访问字段值时检查Null值

Question

I am attempting to check a field value for null.

Assuming that item is a valid Outlook ContactItem, the following code, I would have thought, would have checked for a null value and returned "(Empty)" if the relevant field is null.

EntryID = item.EntryID.ToString() ?? "(nothing)";
Title = item.Title.ToString() ?? "(nothing)";
First_Name = item.FirstName.ToString() ?? "(nothing)";
Middle_Name = item.MiddleName.ToString() ?? "(nothing)";
Last_Name = item.LastName.ToString() ?? "(nothing)";
Suffix = item.Suffix.ToString() ?? "(nothing)";
Company = item.CompanyName.ToString() ?? "(nothing)";
Home_Phone = item.HomeTelephoneNumber.ToString() ?? "(nothing)";
Mobile_Phone = item.MobileTelephoneNumber.ToString() ?? "(nothing)";
FirstLastName= item.LastNameAndFirstName.ToString() ?? "(nothing)";

However, what is happening on other fields, is an error as follows:

Object reference not set to an instance of an object. 

The error is not a NullReferenceException in the strict sense - the error relates to the contacts field not the ContactItem object.

Now would I be right in saying that the error is actually telling me that the field is in fact an object, which if it does contain text, is removed from the ContactItem ?

I have attempted to mitigate the error, by filling in each field in an Outlook Contact - the error does not get thrown - but if I delete the field contents, of say CompanyName, the code will fail on that line with the same error.

If I am right, then how would I check if the object exists prior to trying to get the field contents?

MTIA

DWE

Answer 1

Try using the null-conditional operator.

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

Example: If Property is null:

EntryID = item.EntryID?.ToString() ?? "(nothing)";

If item is null:

EntryID = item?.EntryID.ToString() ?? "(nothing)";

Or check both

EntryID = item?.EntryID?.ToString() ?? "(nothing)";

Answer 2

Try Using Ternary Conditional Operator

Condition ? True : False

If you are retriving data from Database then this

if(item.EntryID.ToString() == DBNull) ? item.EntryID.ToString() : "(nothing)";

And if still shows error then try to put ? with datatype of EntryID

public string? EntryID;