Code contracts in VB.Net Constructors

Question

I'm trying to write a contract for a constructor in VB.NET but it fails to cmpile with

Erreur 17 Malformed contract.: In method MyClass.#ctor(System.Runtime.Serialization.SerializationInfo,System.Runtime.Serialization.StreamingContext), assembly [...]

The method body is

		Protected Sub New(info As SerializationInfo, context As StreamingContext)
			MyBase.New(info, context)
			Contracts.Contract.Ensures(MediaType IsNot Nothing)
			Contracts.Contract.Ensures(MissingProperties IsNot Nothing)
			Contracts.Contract.Ensures(MissingProperties.Count > 0)
 
			_MediaType = info.GetValue("MediaType", GetType(PhysicalObjects.MediaType))
			_MissingProperties = info.GetValue("MissingProperties", GetType(ICollection(Of String)))
		End Sub

Where MediaType and MissingProperties are to member properties. I suppose the problem has something to do with the fact that contracts are not the first instruction but MyBase.New needs also to be the first instruction. Then, anyone has a solution?

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BKQc

Answer 1

I'm afraid I was not able to reproduce the problem. Can you please post a complete example? For instance, this is the example I tried and it seemed to work just fine.

Imports System.Diagnostics.Contracts
 
  Public Class B
    Inherits System.Object
    Public Sub New(a as Integer)
    End Sub
  End Class
 
  Public Class C
    Inherits B
 
    Protected Sub New(x as Integer)
	  MyBase.New(x)
	  Contract.Requires(0 < x)
	  Contract.Ensures(Name IsNot Nothing)
    End Sub
	
    Public Property Name As String
  End Class

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Mike Barnett

Answer 2

Does the class have or inherit any events / members with withevents? Code contracts has a history of not getting along well with VB events and I do remember seeing 'malformed contract' in this sort of situation...

Answer 3

This is still happening in the latest version of Code Contracts (1.4.60317.12) as detailed here: http://stackoverflow.com/questions/15817701/contract-requires-in-exception-ctor-fails-with-error-cc1027-malformed-contract

I have also been able to recreate the issue using version 1.4.50327.0 in VS2010 using the following code:

Imports System.Diagnostics.Contracts

Public NotInheritable Class ValidationException
    Inherits Exception

    Public Property Result() As Object

    Public Sub New(ByVal ValidateResult As Object)
        Contract.Requires(Of ArgumentNullException)(ValidateResult IsNot Nothing, "ValidateResult is nothing.")


        Me.Result = ValidateResult
    End Sub
End Class

Answer 4

Thanks, I can repro it.

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Cheers, -MaF (Manuel Fahndrich)

Answer 5

I fixed this internally now.

The cause for this is some VB compiler inserted code that keeps track of objects passed to constructors. You might want to check out this and related blogs on the subject.

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Cheers, -MaF (Manuel Fahndrich)

Answer 6

Thanks for the fast resposne.

I'm hoping that the fix isn't included in the version that's just been released (1.5.60409.11) as I've just upgraded and am still getting the error.

MM

Answer 7

No, the fix has not been released yet. So what you are seeing is consistent.

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Cheers, -MaF (Manuel Fahndrich)