Inherit From A Generic Class Without Specifying A Type?
Apr 29, 2009
I have the following sample code in a VB.NET console application. It compiles and works, but feels like a hack. Is there a way to define EmptyChild so that it inherits from Intermediate(Of T As Class) without using the dummy EmptyClass?
Module Module1
Sub Main()
Dim Child1 = New RealChild()[code].....
The other way to do this would be to move the generic code out of the Base class and then create 2 Intermediate classes like this [code]...
Then RealChild would inherit from the generic Intermediate and EmptyChild would inherit from the non-generic Intermediate. My problem with that solution is that the Base class is in a separate assembly and I need to keep the code that handles the generic type in that assembly. And there is functionality in the Intermediate class that does not belong in the assembly with the Base class.
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Jan 21, 2010
I can do this without problem.
Class A
End Class
Class B : Inherit A
End Class
Dim Obj1 As A = New B
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Jan 15, 2010
i was trying to inherit System.Type. this is what i have:
[Code]...
and anyway the real problem is that inheriting System.Type without declaring my derived class as 'MustInherit
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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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Aug 14, 2010
I have a Journal that records entries for different types: Journal(Of ParentT)
[Code]....
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Mar 30, 2010
1) VB Allows non-type template parameters2) VB supports explicit specialization 3) VB allows the type parameters to be used as the base class for the generic type4) VB allows a generic type parameter itself to to be a generic 5) VB enforces that all codes are valid for all types of parametrs
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Mar 23, 2011
I'm a newbie to VB, and I am having difficulty understanding what the following (legacy code) class declaration actually means:
Public MustInherit Class ModelBase(Of T As {ModelBase(Of T, TIdType), New}, TIdType)
There is also a related ModelBaseCollection:
Public MustInherit Class ModelBaseCollection(Of TCollection As {ModelBaseCollection(Of TCollection, TModel, TIdType), New}, TModel As {ModelBase(Of TModel, TIdType), New}, TIdType)
Inherits Collection(Of TModel)
I have difficulty understanding the need for the ModelBaseCollection class as the ModelBase class is a generic type.
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Nov 4, 2011
I have a bunch of classes that all contain a Shared ReadOnly Dictionary. If I want to access that Dictionary when the class is a generic type (such as when I have a wrapper function that takes T as an interface that all of these classes implement), what's the way to do it?
I want to do something like GetType(T).GetMember("Dict"), but that will return a MemberInfo type, and that cannot be cast to a Dictionary of my defined type(s). For calling functions this way, one can use a delegate + CreateDelegate + GetMethod. But there doesn't seem to be an equivalent Create*for GetMember stuff. Or am I missing something?
If I plug the GetMember call into the immediate window, and then use a subscript as if it is an array, then the debug output says I am getting a Dictionary back. But if I use that same approach in the actual function that I am trying to write, then I get an error about System.Reflection.MemberInfo cannot be converted to Dictionary(X, Y)
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Apr 18, 2011
Suppose I want to write a generic function that will return the fully qualified name of the data type. In other words, how would you implement the following: Public Shared Function Foo(Of T)() As String ' Return the fully qualified name of T End Function
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Jun 2, 2010
I'm tyring to pass a variable data type to a template class. Something like this:
frmExample = New LookupForm(Of Models.MyClass) 'Works fine
Dim SelectedType As Type = InstanceOfMyClass.GetType() 'Works fine
frmExample = New LookupForm(Of SelectedType) 'Ba-bow!
frmExample = New LookupForm(Of InstanceOfMyClass.GetType()) 'Ba-bow!
[Code].....
I'm assuming it's something to do with the template being processed at compile time but even if I'm off the mark there, it wouldn't solve my problem anyway. I can't find any relevant information on using Reflection to instance template classes either.
(How) can I create an instance of a dynamically typed repository at runtime?
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Mar 1, 2012
I'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].....
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Apr 8, 2010
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]....
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Dec 29, 2010
This is another one of my "I think it's not possible but I need confirmation" questions.I have a base class for a bunch of child classes. Right now, this base class has a few common properties the children use, like Name. The base is an abstract class (MustInherit)Technically, this means that everytime a child class is instantiated, it lugs around, in memory, its own copy of Name. The thing is, Name is going to be a fixed value for all instances of a given child. I.e., Child1.Name will return "child_object1", and Child2.Name will return "child_object2".
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Mar 23, 2011
Public Class notifierMain
Public Class Contacts
Inherits List(Of row)
Public Sub New()
[code]....
When I debug this winforms application I get curType = "notifier.notifierMain+Contacts+row" I want to the Validate function to know it is in MyContacts. How do I do this?
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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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Jun 18, 2009
class inherit from another class and implement an interface?
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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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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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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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Sep 22, 2010
How to simplify this, 2 method in class are identical.First class.
Public Class Gui
Inherits System.Web.UI.Page
Public Sub CreateStyleLink(ByVal StyleArray() As String)
[code].....
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Dec 19, 2010
How to simplify this, 2 method in class are identical.[code]
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Mar 15, 2010
i'm working with different classes and different constructors. It's working fine until i try to inherit a class that also has a constructor. vb asks for mybase.new but when i add that vb says that a constructor cannot call itself, when i try it in a different way vb asks the parameters of the constructor of the class that i want to inherit.
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Aug 25, 2009
By Default code behind looks like --
Partial Public
Class InhAbs
[code].....
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Dec 16, 2009
why is it that Strings are declared notinheritable? plus is there a base class of Integer for us to inherit from?
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Jul 2, 2010
<edit on 7th July, 2010. Please see my 4th post in this threadfor the reason I have marked the post by bpellAS ANSWER </edit>
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May 30, 2011
How to create a class which inherits from a data type, specifically from Char data type? I just want to add one property to it. If it's not possible, are there any other ways to accomplish this?
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Dec 26, 2011
I have problem in Form controls. I inherit label control in a class Mylabel i use this label on my form not standard label control. now i want change the Font all Mylabel in my form then it not change Font when i use standard label control it's work.
I use this code
For Each Ctrl as Control In Me.Controls
Ctrl.font= new Font("Arial",10)
next
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May 5, 2009
I'm compiling a VB.Net 2.0 app (created in VS2008) using msbuild, and now I've added a generic return type, it's giving me the following:
Warning: Type library exporter encountered a generic type instance in a signature. Generic code may not be exported to COM.
Having just spent ages removing all of the previous warnings, I don't really want to add a new one. Any idea how to get rid of it (aside from not using generics)?I don't know what details I'd put in the attribute, or what number to put in the project-level ignore list.
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Sep 12, 2011
I have a question about ASP.Net, visual basic I have 2 LINQ query's, the first one works, the second one doesnt, produces a
"Unable to cast object of type 'System.Data.Objects.ObjectQuery'1[SelmaV2.Products]' to type 'System.Collections.Generic.List'1[System.String]'.
[Code]....
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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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