how 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]....
I'm trying to use the type Boolean for some parameter.
<AttributeUsage(AttributeTargets.Method, Inherited:=True, AllowMultiple:=False)>
Public Class MyAttribute
Inherits Attribute
[code].....
I 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?
So 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]...
i am getting all filenames from a directory.parsing out the directory names & the .vb extension then converting those filesnames to classes.Every file in the LPCriteria direcotry is its own class with a "Evaluate" function.[code]
View 1 RepliesI am currently working on a custom data type, and wanted to implement a = operator.
I data type is a nullable date that returns a string value if date was supplied.
I want to allow the variable to be set like this
Dim nd as New NullableDate nd = Today Does anyone know how this can be done, or can anyone point me in the right direction?
I need to create a function which have either 1 parameter with a string as data type or 2 parameters with double as data type.Something like the substring method.
View 2 RepliesI have a TreeView, which contains nodes. When a user clicks on a node, corresponding CrystalReport document should be created and displayed.For example, names of my nodes are: "PeriodReport1", "PeriodReport2", "PeriodReport3". My CrystalReport documents are named same: "PeriodReport1", "PeriodReport2", "PeriodReport3".How can I create and display right type of crystal reports document? I could do something like this:
select case reportName
case "PeriodReport1"
[code].....
I've got this Function:
Public Class QueryStringUtil
Public Shared Function GetQueryStringValue(Of T As Structure)(ByVal queryStringVariable As String) As T
Dim queryStringObject As Nullable(Of T) = Nothing
If queryStringVariable <> Nothing Then
If HttpContext.Current.Request.QueryString(queryStringVariable) IsNot Nothing Then
queryStringObject = CTypeDynamic(Of T)(queryStringVariable)
End If
End If
Return queryStringObject
End Function
End Class
When I try to call it like this:
Dim intTest As Integer = QueryStringUtil.GetQueryStringValue(Of Integer)("stuff")
Dim stringTest As String = QueryStringUtil.GetQueryStringValue(Of String)("stuff")
Dim datetimeTest As DateTime = QueryStringUtil.GetQueryStringValue(Of DateTime)("stuff")
stringTest gives me the error:
'String' does not satisfy the 'Structure' constraint for type parameter 'T'.
I want our other developers to not worry about having to convert a class to a structure or some stuff like that when they call this function. I just want them to be able to put a standard type in the (Of T) and have it work. I don't mind writing in extra calculations to achieve that. The other problem is I also need the function to be able to return an actual null value, so I kind of need the queryStringObject as Nullable(Of T). Which means I have to have T as Structure otherwise it tells me that won't work. So looks like if I change what T is I need to run some calculation to delcare the var as nullable or not.
I tried overloading this method so that one returns T and one returns Nullable(Of T) like so:
Public Shared Function GetQueryStringValue(Of T As Class)(ByVal queryStringVariable As String) As T
Public Shared Function GetQueryStringValue(Of T As Structure)(ByVal queryStringVariable As String) As Nullable(Of T)
And naturally it's telling me it can't do that since they just differ by return types. Is there anyway to overload this? I really don't want to have two functions.
I 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].....
When 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].....
I have a Search Form that can search by a few different fields. The problem field is birthDate. On the form it is a string. In the SQL 2005 db it is a DateTime that can be null.
The code below is sequential as far as declaring the variable on the form and then setting it. Then the call to the BLL and then the call to the DAL.
On this line -->
dgvSearchResults.DataSource =ConnectBLL.BLL.Person.Search(_firstName,_middleName,_lastName,_sSN, (DateTime)_birthDate,_applicationID,_applicationPersonID,_fuzzy);
[Code]....
I 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.
I tried the following, but i get the error
constant expression is required
Public Sub ExampleSub(ByVal Test as string,
Optional ByVal fromDate As System.Nullable(Of DateTime) = Date.Today)
'A Great sub!
[Code].....
How can I create a nullable numeric optional parameter in VB.NET?
View 3 RepliesI want to have a "template" function that can receive different parameter and a type parameter, like:[code]But Vb told me that tupeList is not defined... is there a way I can do that?
View 2 RepliesI've spent quite a bit of time reading up on generics, covariance, etc., and I am failing to understand why I get the aforementioned compiler error in this type of codeLet's say I have a base "Bill" class made up of a collection of Lines..
Public Class Bill(Of L As Line)
Private _lines As List(Of L)
Public Property Lines() As List(Of L)
[code].....
I have the below lines of code :I am getting the error as mentioned in the Title above.This error has come after converting a C# Code to VB.NET Code which is mentioned below:
C#:
public override IChannelListener<TChannel> BuildChannelListener<TChannel>(BindingContext context)
{
if (context == null)
[code]....
I'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)?
I 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?
In 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?
I have the following VB.NET function, for example:Public Function MyFunction (Of TData) (ByVal InParam As Integer) As TDataEnd Sub
View 5 RepliesI 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].....
The 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].....
Why 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)
View 11 RepliesWhen 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 RepliesI'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.
I have a storedproc accepts parameters in XMLtype as
CREATE OR REPLACE PROCEDURE GetDetails(
p_para IN XMLTYPE,
[code].....
Is there a way you can do this ? I would like to have a collection class of T that would be able to do addition, substraction on the T type. I would like to keep T generic instead of having couple collections with the same code, but different types. How would you constrain the generic T?
Example: I would like to define a Collection(of T as IDoMaths). I wouldn't like to create my own integer etc classes with named methods to do the operations, because I think it would be slower. This part of the code is actually called very often and tends to be the bottleneck in performance.
I wonder if this is not possible dim mystring as string="1" dim myint As Nullable(Of Integer) myint=0 myint=mystring It crashes on the last line why is that? mystring is already integer (1) , i dont have to cast using cint, i thought. option strict off- if this cause the problem
View 7 Replies