.net - Retrieving Generic Argument Types

Oct 23, 2009

I am using VB.Net. I have an object class called clsA(of T as clsB). Depending on what T is, I want to do different things. Let's say that clsC and clsD both inherit clsB and therefore can be used for T.

If I have an instance of clsA(of clsC), how can I get the inside type (i.e. clsC) using reflection?

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Argument Types Do Not Match QueryExtender

May 3, 2011

I have an Entity I'm pulling three columns from Title (nvarchar(256)), Popularity (int), and Type (int). I'm then trying to use QueryExtender on a radiobuttonlist to allow the end user to filter out all but specific results but I keep getting an "Argument Types do not match" error. Here is the actual code:

<asp:QueryExtender ID="QueryExtender1" runat="server" TargetControlID="EntityDataSource1">
<asp:SearchExpression DataFields="Type" SearchType="StartsWith">
<asp:ControlParameter ControlID="rblTypes" PropertyName="SelectedValue" />
</asp:SearchExpression>
</asp:QueryExtender>
[Code] .....

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.net - Casting Generic Types?

Apr 20, 2010

Public Function CastToT(Of T)(ByVal GenericType(Of Object) data) As GenericType(Of T)Return DirectCast(data, GenericType(Of T))End Function

The above clearly does not work. Is there any way to perform this cast if I know that all objects inside data are in fact of Type T?

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Define A Generic That Can Take Several Possible Value Types?

May 4, 2011

Is there any way to define a Generic in VB.NET which will accept only Singles or Doubles? I tried the following things, based on what I've found online, but none compile:

Dim target As Nullable(Of {Single, Double})
Dim target As Nullable(Of T As {Single, Double})
Dim target As Nullable(Of T {Single, Double})
Dim target As Nullable(Of Single, Double)
Dim target As Nullable(Of T As Single, Double)

I want to specify that target can either be a Single? or a Double? only.

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GetType On Generic Types

Dec 2, 2010

I'm trying register presenters with Windsor using the convention based method but trying to do this in VB.NET, but the problem is it does not want to compile this statement:

Dim type = GetType(AbstractPresenter(Of))

I am getting : Too few type arguments to AbstractPresenter(Of TView, TPresenter)

Which I don't understand because this is a valid statement according to question. Also showing valid in other C# to VB.NET converters when converting typeof(AbstractPresenter<>).

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Specify Generic Types On Delegates?

Nov 15, 2010

Maybe I am just not reading the MSDN documentation correctly, but given a function that takes in one string parameter and returns type T, how can this be specifed as a shared function using Func()?

MSDN says Func(Of In T1, Out TResult), but all of their examples use the same data type, i.e., Func(Of String, String). I want to do Func(Of In String, Out T), where T is arbitrary (but I can constrain it if necessary by a base class). I want it shared/static at the class level, yet the encapsulating class will itself not be a generic class. It seems in this specific scenario, it's impossible to do what I want because the compiler would have no way of knowing what Type T is at runtime.

So is it possible to do generics on delegates or anonymous lambda expressions in VB.net (not C#)?

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Arrays And Generic Types - Conversion

May 10, 2011

Well this is maybe a little different than other array based conversion questions, but I'm dealing with forced typing concerns due to interface implementation and thus would like a few opinions on the process. I've basically redesigned the Collection suite for .Net because I don't like the extreme simplicity of the default Collections and dictionaries, as well, when I want the more complex concepts I don't want to have rewrite the same collection over an over again.

[Code]...

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C# - What Are All Of The Generic Collections/types In The 4.0 .NET Framework

Nov 29, 2010

Is there an exhaustive list of all of the "base" (not used in an object-oriented sense but more in a common sense) generic types in the 4.0 .NET Framework? I have found this list that I often send newer/mid-level devs to so they can understand how non-generic types map to generic types, but this is by no means exhaustive. I'm looking for something that also includes things such as KeyValuePair<>, Tuple<>, and other basic generics that may not be very-well known. Interfaces such as IObservable<> would be nice but not necessarily required.

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Use A Generic That Only Accepts Integer Types?

Mar 5, 2010

Is there a way to use a generic that only accepts integer types?

I have a Clamp(value, min, max) function, and it would be nice if it could accept ints, uints, floats, shorts, ect without having to write an individual function for each type.

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C# ::Generic Overkill To Define Multiple T Types?

May 25, 2011

NOTE: I am mixing VB and C# - snippets come from different librariesI have a VB class definition as follows:

Public Class Session(Of TConnectionBuilder As {DbConnectionStringBuilder, New}, _
TConnection As {DbConnection, New}, _
TDataReader As {DbDataReader})

[code].....

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Use Generic Constraints Based On Attributes Rather Than Types?

Aug 28, 2009

I'm trying to write a class that will be in charge of persisting application options. Since the options need to be persisted the values that I'm sent must be serialisable.

Initially I thought I've be able to write a method with a signature like this[code]...

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Generic BitConverter.GetBytes For Primitive Data Types?

Jan 19, 2012

addressing the need for getting the bytes of an object. But I am wondering if there is an approach to calling BitConverter.GetBytes on a generic type where I know the type is a primitive (Int32, UInt16, etc).

Public Sub Foobar(Of T as Structure)()
Dim x as T 'Assume T is declared as Int32
Dim y() as Byte
y = System.BitConverter.GetBytes(x)
End Sub

The above will throw your usual error:

Overload resolution failed because no accessible 'GetBytes' can be called with these arguments:
'Public Shared Function GetBytes(value As Double) As Byte()': Value of type 'T' cannot be converted to 'Double'.
'Public Shared Function GetBytes(value As Single) As Byte()': Value of type 'T' cannot be converted to 'Single'.

[code]....

One solution I think would work is a large Select Case calling GetType(), but that is horrendously slow (because of boxing) and looks ugly. I would think that since I call my higher level class with a primitive data type for T, that the compiler would be smart enough to figure it out, but I assume I am not providing enough information for it to derive what T's underlying value is at compile time for the invoked instances.

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How To Match Generic Types, Without The Type Parameter In A IF-ELSE Statement

Jan 23, 2009

I have bee trying to figure out, how to match generic types, without the type parameter in a IF-ELSE statement - heres what i mean:

<P>IF TypeOf(Obj) Is GenericTypeExample(Of ???Any???) Then</P>
<P>End if</P>

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Write A Generic Function In .NET That Only Accepts Numerical Types?

Jun 4, 2009

Suppose I want to write a function like the following (as usual, a trivial example for illustrative purposes):

Public Function calcSqSum(Of T)(ByVal list As IEnumerable(Of T)) As T
Dim sumSq As T
For Each item As T In list

[Code]....

As you can probably guess, this function causes an error because a generic object is not guaranteed to implement the + operator. As far as I know, though, any numerical type (Integer, Double, Decimal, etc.) will.

Is there a way to write a (quasi-)generic function that can accept any numerical type, without having to explicitly overload the function for every such type yourself?

Alternatively, I suppose an equally acceptable solution would be to somehow check if a type implements the '+' operator (or any operator generally associated with numerical types and used by the function).

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Retrieving From Database - Error "column Argument Cannot Be Null"

Mar 11, 2010

[Code]...

'column' argument cannot be null. Parameter name: column

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Generic Mustinherit Class - Receive: "Type Argument BaseObject Is Declared 'MustInherit' ?

Aug 23, 2011

i have 2 mustinherit classes where one is a generic one:

'Visual Basic 2008 - .net 3.5 - Any CPU
Public MustInherit Class BaseObject

End Class

Public MustInherit Class BaseObjectList(Of T As {New, BaseObject})
Inherits List(Of T)
End Class[code]...........

i receive: "Type argument BaseObject is declared 'MustInherit' and does not satisfy the 'New' constraint for the type parameter"users would never enter data in the wrong form,files they choose to open would always exist and code would never have bugs.

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Strongly-typed Generic Method Invokes Its Argument's Base Class Method Instead Of A Shadowed Method In T?

Oct 19, 2010

Consider a MyForm class that contains a shadowed implementation of Show(). It also contains a CreateForm() method, which accepts an instance of the form and calls the shadowed sub:

[Code]....

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Cast Value Type To Nullable Enumeration Type In Generic Object If All Types Are Unknown At Write-time?

Dec 14, 2011

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.

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Error - Soap Serializer Does Not Support Serializing Generic Types : System.Nullable`1[System.DateTime]

Oct 2, 2009

Im working on my first n-tier application. I am trying to serialize a structure and Im getting an error"Soap Serializer does not support serializing Generic Types : System.Nullable`1[System.DateTime]."Here is the structure that is being serialized
Namespace Structures

<Serializable()> _
Public Structure structAllergy
Public AllergyID As String
Public ProfileID As String

[code]....

The bold line is the line that is throwing the error.

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Constrain A Generic Method / Extension Method To Numeric TYPEs Only?

Sep 16, 2010

Write an overload for every numeric type or if possible constrain a generic extension method to just numeric types.

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Sql Server - Assign The Value I Queried To A String Which Is An Argument In A Procedure If The Argument's Data Type Is An Object?

Dec 5, 2011

I made this procedure re-use a select query:

[code..]

And I use it like this if I would want the selected value placed in a textbox and it works fine

[code...]

However if I want the value to be passed in a string like so:

[code...]

The string ends up having an empty string value. How do I assign the value I queried to that String?

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Is There A Concept Of "Generic Structure" Similar To Generic Collections, Generic Classes

Dec 16, 2009

We have migrated our Vb6 application to VB.NET using a third party tool. Now we are in a process of Refactoring and introducing object oriented concepts in the application.

In VB6, we were using structures in many places. As a part of introducing object oriented programming,

1. is it a good idea of changing all Structures to Classes? or Is there a concept of "Generic Structure" similar to Generic collections, Generic classes?

2. Can some one guide me any source containing guide lines or best practices for applications that are migrated to VB.NET from VB6 and implementing object oriented programmaing.

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.net - Can A Generic Version Of A Derived Class Override A Base Method Using The Generic Type

Apr 13, 2012

Consider:

Public MustInherit Class Column
Public ReadOnly Property ReturnSomethingUseful() As Object
Get
'return something useful

[code]....

But this gives the following error:

Public Overrides Function ParseValue(sValue As String) As Boolean'
cannot override 'Public Overridable Function ParseValue(sValue As String) As Object'
because they differ by their return types.

I accept that you can't do this, but I'd like to be able to preserve the semantics of what I'm. trying to do, which is to have an untyped version that deals with Object, but a typed version in derived classes that knows about the specific type T.

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C# :: Determining Object Equivalence For Value Types, Reference Types And ILists?

Nov 1, 2009

I have a class with a Property called 'Value' which is of type Object.Value can be of any type, a structure, a class, an array, IList etc.My problem is with the setter and determining whether the value has changed or not.This is simple enough for value types, but reference types and lists present a problem.For a class, would you assume that the Equals method has been implemented correctly, or just assume that the value has changed every time the setter is called?If I did assume it's changed, then perhaps I should assume it for value types as well, so that the behaviour is consistent.

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.net - Determining A Generic Type At Runtime In Non-Generic Class

Aug 14, 2010

I have a Journal that records entries for different types: Journal(Of ParentT)

[Code]....

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Construct A Generic Interface Class With Generic Functions

Nov 25, 2011

I am trying to construct a generic interface class with generic functions. My goal was to use this to implement multiple worker classes for database interaction that have the same basic functionality. Each class will deal with different object for example, category, product or supplier but unless the the functions in the interface are generic that this won't work.This is the interface code that I have but I don't know if I have done it correctly. [code]

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.net - Creating A Generic List Of A Generic Type

Jun 30, 2011

I am trying to create a list of a generic type in vb.net 2.0 framework.
This is the generic type definition:

Public Class GenericParamMap(Of T)
Public Sub New(ByVal pParamName As String, ByVal pPropValue As T)
mParamName = pParamName

[Code]....

The compiler does not allow a "T" in the method's parameter because it's not defined, but I'm not sure how or where to define it. I thought it was okay to have a generic method definition.

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Generic Cannot Instantiate Instance Of The Generic Type With New?

Feb 8, 2012

I am trying to write a generic method, to avoid code duplication, which will create or activate a Form as an MDI children, based on its type. But I have to lines in error (see comments).

[Code]...

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VS 2008 Accessing Something With A Generic Generic?

Jun 19, 2012

If i have an object that implements an interface (and don't know the exact object) i can call a sub (DoSomething) by going:

vb
Dim iObj = trycast(something, iInterface)
if iObj isnot nothing then
iObj.DoSomething()
end if

How can I do this for a Generic? such as...

vb
Public Class TestClass(of T)
Public sub DoSomething()
....
end class

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Compare Two Types In Dictionary Of Types .net?

Jun 23, 2012

I need to compare two dictionary values if the types stored are equal, this is what i have

if gettype(Args(key)) = gettype(argtypes(key)) then
'' do something
end if

[Code]....

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