ArcObjects conform to .NET standards Error

Question

So, I'm following the "Walkthrough: Migrating VB6 to VB.NET for ArcGIS 10" to convert my VB code to .NET (using Visual Studio 2010), and I'm running into this error, "NullReferenceException was unhandled by user code", object reference not set to an instance of an object. It suggests that I use a "new" keyword to create an object instance. I imported all my namespaces under Option Explicit (for this example the GeoDatabase namespace was imported), and turned Option Strict On, and applied all the CType conversions that VS required. Since this walkthrough example is for ArcGIS 10, and I'm using 9.3.1, could this be the issue? I tried to pass the "new" keyword below, but I'm still getting the error. Here is the code. Any input will be greatly appreciated.

If SelectionSet.Count < 1 Then
        MsgBox("Please select one or more wells", MsgBoxStyle.Critical, "No Selected Wells")
        Exit Sub
        'Retrieve all features
        'Set pFeatCursor = pFClass.Search(QFilt, False)
    Else
        'Retrieve just the selected features
        'This statement moves the selected features into a feature cursor.  All
        'subsequent work is done using the feature cursor.
        'UPGRADE_WARNING: Couldn't resolve default property of object pFeatCursor. Click for more: 'ms-help://MS.VSCC.v90/dv_commoner/local/redirect.htm?keyword="6A50421D-15FE-4896-8A1B-2EC21E9037B2"'
        SelectionSet.Search(QFilt, False, CType(FeatCursor, ICursor))
    End If

    'Get the first feature
    Dim Feature As IFeature = Nothing 
    Feature = FeatCursor.NextFeature '<<<ERROR

Thank You!

Update

So, I have my ICommand Sub that calls my CreateStick Sub with the new ByRef Cursor As ICursor exception.

 Private Sub ICommand_OnClick() Implements ICommand.OnClick
        Me.CreateStick()
    End Sub

 Public Sub CreateStick(ByVal QueryFilter As IQueryFilter, ByVal Recycling As Boolean, _
    ByRef Cursor As ICursor)

I stil have two errors on this line:

SelectionSet.Search(QFilt, False, ByRef CType(FeatCursor, ICursor))

ByRef and ICursor are underlined. ByRef = Expression expected and ICursor error = ICursor is a type and cannot be used as an expression.

Answer 1

ByRef and ICursor are underlined. ByRef = Expression expected and ICursor error = ICursor is a type and cannot be used as an expression.

When you have the keyword ByRef you can ONLY have a variable following it. What you have following it is a function. ByRef means that the variable you are giving to the function you expect to change in the function and you want to preserve that change outside of the function. You cannot do a CType here because that is its own function.

Instead do your cast first and place that new variable after the ByRef.

Good Luck

Answer 2

The ArcObjects API states the following for the Search method you used in your example:

[Visual Basic .NET]
Public Sub Search ( _
    ByVal QueryFilter As IQueryFilter, _
    ByVal Recycling As Boolean, _
    ByRef Cursor As ICursor _
)

Which means that you forgot to supply the needed ByRef keyword for your cursor. Thus it doesn't get assigned and you will get a NullReferenceException when trying to access any method on that empty reference. This should fix your problem:

SelectionSet.Search(QFilt, False, ByRef CType(FeatCursor, ICursor))

EDIT: Edit your code like this:

Dim cursor as ICursor
cursor = FeatCursor
SelectionSet.Search(QFilt, False, ByRef cursor)

PS: Please don't downvote answers which aren't by definition wrong.

Answer 3

I'm not an VB master but will take a poke at this one. At least in the code you've posted, it doesn't like FeatCursor is being initialized, or declared anywhere for that matter.(unless the CType statement does something magical to the variable?). Try 'Dim pFeatCursor as ICursor' before your if/else statement.