry.Equals("US"))
    {
        //You cannot use this control, if lnkUrl is null
        //Since you're  setting lngUrl.Text = string.Empty, it will have 
        //Text.Length == 0  in all cases; so consider changing your logic. 
        //Probably like in code below.
        if(lnkUrl != null)
        {
            if(lnkUrl.Text.Length == 0)
            {
                lnkUrl.Text = "http://www.google.com";
            }
        }
    }
}

Posted 28-Nov-13 23:09pm

Dmytro Bogachev

Updated 28-Nov-13 23:13pm

v3

Comments

Rock_Dead 29-Nov-13 5:49am

getting the same error with this code even

Dmytro Bogachev 29-Nov-13 5:53am

Did you try Debug? What is exact line of your exception? There are 2 possible points of failure in above code, Session["ddlCountry"].ToString() - if ToString() for some reason returns null (and I don't see reason for this behavior) and if lnkUrl.Text is null - this is also weird.

Rock_Dead 29-Nov-13 5:58am

i debugged it is the same exception in line lnkUrl.Text = "http://www.google.com";
and also i am changing this line i.e. if(lnkUrl != null) to if(lnkUrl == null) as the lnkUrl is coming as null

Dmytro Bogachev 29-Nov-13 6:00am

So your problem is not in above code, it is correct. Show please code, where you're getting lnkUrl. Basically it's about this control.

Rock_Dead 29-Nov-13 6:01am

I have not set text value in this Linkurl. this is the code

<asp:LinkButton ID="lnkUrl" runat="server" CssClass="linkurl" ForeColor="#006600"
Font-Bold="True" Font-Names="Verdana" Font-Size="8pt">

Dmytro Bogachev 29-Nov-13 6:04am

One of possible reasons - this control is not yet initialized. What is the event (Page event), in which you're having code, that throws exception?

Rock_Dead 29-Nov-13 6:11am

On Page Load

Dmytro Bogachev 29-Nov-13 7:05am

There is something we're missing about your question. Control should be initialized already on Page_Load. Maybe you're using Custom Controls and your link button is in custom control, maybe there is some issue about cache, if you use it, but anyways it is not about code you posted here. I suggest you open new question with brief description of your current page structure, which will ask, why lnkUrl is null during Page_Load event.

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) · Answer 4 · 2013-11-28T23:15:00

Solution 4

Before reading Session, always check for null.

C#

if(Session["ddlCountry"] != null)
{
    string cntry = Session["ddlCountry"].ToString();
}

If Session ddlCountry value is not present, it will throw "Object reference exception".

Posted 28-Nov-13 23:15pm

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ)

Comments

N.Manjula 13-Feb-16 5:38am

I have Copied the code but I get an error Invalid MAshape key even i have pasted testing key

Tadit Dash (ତଡିତ୍ କୁମାର ଦାଶ) 15-Feb-16 2:22am

I am not getting. What are you trying to do?