This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 6 years ago.
I have a program in which I keep getting the NullReferenceException error. Here is the code that is causing the error:
string description = "";
if (string.IsNullOrEmpty(eventItem.Description.ToString()))
{
description = "No description available.";
}
else
{
description = eventItem.Description.ToString();
}
I have looked through this post (What is a NullReferenceException and how do I fix it?), and I have tried several of the solutions (I'm afraid I simply don't understand all of them enough to try them), but I just can't figure out why this is happening. In my understanding, this error occurs because the string is in fact null.
There are events on my Google Calendar that have no description entered, so the description is null, but shouldn't the code I have check for that, and handle it? Or, is the problem that eventItem.Description.ToString() cannot be null when I call the IsNullOrEmpty method? I have also tried changing the if statement to this:
if (eventItem.Description.ToString() == null)
...but I still get the NRE error. I have tried rewriting my code so many different ways, but nothing has worked. I'm at the end of my rope!
Your eventItem itself may be null. Do something along the lines
if ( eventItem!= null && eventItem.Description != null && eventItem.Description.ToString() == null)
Updated after DStanley pointed out in the comment that .ToString() == null comparison would be unnecessary.
if ( eventItem!= null && eventItem.Description != null)
{
}
Just to help you understand a little better... NullReferenceException basically means you are trying to use some object without instantiating it. One of the simplest way to prevent is to add a null check if you are not sure whether the object is not null. And when I say adding a null check, it simply means comparing to null in the if block before accessing any property of the object.
if( objectName != null)
{
//then do something on the object
}
shouldn't the code I have check for that, and handle it?
Not if item or item.Description is null. If item is null then the call to .Description will throw a null reference exception, and if item.Description is null then the call to ToString will throw a null reference exception. There's no "magic" that lets you call ToString on a null reference.
Note that if item.Description is already a string then there's no need to call ToString(). just do:
if (string.IsNullOrEmpty(eventItem.Description))
{
description = "No description available.";
}
else
{
description = eventItem.Description;
}
Related
This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 7 months ago.
I have below code.
var cfg = _cfgUtil.GetCCfg(addr.Cnt, li.txDte);
if (cfg != null && cfg.Isabc)
{
await <some operation>
}
it is failing in second line
if (cfg != null && cfg.Isabc)
what Im not getting is , how to bypass this NUll reference check
exact error Im getting is :
System.NullReferenceException: 'Object reference not set to an
instance of an object.'
I would say your Isabc is what has the null value.
That would need checking also, cfg.Isabc != null
Alternatively, if you are using a newish version of C# the folowing would work, without needing separate checks.
// Option A:
if(cfg != null && cfg.Isabc != null)
{
//...
}
// Option B:
if(cfg?.Isabc is not null)
{
//...
}
This all assumes Isabc is of type bool?, since normally a bool wouldn't be null and other types wouldn't work that way in the if statement.
This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 6 years ago.
I'm a bit confused here (undoubtedly due to being new to C# and entity framework but that's besides the point) I want to check for a situation where my query to the database returns no data and upon that happening set some values to variables on my page Below is the code I have up right now which is throwing an error telling me that I need to check for null on the very line where I am checking for null (if the UserName value is null the record was not returned as it is a required column). So what am I missing on how to go about checking for null return here?
using (CInTracDBEntities Context = new CInTracDBEntities())
{
var CInTracUsers = Context.CInTracUsers.Where(a => a.Login == HttpContext.Current.Request.LogonUserIdentity.Name).Select(x => new { x.Login, x.UserName, x.Status, x.StatusDate, x.ReviewDate }).FirstOrDefault();
if (CInTracUsers.UserName == null)
Thanks,
Ken....
ask for the whole object:
if (CInTracUsers == null)
because if CInTracUsers is null you'll get an exception when calling any of his proprties
This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 8 years ago.
i am applying the multiple search option on a single table ..
for that i have made a sp which is accepting 3 value
.
my problem is if i apply the multiple search on the table it is taking only one search value at a time
so i used view state
if (ViewState["gen"] != null || ViewState["cen"]!=null)
{
var a = db.sp_StudentSelect1(ViewState["gen"].ToString(), ViewState["cen"].ToString());
GridView1.DataSource = a;
DataBind();
}
but it is giving me an error
Object reference not set to an instance of an object.
Description: An unhandled exception occurred during the execution of the current web request. Please review the stack trace for more information about the error and where it originated in the code.
Exception Details: System.NullReferenceException: Object reference not set to an instance of an object.
please help...
You want and not or in your if statement:
if (ViewState["gen"] != null && ViewState["cen"]!=null)
Right now just one of them can be non-null and the if statement will pass, but if one of them is null then the statement inside the if won't work because you can't call ToString() on a null value. Use && as above. Or you can edit your code to not fail if one of the values is null (by passing an empty string or some other default value.)
HERE IS AN EXAMPLE HOW TO "FIX" the code:
string gen, cen;
gen = "Default";
cen = "Default";
if (ViewState["gen"] != null)
gen = ViewState["gen"];
if (ViewState["cen"] != null)
cen = ViewState["cen"];
var a = db.sp_StudentSelect1(gen,cen);
GridView1.DataSource = a;
DataBind();
As per Hogan's answer if all parameters are mandatory then use && plus use this check before binding in case your stored procedure returns no rows or null
This indicates var a has null value.
before assigning the datasource do this check
if(a!=DBNull.Value)
{
GridView1.DataSource = a;
DataBind();
}
Does it work when you pass one parameter from ViewState?
Also where you do you store values in ViewState? (i.e. what method page_load?)
Every post I have found suggests that this happens when there is a null value. I have tried examples such as one found here but no matter what I seem to try I still end up with the same error message.
Does anyone have any idea of what the case could be?
var aaresults1 = (from a in db.AAs
where a.AAID == aaid.AAID & a != null
select a);
Reading through other StackOverflow posts about this error, it appears to happen when a where clause refers to a value that is null. Based on that, I'm guessing that your aaid object is null when you run this.
var aaresults1 = db.AAs.AsQueryable();
if(aaid != null)
{
aaresults1 = aaresults1.Where(a => a.AAID == aaid.AAID);
}
I am sure this is a case of basic ignorance, but I'm trying to test a database value using code behind in a Lightswitch project.
I'm checking if a varchar(MAX) value is null
if (Order.OrderNotes.Equals(null))
{
do.something...
}
However, I get a NullReferenceException if the value is null. If a value is there I get no error. I've tried using .contains(null), .Length = 0, .ToString() = "" etc without luck. It seems that ints and dates work fine using Equals(null), but not it seems for a string.
Help!!
Assuming you're calling this from a details screen where Order != null as #DeeMac pointed out.
You can check that Order isn't null using the same code below :
if (Order.OrderNotes == null)
{
// do.something...
}
if OrderNotes is null, you can't call any method, properties or whatever using that instance
you should call
if (Order.OrderNotes == null)
of course I assume that the var Order is not itself null,
if you want to be absolutely sure you could change your test in this way
if (Order != null && Order.OrderNotes == null)
In LightSwitch, to test if a nullable property has a value or not, you can use HasValue, so:
"if Order.OrderNotes.HasValue"
If you want the value if there is one, or the default value for the property type, you can use GetValueOrDefault:
"var value = Order.OrderNotes.GetValueOrDefault"
I agree wholeheartedly with Steve that you should be doing null checking on objects (such as Order) before trying to get a value from any of that object's properties.