Setting Nullable Type With IF Operator Failing?
May 27, 2009Why does this give variable A the value of zero (instead of setting it to nothing)?Dim A as double? A=If(2<3, Nothing, 6)
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Assigning Result Of If Operator To System.Nullable Type
Aug 30, 2011When using the If operator [URL] to assign a value to a System.Nullable object, if the result is Nothing (null), then 0 is assigned to the object. Example: 'Expected value is null (Nothing). Actual value assigned is 0. Dim x As System.Nullable(Of Integer) = If(1 = 0, 1, Nothing) If x is a nullable type, why is it being assigned the default integer type of 0. Shouldn't it receive a value of null?
View 2 RepliesNullable DateTime And Ternary Operator?
Nov 15, 2010I'm having problems with a Nullable DateTime in VB.NET (VS 2010).
Method 1
If String.IsNullOrEmpty(LastCalibrationDateTextBox.Text) Then
gauge.LastCalibrationDate = Nothing
[code].....
Assign A Value To A Nullable Integer Via A Ternary Operator?
Aug 24, 2011dim val1 As Integer? = If(5 > 2, Nothing, 43)' val1 = 0 dim val1 As Integer? = If(5 > 2, Nothing, Nothing)' val1 = Nothing What gives? Is this a bug, or am I overlooking something?
View 1 RepliesWhy Does The Ternary Operator Accept A Nullable Boolean
Oct 6, 2011The following compiles in VB.NET (with Option Strict On) and outputs False:[code]Why does that work?The documentation clearly states that the three-argument version of If requires a Boolean as the first parameter:[code]So, why does this work? Is it a bug (or "hidden feature") in the compiler or is it a bug in the documentation and Boolean? is actually a valid type for the first argument of If(a, b, c)?In C#, b ? x : y does not compile if b is of type bool?.I've reported this issue to Microsoft Connect. Someone from MS has replied and confirmed that the documentation will be updated to include the Boolean? case.
View 4 RepliesAssign A Value To Nullable Integer Via A Ternary Operator / It Can't Become Null
Apr 19, 2012If you assign a value to a nullable integer via a ternary operator, it can't become null..While this question may seem like a duplicate of many, it is actually being asked for a specific reason.Take this code, for example: Dim n As Integer? = If(True, Nothing, 1) In that code, the ternary expression should be returning Nothing, but it's setting n to 0. If this were C#, I could say default(int?) and it would work perfectly. Now it looks like I am going to have to ditch the ternary and use a regular If block, but I really want to use the ternary. If Nothing were truly VB.NET's equivalent to C#'s default, how can you explain this behavior?
View 1 RepliesRe-write Conditional Logic That Involves Checking Three Nullable(Of T) Values In An Equality Operator Overload?
Jan 28, 2011So I'm writing the equality operator overload (Operator =())for a custom object, and the resulting mess of If conditionals is just an eyesore. But so far, it seems like the only sane way to check the values to as to match the specific behavior of this object.
The rules are:Num1 is required, period, and both the left and right operands and must be equal for True. Else, False.Num2 is optional, but if specified, must be present for both the left and right operands, and must be equal for True. Else, False.Num3 is optional, but can only be specified if Num2 is also present. Else, False.Num3, if specified, must be present for both the left and right operands, and must be equal for True. Else, False.
[Code]..
I also know that I could cache elements of the checks into booleans and then use those to reduce the amount of text. But that seems like a waste of cycles just for code readability. So I wanted to know if the SO community had better thoughts on reorganizing it, just in case I'm being too verbose with my checks.
The Null Value Cannot Be Assigned To A Member With Type System.Decimal Which Is A Non-nullable Value Type?
Sep 15, 2010I have a Job Register Table and that table doesn't have any records.
This is my LINQ code:
Dim QRecordCount = (From LC In CntxtJobDetails.JobRegistrations _
Where LC.JobCode <> 0 _
[code].....
The Null Value Cannot Be Assigned To A Member With Type System.Int32 Which Is A Non-nullable Value Type?
Aug 18, 2010When i execute this linq to sql command its given an error "The null value cannot be assigned to a member with type System.Int32 which is a non-nullable value type." 0 Records in my Commotidy Table
I want generate manual number and get the last CommodityCode.My Code as follow,
Dim QRecordCount = From RC In cntxtCommodity.CommodityMasters _
Where RC.CommodityCode <> 0 _
Select RC.CommodityCode[code].....
Cast Value Type To Nullable Enumeration Type In Generic Object If All Types Are Unknown At Write-time?
Dec 14, 2011I have a generic Class I'm using to hold information loaded from a database.I have a method which takes a DataRow as an argument, uses the object's known column name and extracts the data from the DataRow, such that:Dim loadData As T = CType(myDataRow("myColumnName"), T))works as my default assignment in most cases.Unfortunately, due to some horrifying design constraints, some of my columns may be null, and may also be taken from enumerations.This means that when <T> is Nullable(Of SomeEnumeration) the above code does not work because I can't cast 0 directly to SomeEnumeration.Zero.Is there some way to check whether <T> is Nullable(Of [Enum])? Or some way to write a method which allows Integers to be cast to Nullable(Of [Enum])?I feel like I'm forgetting something that would allow me to write one of the other of these, but my weak google-fu is turning up nothing.
EDIT: Okay, thanks to dasblinkenlight's answer below, I can detect when this circumstance is occurring, but what I need to do now is to take a type <T> which I know is Nullable(Of SomeClass), get a type reference to SomeClass and then create a new object of type Nullable(Of SomeClass) and assign that to LoadData.My problem was that I had a lot of difficulty in finding any function which would accept baseType as an actual Type.Parse accepted baseType as a parameter, I knew baseType was an [Enum] type because of dasblinkenlight's code, so I was, in this instance, able to code a solution. It's a solution which is very specific to my problem (i.e., T is Nullable(of SomeEnumeration)), but it's a solution nonetheless.
Error: Option Strict On Disallows Operands Of Type Object For Operator '='. Use The 'Is' Operator To Test For Object Identity
Jan 27, 2010I am tightening up my coding with the Option Strict set to ON. It has now produced alot of errors. An example of this is:
If AllocatedDGV.Rows(i).Cells("RoomNumber").Value = RoomsAvailableDGV.Rows(j).Cells("RoomName").Value Then
It gives me the following error: Option Strict On disallows operands of type Object for operator '='. Use the 'Is' operator to test for object identity.
Option Strict On Disallows Operands Of Type Object For Operator Use The 'Is' Operator To Test For Object Identity
Apr 6, 2012I need to write an interface to get data to/from our data files.
We have a low level class that holds field values for each record read from the files.
This just holds two values, the value read from the file (DBValue) and the updated value that may need to be written back to the file (CurrentValue).
These values may be any of the standard value types (integer, date etc) or a string.
Either value (DBValue or CurrentValue) may be null if not defined.
I have written the class to manage this data which works fine while option strict is NOT on.
But we have an office policy of having option strict on all the time.
When I put option strict on, my object value comparisons fail with the error: "Option Strict On disallows operands of type Object for operator '='. Use the 'Is' operator to test for object identity."
Question, how should I change the following code to handle option strict on ...
This is all running on Visual Studio 2010
[Code]...
Setting Nullable Integer To String Containing Nothing Yields 0
Dec 14, 2010I've been pulling my hair out over some unexpected behavior from nullable integers.If I set an Integer to Nothing, it becomes Nothing as expected. If I set an Integer? to a String that is Nothing, it becomes 0! Of course I get this whether I explicitly cast the String to Integer? or not.[code] Previously I had my code up here so without the explicit conversion to Integer? and everyone seemed to be fixated on/confused by that. There were a lot of suggestions that Option Strict On would catch this type of thing. However, this is actually a quirk of the string-to-integer conversion rules which predate nullable types, but still impact them.
View 2 RepliesError: Operator '=' Is Not Defined For Type 'FileInfo' And Type 'Boolean'
Aug 19, 2010This is my
[Code]...
This is my error: Operator '=' is not defined for type 'FileInfo' and type 'Boolean'.
VS 2005 - Operator 'And' Is Not Defined For Type 'Color' And Type 'Integer'
Jun 10, 2009Public Pixels(0 To 95, 0 To 127) As Variant Red = Pixels(X, Y) And &HFF i get this code from VB6, and when i transfer to VB05 i got problem said " Operator 'And' is not defined for type 'Color' and type 'Integer'. " i sent to VS2005
Public Pixels(0 To 95, 0 To 127) As Object
Dim red As Object
Red = Pixels(X, Y) And &HFF
.net - Call To Ctype Failing At Runtime For Cast From Int To Generic Type?
Feb 25, 2011I know about the existence of System.Nullable(Of T) Structure.I am trying to write a class to replace it: The Nullable(Of T) Class [VB code below]. But when I tested the Nullable(Of T) Class (See NullableOfTClassTest Class, Method Main) an exception occurs when using the CType operator to convert from System.Int32.Why does this happen at runtime, why isn't my Ctype operator method being called?
NOTE: code below reordered and reduced in order to hilite problem.
Namespace MyNamespace
Public NotInheritable Class NullableOfTClassTest
Private Sub New()
End Sub
[Code]...
Operator '=' Is Not Defined For Type 'Char' And Type 'Boolean'
Apr 16, 2009In my application when i click the button i'm getting this" Operator '=' is not defined for type 'Char' and type 'Boolean'." But when i test it locally there is no problem at all!
View 2 RepliesCompare Two Variables Of Type Nullable?
Jun 9, 2011I'm trying to compare two variables of type nullable(of boolean) in VB.NET 2010. One of the variables has a value False and the other is Nothing. Now I was expecting the following expression to evaluate to true, but this is not the case:
Dim var1 as nullable(of boolean) = False
Dim var2 as nullable(of boolean)
var2 = Nothing
[Code].....
Why don't I see my MsgBox? How should I compare two nullables (of boolean)?
Nullable(Of ) : Type Of Parameter For <Attribute>?
Mar 23, 2011I'm trying to use the type Boolean for some parameter.
<AttributeUsage(AttributeTargets.Method, Inherited:=True, AllowMultiple:=False)>
Public Class MyAttribute
Inherits Attribute
[code].....
Populating A Nullable Type From A DataRow?
Nov 11, 2010I want to get a value from an item in a DataRow and I would like to store the result in a Nullable Date field.
I see (in VB) that there appears shared "Field" function on the object System.Data.DataRowExtensions. Here's from the Object Browser:
Public Shared Function Field(Of T)(ByVal row As System.Data.DataRow, ByVal column As System.Data.DataColumn, ByVal version As System.Data.DataRowVersion) As T
Member of System.Data.DataRowExtensions
[Code].....
Does somebody have a better way to move values to and from a datarow into Nullable types?
..OR is there a built-in handy function to do this so I don't have to define my own?
.net - Determine If A Generic Parameter Is A Nullable Type?
Mar 3, 2011I have the following VB.NET function, for example:
Public Function MyFunction (Of TData) (ByVal InParam As Integer) As TData
End Sub
How do I, in a function, determine if TData is a NULLable Type?
Cast An Object To A Nullable Of Type Struct?
May 20, 2009In the code base I'm working in there have a method that has the signature
Public Sub SetDropDownValue(Of T As Structure)(ByVal target As ListControl, ByVal value As Nullable(Of T))
The method I am writing is passed a parameter of type object.
How can I cast the object into something that can be passed into the SetDropDownValue method?
Determine If A Generic Param Is A Nullable Type?
Dec 14, 2006I have the following VB.NET function, for example:Public Function MyFunction (Of TData) (ByVal InParam As Integer) As TDataEnd Sub
View 5 RepliesError In Assigning Object Of Nullable Type?
Jul 9, 2010I have a structure that contains another structure. The inner structure is nullable. Now wht I do is something like the following. I create a new instance of the inner structure, set the member variables and assign the whole structure to the inner structure of the parent. But it is giving an error. The assignment is not successful. If I try to peek into the structure in the watch window, it says "property evaluation failed" for the HasValue and Value properties.
Dim testData As List(Of TestData) = Nothing
Dim testData_List1 As New TestData
With testData_List1.commonTestParam
[Code].....
Extension On Nullable(Of T) Object, Gives Type Error?
Oct 29, 2010The code I want to work:
<Extension()>
Public Function NValue(Of T)(ByVal value As Nullable(Of T), ByVal DefaultValue As T) As T
Return If(value.HasValue, value.Value, DefaultValue)
[code].....
Implement Nullable Parameter Of Type String?
Jan 18, 2010how to implement Nullable Parameter of type string in vb.net
Function:
sub savedetail(byval name as string, byval age as integer)
if name isnot nothing then
some work
end if
[code]....
Reflection - .NET: Checking If Variable Is Of Guid (nullable) Type?
Jan 16, 2012I'm trying to check if a variable has been defined as a nullable Guid. eg.
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
The problem is that I don't know how to retrieve the nullable type from the variable itself, in order to test it. I've only been able to get the underlying (non-nullable) system type.
I've written a db helper function. I pass it an object comprised of public members, representing the row data of a table. The members are the table columns.Using reflection, I loop through these public members to create an INSERT statement for a command object and populate its parameters with the values in those members. So far so good.But now there's a table which has a uniqueidentifier column which I must not populate from the row object, as it defaults to "NEWID()" (using SQL Server 2008). Instead of skipping all Guid columns, which would be easy, I only want to skip ones defined in the row data class as "Guid" (non-nullable).Basically, I'm using the Guid? (Nullable) type to indicate it's ok to populate that uniqueidentifier column with data. If it's non-nullable, that tells me to skip it because the column has a NEWID() default value.
C# - Generating Code - Get A Proper String Representation Of Nullable Type?
Mar 17, 2010So I'm building an application that is going to do a ton of code generation with both C# and VB output (depending on project settings). I've got a CodeTemplateEngine, with two derived classes VBTemplateEngine and CSharpTemplateEngine. This question regards creating the property signatures based on columns in a database table. Using the IDataReader's GetSchemaTable method I gather the CLR type of the column, such as "System.Int32", and whether it IsNullable. However, I'd like to keep the code simple, and instead of having a property that looks like:
[Code]...
Unable To Cast Object Of Type X To Type X On Setting DataSource To A Table?
Feb 19, 2012Columns 0 & 1 are filled from a DataAdapter from Access Database and three are added. I had this working, but I changed it to check for the column "Feed" so I could add several Locations. At first this worked,but I did someething in perfecting it and it now fails after filling the first row of the datagridview (dgvFdMed).I ran a check and the table LotsTab has 8 rows filled. Column 1 & 2 are strings and the database appears they are fine. The added columns have just been created with no value. My plan is to enter the values and then use the data from the grid.
Private Sub sfillGrid(ByVal Loc As String)
Dim i As Integer
Dim column As DataGridViewColumn
[code]....
{"Operator '=' Is Not Defined For Type 'DBNull' And Type 'Double'."}?
Jan 12, 2009when a user inputs a value into a text box, i am searching that value in my dataset.although the number that i entered is in my dataset, i am getting this excemption.
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