I have am iterating through a list of SharePoint list items .
A couple of items do not have data so throw the null exception.
I used
if (!string.IsNullOrEmpty(xt["ows_LinkTitle"].ToString()))
{
Entity.DefectType = xt["ows_LinkTitle"].ToString();
}
but an error still occurs.
I also tried
if(xt["ows_LinkTitle"].ToString()!= null)
{
Entity.DefectType = xt["ows_LinkTitle"].ToString();
}
I could put a try catch block around it but I don't want to do it for each and every line.
Is there any way to check the sharepoint item value without throwing an error.
Try using explicit cast instead:
Entity.DefectType = (string)xt["ows_LinkTitle"];
If you want to check for a null before assigning the value try
if(xt["ows_LinkTitle"] != null)
As .ToString() on a null is the cause of exception.
Related
Some people decided to close my previous question, but the question they linked (What is a NullReferenceException, and how do I fix it?) did not have an answer. This question is fundamentally different since the enumerable is populated. It is not null. Just as the first answer stated, I placed "strategic breakpoints" and checked the variables.
I'm debugging a XUnit test and it turns out that in my business logic the iteration variable in the foreach loop is throws an exception "Object Reference not set to instance of object". However, the list over which the iteration is happening is NOT null. I can see that when I'm debugging. Here is the code:
Business logic:
List<string> regionArray = new List<string>();
if (someCondition)
{
regionArray = _utils.GetRegions(someParam); // this is not returning null
}
foreach (var region in regionArray)
{
var query = from dataSet in myDataSets
where dataSet.Location == region
select dataSet;
var queryResult = query.FirstOrDefault();
if (queryResult == null)
{
// do stuff
} else if (queryResult.State != States.Provisioned)
{
// do stuff
}
}
Here is how I am mocking the _utils.GetRegions call, but I dont think thats the problem.
private Mock<IUtils> _mockRegionUtils;
[Fact]
public void ItWorks()
{
// do stuff
_mockRegionUtils = new Mock<IUtils>();
_mockRegionUtils.Setup(utils => utils.GetRegions(It.IsAny<ISomeParam>())).Returns(new List<string>() {"america", "china"});
// call business logic
}
I have checked all the types in the debugger. regionArray.GetType() returns {System.Collections.Generic.List`1[System.String]}. when I type region into the console however, i get:
region
'region' threw an exception of type 'System.NullReferenceException'
how is this possible?
EDIT: fixed a typo above, sorry about that. Something weird though, so if I reassign the value of regionArray to be an inline list, it still fails. But if I define a new inline list and iterate over that, the looping works fine.
List<string> regionArray = new List<string>();
if (someCondition)
{
regionArray = _utils.GetRegions(someParam); // this is not returning null
}
regionArray = new List<string>() {"china", "america"};
List<string> temp = new List<string>() {"foo", "bar"}
foreach (var region in regionArray)
{
// region still throws null reference exception
foreach (var tempVar in temp)
{
var c = tempVar; // this works. tempvar is never null.
}
var query = from dataSet in myDataSets
where dataSet.Location == region
select dataSet;
var queryResult = query.FirstOrDefault();
if (queryResult == null)
{
// do stuff
} else if (queryResult.State != States.Provisioned)
{
// do stuff
}
}
EDIT 2: So I tried iterating over the regionArray in the same way just before the logic above, and it worked fine.
List<string> regionArray = new List<string>();
if (someCondition)
{
regionArray = _utils.GetRegions(someParam); // this is not returning null
}
foreach (var region in regionArray)
{
var c = region; // this works
}
foreach (var region in regionArray)
{
// region throws null reference exception
var query = from dataSet in myDataSets
where dataSet.Location == region
select dataSet;
var queryResult = query.FirstOrDefault();
if (queryResult == null)
{
// do stuff
} else if (queryResult.State != States.Provisioned)
{
// do stuff
}
}
so most likely, it is not a problem with the moq object. based on #Iliar's suggestion, I will see if regionArray gets modified, but at first glance since regionArray is not used within the loop, my answer would be "no".
Update: I got around this issue by renaming the region looping variable to a different name. As it turns out, I was doing another foreach (var region ...) loop earlier in my code. I spoke to some senior colleagues as to why these 2 names would conflict with each other, and they said maybe it was some issue with symbols in VSCode and not really with my actual code. Thank you all for your help!
There was a lot of info in this thread, so just to summarize here are a few bulletpoints in case it is helpful to someone else in the future:
When debugging an XUnit test, I was seeing my looping variable in my foreach displaying the following info in the tooltip 'region' threw an exception of type 'System.NullReferenceException' Data [IDictionary]:{System.Collections.ListDictionaryInternal} HResult [int]:-2147467261 HelpLink [string]:null InnerException [Exception]:null Message [string]:"Object reference not set to an instance of an object." Source [string]:"9dd66c33104045bba27ad3fc9fb95185" StackTrace [string]:" at <>x.<>m0(<IngestEvents>d__13 <>4__this)" TargetSite [MethodBase]:{System.String <>m0(<IngestEvents>d__13)} Static members ....
even as I stepped INTO the loop, the tooltip for region was still showing the above, and when I typed region into the console, I got 'region' threw an exception of type 'System.NullReferenceException'.
The above 2 points led me to believe region was null. However, through #IVSoftware 's help, I verified that region was not actually null, because the assertion was passing.
I then looked at the rest of my code, and as a random guess, I tried renaming the looping variable region to something else. When I did, region was correctly set to the elements of the list.
Hi I really hope to be helpful. First I will answer your question "how is this possible?" and I think I can explain why your edited question with the inline list works. True, the GetRegions method returns a list that is not null. Sure, if you call GetType() on this it correctly identifies it as a "list of strings". I believe however, that the GetRegions method is returning a list that contains at least one null value. And you prove it out yourself when you added the edit, because you say this works:
regionArray = new List<string>() {"china", "america"};
But try making a list with three values like this where one of them is null and probably the loop will fail again.
regionArray = new List<string>() {"china", null, "america"};
This suggests a bug inside the GetRegions method is putting a null value into the list that it is returning. Adding these two lines at the beginning of your loop might go a long way to identifying the issue:
foreach (var region in regionArray)
{
// Look for this in the Visual Studio 'Output' window
System.Diagnostics.Debug.WriteLine(region == null ? "Null" : region);
// You believe that region is not null. So 'assert' that
// this evaluates to True and if it doesn't the debugger will break here.
System.Diagnostics.Debug.Assert(region != null, "Break on this line if region is null");
...
From what I can tell, I would look inside your GetRegions(someParam) method and see if it's inserting a null into the list somewhere. Good luck!
List<string> regionArray = new List<string>();
if (someCondition)
{
regionArray = _utils.GetRegions(someParam); // this is not returning null
}
this will override the regionArray instance, to the GetRegions instance, so creating new List<string> instance is useless.
What you want is :
List<string> regionArray = new List<string>();
if (someCondition)
{
regionArray.AddRange(_utils.GetRegions(someParam));
}
which is using this new instance, and add the resulted elements inside it.
If _utils.GetRegions(someParam) returns empty set, then regionArray will not be null, but it'll be empty regionArray.Count == 0.
this is also can be done using ToList as well:
var regionArray = _utils.GetRegions(someParam).ToList();
now , you need to check regionArray after that :
if(regionArray.Count == 0)
{
// do something
}
Or using Linq
if(!regionArray.Any())
{
// do something
}
if the collection is not empty then you can iterate through the list and validate each string inside this list before you process it:
foreach (var region in regionArray)
{
// check if the element is null or empty
// if true, will skip this element and go to the next one
if(string.IsNullOrEmpty(region)) { continue; } // go to the next iteration
// get the results
var queryResult = myDataSets.FirstOrDefault(x=> x.Location == region);
if (queryResult == null)
{
// do stuff
}
else if (queryResult.State != States.Provisioned)
{
// do stuff
}
}
I have an object where a property may exist or may not exist.
if(response.AddressInformation.AddressResponses.Any(inf => inf.AddressResponse.matchCodeStatus.ToLower().Equals("usps_match")))
{
}
I have two array items of AddressResponse. First item has null for matchCodeStatus and thats where I get object not set to an instance exception. How can I achieve my target and escape this exception?
I tried to put a null check before my IF, but it didnt work
if(response.AddressInformation.AddressResponses.Any(inf => inf.AddressResponse.matchCodeStatus != null)
As of C# 6, you can also use a null conditional operator ?. :
inf => inf.AddressResponse.matchCodeStatus?.ToLower().Equals("usps_match"))
This question already has answers here:
What is a NullReferenceException, and how do I fix it?
(27 answers)
Closed 5 years ago.
I am trying to get a list item that contains a certain string and I am using this code:
string myListLine= myList.FirstOrDefault(stringToCheck => stringToCheck.Contains("mystring "));
All works well but if the list does not contain a particular string it throws an error:
object reference not set to an instance of an object
I think that I should somehow validate if the string first exists but not sure what would be the best approach.
if the list does not contain a particular string it throws an error:
That is not correct. The exception is thrown, because you have a null value inside your list! If all of your items in the list are valid strings then there will be no exception thrown. In this case FirstOrDefault will simply return null.
I think that I should somehow validate if the string first exists
You can check whether it is null the oldscool way first and combine it with an logical AND && with the Contains method
string myListLine= myList.FirstOrDefault(stringToCheck =>
stringToCheck != null && stringToCheck.Contains("mystring "));
This way the second Contains will not be evaluated if the first condition evaluates to FALSE
You can use the safe navigation operator and the null-coalescing operator to fix this:
System.Collections.Generic.List<string> myList = new System.Collections.Generic.List<string> { null, "Test123" };
string myListLine = myList.FirstOrDefault(stringToCheck => stringToCheck?.Contains("mystring ") ?? false);
The problem occurs if you're calling a method on a null list entry.
Note: If the list is empty FirstOrDefault returns null.
Hope that helps.
Your code simply goes through myList, for each item, it checks if it contains "mystring ".
Only reason you may get a null reference while running that line is your list myList is null. It wouldn't get any error if it is empty.
if you get a null reference after that line, that would mean that myListLine is null, which would mean myList did not contain any items that matched "mystring ".
To make sure you do not get a null reference error with myListLine you should check if it is null before accessing it by using something like this;
if( myListLine != null ){
<Do something to myListLine>
} else {
<list doesnt contain the correct string, alert user.>
}
I think this sample code of mine is one of the safest way by accessing the myList object. If it is null then return an indicator that value was not found or empty.
List<string> myList = new List<string>()
{
"name","adress","phoneNumber"
};
myList.RemoveAll(item => item == null);
string myListLine = myList.FirstOrDefault(stringToCheck => stringToCheck.Contains("myString")) ?? "Not found/Empty";
A variation:
var myList = new List<string>(){"foo","Bar", null,"the mystring"};
string myListLine = myList.FirstOrDefault(s => s == null? false : s.Contains("mystring"));
Same notes as already mentioned regarding FirstOrDefault being null if empty list or no match (does not Contains)
public int getPartijId(string naam)
{
Partij partij = null;
try
{
partij = repository.Partij.Single<Partij>(p => p.naam.Equals(naam));
}
catch (InvalidOperationException)
{
}
return partij.partijID;
}
I want to get a certain value (CD&V) out of our database, by comparing the name in the database with a linq statement but I'm getting a null value back...
With the rest of the values, this method works, but I suspect the problem is '&' in the name/string
Maybe try if your repository of Partij are all partijen
partij = repository.Partij.First(p => p.naam.Equals(naam));
As far as I can tell, the only way your code can return null is if the partijID on the matched object is null.
Other options are throwing a null reference exception
Partij partij = null;
try
{
// this may throw an exception because there may be more or less than one item matching your predicate
partij = repository.Partij.Single<Partij>(p => p.naam.Equals(naam));
}
catch (InvalidOperationException)
{
// this is hiding that exception
}
// this will throw another null reference exception because the first call didn't actually set the partij variable
return partij.partijID;
P.S. It's almost never a good idea to catch an exception then completely ignore it.
How is your table designed? Does the naam field have a unique constraint on it? Are you 100% sure you have exactly one row with a value of "CD&V" in the naam field? My guess would be you're getting multiple rows back and then swallow the exception, so partij stays null.
What's the exception message exactly?
Is partijID actually null in the database?
Goodday
I can't seem to use my dataset in a Null comparison
I'm trying to make an statement (attempts go below) where it will only continue my code when my dataset is empty.
Code 1:
if ((string)dts.Tables[0].Rows[0]["RECID"] != null)
^ just skips my if, I know that it's empty (checked my watch), still continues even when it is null.
Code 2:
long Recid = 0;
Boolean checkrecid = long.TryParse((string)dts.Tables[0].Rows[0]["RECID"], out Recid);
if (checkrecid == false)
^ Crashes at my Tryparse. I know you can use Trycatching, but I don't want to use it, cause it will make my program run slower, and it needs to read a good 10000 lines a day ...
Error:
A first chance exception of type 'System.IndexOutOfRangeException' occurred in System.Data.dll
Meaning that it can't find anything, but I know that already.
EDIT: I do not want an error. Any previous methods, who all work in other cases, return an indexoutofrange error. I'll add this ..
The dataset is filled with data from an SQL server based on phonenumbers and other data.
If he can't find the phonenumber, which comes from a text file, he will return nothing, no row, no column, nothing.
Thanks in advance,
DZ
You need to use DBNull.Value instead of null
EDIT: Index outside the bounds may mean there are no rows at all. Try replacing your if with this:
if (dts.Tables[0].Rows.Count > 0 && dts.Tables[0].Rows[0]["RECID"] != DBNull.Value)
{
}
This line:
if ((string)dts.Tables[0].Rows[0]["RECID"] != null)
needs to be
if ((string)dts.Tables[0].Rows[0]["RECID"] != DBNull.Value)
Or you could delete that check:
Boolean checkrecid = long.TryParse((dts.Tables[0].Rows[0]["RECID"] ?? string.Empty), out Recid);
if((string)dts.Tables[0].Rows[0]["RECID"] is DBNull)
{ // will go here }
Found it!
int strTables = dts.Tables[0].Rows.Count;
if (strTables == 1){ //code goes here}
A type-safe alternative is using Field extension method. It will return 'null' instead of DBNull.Value for empty fields.
if (dts.Tables[0].Rows[0].Field<string>("RECID") != null)