Weird problem with List(Of T) declaration and .add

I have this really weird problem in my code (.Net Framework 3.5). So, in a normal VB.NET program, I would do something like this :

Dim MyList As New List(Of Integer) 

MyList.Add(3)

MyList.Add(5)

MyList.Add(9)

MyList.Add(17)

And if I put a "break" rigth after

Dim MyList As New List(Of Integer)

and put the mouse over "MyList" while code is paused, I should get : Count=0. However, I have a sub where I create a list just that way and get (when I break after it) : "Count = Property evaluation failed".

It seems like if my list has not enough space to hold the data... Here's the complete code I use to try out everything (by the way, the code itself doesn't really make sense since it's a part of my project). With it I can create the "weird" behavior and anyone can test this. Here's the code (sorry the Code Block button isn't working) :

Structure lPossibilitiesOutputStruct 

     Dim Pinion As GearOutputStruct

     Dim Gear As GearOutputStruct

     Dim Forces As ForcesStruct

     Dim CenterDistance As Double

     Dim Pitch As Double

     Dim lStagePossibilities As List(Of lPossibilitiesOutputStruct)

End Structure

Structure GearOutputStruct

     Dim TeethNbr As Integer

     Dim RPM As Double

     Dim FaceWidth As Double

     Dim OutsideDiameter As Double

     Dim Addendum As Double

     Dim WholeDepth As Double

     Dim OperatingPitchDiameter As Double

     Dim OverPinData As OverPinOutputStruct

     Dim SpanData As SpanOutputStruct

     Dim AllowableBendingPower As Double

     Dim AllowablePittingPower As Double

End Structure

Structure OverPinOutputStruct

     Dim PinDiameter As Double

     Dim OverpinMeasurement As Double

End Structure

Structure SpanOutputStruct

     Dim TeethNbr As Integer

     Dim SpanMeasurement As Double

End Structure

Structure ForcesStruct

     Dim GearSetAxialForce As Double

     Dim GearSetRadialForce As Double

     Dim GearSetTangentialForce As Double

End Structure

Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load

     Dim lStagePossibilities As New List(Of lPossibilitiesOutputStruct)

     Dim MyList As New List(Of Integer)

     MyList.Add(3)

     MyList.开发者_如何学运维Add(5)

     MyList.Add(9)

     MyList.Add(17)

     lStagePossibilities = lGeneratePossibilities(Nothing, Nothing, 3, 1)

End Sub

Private Function lGeneratePossibilities(ByVal ActualStage As lPossibilitiesOutputStruct, ByVal CSL As List(Of Integer), ByVal MaxStage As Integer, ByVal CumulatedRatio As Double) As List(Of lPossibilitiesOutputStruct)

     Return Nothing

End Function

All I did is create a new project with a form and created that code. There's nothing else in the project. I played with the "targeted CPU" and that's all...

If I run that program with compile option to use x86 CPU, and put a break on the "lStagePossibilities = ..." I get the "Count = Property evaluation failed" when i put my mouse over MyList. If I run it with the x64 CPU, then everything is working fine... ("Count = 4"). If I go back with the x86 CPU, I get back the error. Even worst, if I comment the line "Dim Pinion as GearOutputStruct" or the line "Dim Gear as GearOutputStruct" or the line "Dim Forces as ForcesStruct" in the lPossibilitiesOutPutStruct structure declaration, then everything works fine with x86 CPU...

Could it be related to a kind of maximum size of a list ???

Thank you !

Jean

I bet if you changed some of the Strucures into Classes the problem will go away. It is a well known bug in Visual Studio that when Structures get large and try to allocate a lot of local memory things go bad in the debugger. Some of the structures contain other structures and the memory adds up. I bet in x64 the size of the structs gets bigger, due to packing.

To quote some MSDN blogs

Just so others know too. This issue was because of a large struct in my code as well. I converted it to a class and I could read the values of variables hovering over the objects. It worked in some functions and classes, but the error message where the large struct was contained had the error "Cannot evaluate expression because a thread is stopped at a point where garbage collection is impossible, possibly because the code is optimized." and it went away upon making the change. Hope it helps and confirms the solution.

To clarify, what is too big. My Struct has (rather had) ...

• 55 public variables
• A constructor with 6 parameters
• Two public functions (one of those was small and one was large, about 200 lines of code)

I believe structs are intended to be used as small containers of straight forward, simple, cohesive data and functionality, and I would agree that this one got too far out of hand. It started out small, of course, and the needs ballooned. Now that it's in a class where the cohesive data and functionality is now contained there, I can sleep at night. =)

It took me all of 5 minutes to convert it to a class. Easy enough.