ignore null reference exception vb.net - vb.net

Question

I am coding in vb.net.
At times the data is empty/null this is due to user's input into the db.
i will like to bypass it, however i get no luck.
here is snippet of my code:
If hct.mydbvalue.name IsNot Nothing Then
dr("mydbvalue") = hct.mydbvalue.name
End If
I still get an error:
System.NullReferenceException: Object reference not set to an instance of an object.
is there a way if it is a null value to not do anything?

Answer 1

Both #FishBasketGordo and #Yuck are correct, you need to check the full object path for nullability:
If (hct IsNot Nothing) AndAlso (hct.mydbvalue IsNot Nothing) AndAlso (hct.mydbvalue.name IsNot Nothing) Then
dr("mydbvalue") = hct.mydbvalue.name
End If

Answer 2

You won't get a NullReferenceException from data in the database that's null when using ADO.NET; ADO.NET uses DBNull.Value to represent null, so your null reference is coming from somewhere else. In the code above, your exception could occur if any of the following were null:
hct
hct.mydbvalue
dr

Answer 3

Make sure that the whole chain is not null. If hct or mydbvalue is null, you'll get the exception.

Answer 4

To me this looks like hct.mydbvalue is null, and therefore you can't call "name" on it.

Answer 5

Private Function NullCheck(ByVal inObject As Object, Optional ByVal defaultValue As Object = "") As Object
Dim out As Object
If Not IsDBNull(inObject) Then
out = inObject ' This returns the value that was passed in when it is not null
Else
out = defaultValue ' This ensures that out is something and defaults to ""
End If
Return out
End Function

Answer 6

You should be checking whether hct is Nothing, as well as mydbvalue. If you look at the exception message property, it will tell you which is causing the error.

Answer 7

I'm also solving this problem, but in C#.
On my project we've complex object paths like "RootObject.childObject.LitleObject.TinyObject.StringName"
when any of these objects in the path is null, you'll get a null reference when you try something easy like
if(RootObject.childObject.LitleObject.TinyObject.StringName == "a")
I would be okay if it just works as whole rest of the path will be null.
eg. when childObject = null, then I want also RootObject.childObject.LitleObject.TinyObject.StringName to be null, not null reference exception.
However I've found no solution yet, but there is one new operator which can slightly help you in some null tasks.
a = object.object ?? defaultValue;
operator ?? is something like ISNULL in SQL server. If object on left is null, it returns the object from right.
It also replaces whole function NullCheck posted by Michael above.
Hope this will help a bit.
more info on operators
http://msdn.microsoft.com/en-us/library/ms173224(v=vs.80).aspx
http://msdn.microsoft.com/en-us/library/6a71f45d(v=vs.80).aspx

Answer 8

you're talking about diferent things.
It doesn't matter if you use ISDBNull(x.y), String.IsNullOrEmpty(x.y) or (x.y=null)
The problem is far sooner than your selected function is called.
when X is null, it cannot have a property Y. so when you call
AnyOfYourPrefferedFunctions(x.y);
the error raises during evaluation of x.y (null. doesn't exist), so it stops before the machine actually knows what is the function you want to call.
Probably only way to check this, would be using reflection. But you would need to send string with path and reference to root. so something like:
var v = GetValueThroughReflection(rootObject, "rootObject.path.to.the.last.object");
Then you'll be able to write a function which will go through the object path and find which one is null and handle it accordingly. e.g. returns null.
But when you'll heavy use that function, it can make your application run slower. as you'll use reflection for such simple task as is getting value out of variable.

Answer 9

from VS14+ you can use
If hct?.mydbvalue?.name IsNot Nothing Then
dr("mydbvalue") = hct.mydbvalue.name
End If

Answer 10

Try inserting a IF NOT isdbnull(hct.mydbvalue.name)

Answer 11

The following code checks all values.
If hct IsNot Nothing AndAlso
hct.mydbvalue IsNot Nothing AndAlso
Not String.IsNullOrWhitespace(hct.mydbvalue.name) Then
dr("mydbvalue") = hct.mydbvalue.name
End If
Note that the last test used String.IsNullOrWhitespace(). I'm assuming name is a string and you don't want to save empty strings.
Update 1
The following code is a simple console application to prove that using IsDbNull() or Micheal's NullCheck() will throw NullReferenceException when hct.mydbvalue is Nothing.
Module Module1
Sub Main()
Dim hct = New hct
Dim dr = New Dictionary(Of String, String)
Dim errorCount = 0
Try
Dim thisCallWillFail = IsDBNull(hct.mydbvalue.name)
Catch ex As NullReferenceException
Console.WriteLine(
"Using IsDBNull() threw NullReferenceException as expected."
)
errorCount += 1
End Try
Try
Dim thisCallWillFail = NullCheck(hct.mydbvalue.name)
Catch ex As NullReferenceException
Console.WriteLine(
"Using NullCheck() threw NullReferenceException as expected."
)
errorCount += 1
End Try
Console.WriteLine("errorCount = 2? {0}", errorCount = 2)
End Sub
Private Function NullCheck(ByVal inObject As Object,
Optional ByVal defaultValue As Object = "") As Object
Dim out As Object
If Not IsDBNull(inObject) Then
' This returns the value that was passed in when it is not null
out = inObject
Else
' This ensures that out is something and defaults to ""
out = defaultValue
End If
Return out
End Function
End Module
Public Class hct
Property mydbvalue As mydbvalue
End Class
Public Class mydbvalue
Property name As String
End Class