IsNot Nothing Question

[ssabc]

Hello:

I have a string that can occasionally equal nothing, so my solution is to skip it when this is the case.

                        If EdmSearchResult.Path IsNot Nothing Then
                            ReturnFileName = EdmSearchResult.Path
                            Return ReturnFileName

                        End If

The problem is, the code gets stuck on the If statement because the value is nothing.

What about this logic is incorrect?

Thanks!

[kpmc]

Are you initializing it as nothing?

Dim ReturnFileName As String = Nothing

maybe check of empty or null and/or whitespace, etc

When dealing with checking string nothingness I've grown happy with just checking the Length property

If MyString.Length <=0 Then
 'this is obviously nothing
End If

[PlausiblyDamp]

Hello:

I have a string that can occasionally equal nothing, so my solution is to skip it when this is the case.

                        If EdmSearchResult.Path IsNot Nothing Then
                            ReturnFileName = EdmSearchResult.Path
                            Return ReturnFileName

                        End If

The problem is, the code gets stuck on the If statement because the value is nothing.

What about this logic is incorrect?

Thanks!

When you say "code gets stuck" are you getting an error or some other unexpected behaviour? Which value is nothing, EdmSearchResult or EdmSearchResult.Path? Your code is checking EdmSearchResult.Path but this will fail if EdmSearchResult is nothing.

[kebo]

@kpmc
Checking the length on a string that is nothing will fail. Since it is nothing, it's length doesn't exist.

Need to check for nothingness first...

If (MyString IsNot Nothing ANDALSO MyString.Length>0)
'do something
End If

@ssabc
If it EdmSearchResult.Path that is noting or is EdmSearchResult nothing?
Try this.

If EdmSearchResult IsNot Nothing AndAlso EdmSearchResult.Path IsNot Nothing Then
'do something
End If

[kpmc]

Checking the length on a string that is nothing will fail. Since it is nothing, it's length doesn't exist.

For some reason I thought this would return -1 in that event

I guess Ive not run into the Null reference exception bcz I always initialize my string with empty value before using them anywhere.

[ssabc]

This is good. I just removed the Path. The issue is, EdmSearchResult.Path was equal to Nothing!! Thus, EdmSearchResult is also equal to Nothing.

Apparently, this does not play well with strings.

The EdmSearchResult.Path.Length <=0 thing (previous reply) also did not work.

Things are moving along, but if I only had a string to check, what would be the answer? Even initializing as Nothing or "" produced undesirable results.

[kebo]

The issue is, EdmSearchResult.Path was equal to Nothing!! Thus, EdmSearchResult is also equal to Nothing.

The existence of child property of a class has no bearing on whether the class itself exists or not so that statement makes no sense. Maybe you just typed it backwards.

If you want to know if a string (or any other class) exists, you need to test is against Nothing, (i.e MyClass Is/IsNot Nothing). If that is not working you have something else that is wrong.

[dday9]

A String is a reference type and can be equal to Nothing, but more often than not the default value of a String is String.Empty. Could you elaborate on the situation that causes the String to be equal to Nothing to begin with?

[Shaggy Hiker]

Thus, EdmSearchResult is also equal to Nothing.

I'd say that is the answer, though the "Thus" is wrong. EdmSearchResult was nothing, so accessing the Path member caused an exception.

[jmcilhinney]

If what you want to know is that EdmSearchResult is not Nothing and that EdmSearchResult.Path is not Nothing then the most efficient way in VB 2017 is to use null propagation:

If EdmSearchResult?.Path IsNot Nothing Then

The 'EdmSearchResult?.Path' expression will evaluate to Nothing if either EdmSearchResult or EdmSearchResult.Path is Nothing. If you want the String to not be empty too then use this:

If Not String.IsNullOrEmpty(EdmSearchResult?.Path) Then

[i00]

If what you want to know is that EdmSearchResult is not Nothing and that EdmSearchResult.Path is not Nothing then the most efficient way in VB 2017 is to use null propagation:

If EdmSearchResult?.Path IsNot Nothing Then

The 'EdmSearchResult?.Path' expression will evaluate to Nothing if either EdmSearchResult or EdmSearchResult.Path is Nothing. If you want the String to not be empty too then use this:

If Not String.IsNullOrEmpty(EdmSearchResult?.Path) Then

Also for the second eg here you can just use:

If EdmSearchResult?.Path <> "" Then

... string comparisons with = "" is the same as IsNullOrEmpty in VB.Net -- which I really like

Kris