.net - Checking For Null Variable In Workflow 4.0 Transition Condition
Feb 27, 2012
I'm implementing a State Machine in WF 4.0. In some transitions, I have added a condition where I check that some variables have the expected values. The variables are enums and booleans, and everything is fine.
However, now I tried to evaluate when a property is null. I have and argument in my workflow, let's say, 'MyArgument'. In a transition, I try to put a condition like 'MyArgument.MyProperty = Nothing'. I never developed in VB.NET, I don't know if I'm missing something here...
VS2010 gives the following error: "Error 4 Compiler error(s) encountered processing expression "MyArg.MyProp = Nothing".
Operator '=' is not defined for types 'XXXX' and 'XXXX'
The type names are exactly the same, and I have debugged VS2010 to ensure that my assembly is not loaded from 2 different locations.
How can I check if the property is null or not?
BTW, I'm using VS2010 SP 1, with .NET Platform Update 1 installed, on W7 64 bits.
Private _PurchaseDelivery as PurchaseDelivery Protected Overrides Sub InsertItem(ByVal index As Integer, ByVal item As PurchaseDeliveryItem)
[Code]....
Which is inside a class which overrides a custom list base. The code is occassionaly throwing an unhandled exception, System.NullReferenceException, on this line when used in production:
If _PurchaseDelivery IsNot Nothing AndAlso _PurchaseDelivery.DefaultSKUBinID.HasValue Then
DeafultSKUBinID is declared as an Integer? (Nullable Int) in the PurchaseDelivery class. I cannot see what might be causing this error, why would this be returning an error?
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currencyPosition = 0 Dim d As Integer = w + 100 For Each currency In Ary
I'm using a loop condition to check if there is null value in the columns, then remove it.
-Original author [STart:] For i As Integer = counter To dt1.Columns.Count - 1 For x As Integer = 0 To dt1.Rows.Count - 1 if some condition then something = true
[Code]...
Sometimes it runs correctly and sometimes even though when i becomes greater than (dt.columns.count - 1), it still executes the for loop and throws an error that there is no column with that index. I must be missing something here but I'm not able to debug the issue.
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If myDevice.dataPacket(1) <> Nothing then myDevice.rxDataReady = False
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If (Len(Form_MainScreen.Ctl48.Value) Or Len(Form_MainScreen.Ctl49.Value) Or _ Len(Form_MainScreen.Ctl50.Value) Or Len(Form_MainScreen.Ctl51.Value) Or _
[code]....
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If Not ds.Tables("tblNotes").Rows(0).IsNull(0) Then ds.Tables("tblNotes").Rows.Clear() End If adp.Fill(ds, "tblNotes")
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Public Shared Function CheckForNull(ByVal obj As Object) As Object If obj <> Nothing Then Return obj Else Return DBNull.Value End Function
I constantly find myself having to do code similar to the following.[code]Is there anyway to check for both on a single line? When i'm checking a condition for a great number of answers, I sometimes end up with conditionals 6-sets deep. If i check for null first, an error still pops up, even though VB shouldn't check since the first condition failed. i.e.[code]
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If DataGridView1.SelectedRows(0).IsDBNull Then MsgBox("Nothing to display") Exit Sub End If
Protected Sub gvwMileStone_RowDataBound(ByVal sender As System.Object, ByVal e As System.Web.UI.WebControls.GridViewRowEventArgs)
[code]...
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For example, getting the lowest date value from an array of dates: Dim dtMostRecent As Date For i As Intger = 0 To myDateArray.Count - 1 If myDateArray(i) < dtMostRecent Then dtMostRecent = myDateArray(i) Next
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Dim myGuid As Nullable(Of Guid) or Dim myGuid As Guid?
It seems doing a myGuid.GetType returns the underlying type, that is type Guid, not Guid?. So testing myGuid.GetType Is GetType(Guid?) always returns False.How do I find out if myGuid is a nullable type?
Ed: I can do the following, which correctly returns True for "Guid?" and False for "Guid":
Not Nullable.GetUnderlyingType(GetType(Guid?)) Is Nothing
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Dim strNames As String strNames = "John Doe, Mark Johnson, Mike Brown, Cindy Smith" If strNames.ToString.Contains("Mike Brown") Then[code]....
How can I assign a variable which may contain a null value to a variable which is declared as Dim var1 as String and then use that variable to insert into access database table?
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