Myujth

I have a .Net 4.6 web application that has a chronic yet intermittent problem where an error occurs, always at the same spot, which crashes IIS.

The web app is used everyday, but this error doesn't happen everyday. But when it does error out and crash the website, it's always on the same line.

Here's the error:

[NullReferenceException: Object reference not set to an instance of an object.]
SecureUserCheck..ctor(Dataset secureData) in e:gameServerSecureUserCheck.vb:160

Here is how "ds" is initialized:

Dim ds As Data.DataSet = Session("secureData")

 If IsNothing(ds) Then
 ds = getSecureDS(gameID)
 Session("secureData") = ds
 End If

Here is SecureUserCheck.vb with line 160 below:

inhSec = New SecureUserCheck(ds)

 Public Sub New(ByVal secureData As DataSet)

 If secureData Is Nothing Then
 Throw New System.ArgumentException("secureData in empty.")
 Else
 startTime = DateTime.Now
 Try
 myGameInfo = secureData.Tables("GameInfo") // LINE 160
 Catch ex As Exception
 Throw New System.ArgumentException("The secureData must contain [GameInfo] table.")
 End Try
 With myGameInfoRows(0)
 ...fill variables
 End With

I tried wrapping it in a Try Catch block, but that never seems to be thrown. The error will still pop up and crash IIS.

Is there anything I can do to check and make sure the datasets and datatables exist, or not null so that IIS doesn't crash?

Thanks!

First, you should use Option Strict On. It will help you get all the types matching up correctly, which leads to fewer errors and faster code.

Now, onto the main issue. If you can do something useful about a problem encountered while the program is running, you should. In this case, you can re-initialise the data if it has been lost:

Public Sub New()
 Dim ds As Data.DataSet

 If Session("secureData") Is Nothing Then
 ds = getSecureDS(gameID)
 Session("secureData") = ds
 Else
 ds = DirectCast(Session("secureData"), Data.DataSet)
 End If

 If Not ds.Tables.Contains("GameInfo") Then
 Throw New System.ArgumentException("The secureData must contain [GameInfo] table.")
 End If

 ' more code...

End Sub

Please also notice the cleaner way of checking if a particular table exists, although I suggest it properly belongs in the getSecureDS method.

If the dataset applies to all users of the site, you should consider using System.Runtime.Caching instead of session state.