First Parameter In The Definition Of .NET Generics Uses The 'Of' Keywo?
Dec 13, 2011
Why only the first parameter in the definition of VB.NET Generics uses the 'Of' keyword ?
For example I have here the the full code that LINQ uses for the Enumerable.Select() method :
<System.Runtime.CompilerServices.Extension()> _
Public Shared Function [Select](Of TSource, TResult)(
ByVal source As IEnumerable(Of TSource),
ByVal selector As Func(Of TSource, TResult)
) As IEnumerable(Of TResult)
I'm facing really strange problem, in one of my BLL files whenever I add method or property i get this message Error1'CPLogic.BLL.OrdersFaxGroups' does not contain a definition for 'GetFaxGroupForStatusCheck'C:CouponphoneAppsCPFaxEngineCPFaxEngineCPFaxEngineFaxEngine.cs20658CPFaxEngine I know that the method is in that file, i even able to build the application with success but when ever i try to lanuch it i get this message, the same thing happend to me yesterday in the same file, i ended up deleting it and copy its content again to new file with the same name. but now even that not working..
In my program I have an interface iGraphable that contains two properties: Abscissa and Ordinate. Then I have an xxxx class (actually more than one) implementing iGraphable and a ListOfxxxx class implementing BindingListView(Of xxxx).To draw graphs I have a Graph class with a property called Data whose type is BindingListView(of iGraphable).Why have I a cast exception when I pass a BindingListView(Of xxxx) to the Data property.
I have the a function that is declared like so: Public Sub Modify(Of SIMType As {New, DAOBase})(ByVal obj As SIMType)
I also have a class called Products which is declared like so:
Public Class Products Inherits DAOBase
So as you can see, if I were to call this function like so:
Modify(Of Products)(new Products())
This would not be an issue. The issue actually arises when I try to cast the object being past in to its real type. For example: both do not work. I get a Value of type SIMTYPE cannot be converted to IMS.Products error. Im assuming this is because I am using generics. Is there a way to adjust my function to allow for a casting operation like I am trying to do? In the end, what I need is a reference of the actual type (Products in this case) to the object.
Following code doesnt work and raise error "A parameter is missing. [ Parameter ordinal = 1 ]".What s wrong with it?I am developing pocket pc application in vs 2008 and sqlce 3.5 sp1.
I 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?
When you want to define a type you must say GetType(Type) ex.: GetType(string), but ain't String a type itself? Why do you need to use GetType in those situations? And, if the reason is because it is expecting a Type 'Type'... why isn't the conversion implicit... I mean, all the data is there...
I know that in WPF, FontSize = 1/96 of an inch (same as 1 pixel I think). Is the FontSize dimension the height, the width, or diagonal size of a character? I would guess it's the font height, but the Microsoft documentation doesn't really indicate what it is.
Also, is there an easy way to get the height and width of a font size?So it looks like the FontSize is the height, and the width can only be determined (without knowing the actual character) on monospaced fonts since proportional fonts have varying widths.
When I right-click on function name and then press "go to definition" it takes me to the function definition. Is there any way to do this with just one click on function name,., is there some option ,or add-on for VB? that will be perfect, fast and furious
I right-click on function name and then press "go to definition" it takes me to the function definition. Is there any way to do this with just one click on function name,., is there some option ,or add-on for VB? that will be perfect, fast and furious
I made a copy of a program so I could 'play around' with modifying it. The copy is in a different project in the same solution, plus I renamed it so there shouldn't be a conflict-so why is Go To Definition not available in the copy? It's active in the original (and other programs) but grayed out in the copy. I've rebuilt the entire solution, including the copied program-and it still doesn't work.
I have a function called Modify. It is delcared like so:Public Function Modify(Of SIMType As {New, DAOBase})(ByVal obj As DAOBase) As Boolean
You can see that this function is generic. It takes as a paramer a object that is a DAOBase or subclasses of DAOBase.Inside the modify function there is a call like so:
DAOToGP(obj)This is where the polymorphism comes into play. There are four or so subclasses I have created of DAOBase. I have written a DAOToGP() for each of these types. So in the Modify() function, when it calls the DAOToGP(obj), polymorphism should kick in and it should call the correct implementation of DAOToGP() depending on the type that I pass into Modify().
However, I get the following error:Error 20 Overload resolution failed because no accessible 'DAOToGP' can be called without a narrowing conversion:'Public Shared Function DAOToGP(distributor As Distributors) As Microsoft.Dynamics.GP.Vendor': Argument matching parameter 'distributor' narrows from 'SierraLib.DAOBase' to 'IMS.Distributors'.'Public Shared Function DAOToGP(product As Products) As Microsoft.Dynamics.GP.SalesItem': Argument matching parameter 'product' narrows from 'SierraLib.DAOBase' to 'IMS.Products'. C:Usersdvargo.SIERRAWOWIRESDocumentsVisual Studio 2010ProjectsSIMDev_2SIMIMSDVSIMLibGPGPSIMRunnerRunnersRunnerBase.vb 66 39 IMS
I am kind of at a loss here. I am not sure why it cant figure out which function to call.
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.
I'm trying to reduce code bloat, reduce errors and simplify codebehind by use of generics. In this case I'm applying generics to declaration of persistable properties. Persistance is implemented by My.Settings. Here's the code so far.
What are the situations and their associated benefits of using Generics over Inheritance and vice-versa, and how should they be best combined?I'm going to try to state the motivation for this question as best I can:I have a class as shown below:
[Code]...
Now suppose I have a repository that takes an InformationReturn argument, that has to strore different fields in a DB depending on the type of Info object T is. Is it better to create different repositories each for the type T is; one repository that uses reflection to determine the type; or is there a better way using inheritance capabilities over/with generics?
The codes below are exactly the same, except that one is C# and the other one is VB.Net.C# compiles just fine, but VB.Net throws the warning:
Interface 'System.IObserver(Of Foo)' is ambiguous with another implemented interface 'System.IObserver(Of Bar)' due to the 'In' and 'Out' parameters in 'Interface IObserver(Of In T)'
Why does VB.Net show the warning and not C#? And most important, how can I resolve this problem?
Obs: I'm using .Net Framework 4 with Visual Studio 2010 Ultimate.
I'm not sure if this is possible or not. I have a number of different classes that implement interface IBar, and have constructors that take a couple of values. Rather than create a bunch of almost identical method, is it possible to have a generic method that will create the appropriate constructor?
private function GetFoo(Of T)(byval p1, byval p2) as List(Of IBar) dim list as new List(Of IBar) dim foo as T ' a loop here for different values of x foo = new T(x,p1) list.Add(foo) ' end of loop return list end function
I get: 'New' cannot be used on a type parameter that does not have a 'New' constraint.
I have a VB6 project with about 100 custom collection classes which I want to convert to VB.Net. A typical example would be something like.
Class CAccounts Private m_Accounts As New Collection Public Sub Add(newItem As CAccount) m_Accounts.Add newItem, newItem.IdKey
[code].....
All of the collection classes in the project use this standard approach. However, not all the properties/methods of the collection classes are actually used. Most of the collection are used in "for each" loops. Keyed access using the string key is quite common. Keyed access by index is much less common.
Ideally I'd like to take a standard approach to converting these classes. I don't really want to have to review each collection and it's usage to consider whether I need a List, Dictionary, etc. Some of these collection contain 100,000 objects, and some will only contain 10. However, on the other hand I don't want to cause performance problems by using a more complex structure where a simpler option would do.
Sticking with the old style Collection. So, it would be relatively easy to convert to VB.Net But, I'd rather move to the more modern structures.Have CAccounts Inherit KeyedCollection(Of String, CAccount). Fortunately most of the classes held in the collections do have the key as part of the class (eg CAccount.IdKey above). This seems to work well. However, relatively few classes will access the colelction by numeric index. So, perhaps this is overkill if I only want keyed access by the string key?Have CAccounts Inherit Dictionary(Of String, CAccount) for the classes where I don't need access by numeric index. The problem I have with this is that all the existing "for each" loops are like "for each account in accounts". I don't want to have to change all these occurences to something like "for each account in accounts.Values". Although perhaps I can get round this by changing the default property?Have CAccounts Inherit MyCollection(Of String, CAccount), where MyCollection is my own bespoke collection. This seems a bit too much hard work.
I'm working with some XML representations of data instances.I'm deserializing the objects using .NET serialization but something in my soul is disturbed by having to write classes to represent the XML.[code]
<System.Runtime.CompilerServices.Extension()> _ Function CastAs(Of TSource As TTarget, TTarget)(ByVal array As TSource()) As TTarget() Return Global.System.Array.ConvertAll(array, Function(src As TSource) DirectCast(src, TTarget)) End Function
Public MustInherit Class Entity(Of T As Entity(Of T))
And various classes derived from it. I would like to have another class accept all of the derived objects as a property, but I cannot seeem to find a workable syntax. If it were a parameter of a sub, I could say
Public Sub Foo(T As Entity(Of T))(TheEntity As T)
I can't seem to get that to work for a property:
Public Property E(Of Entity(Of T))() As Entity(Of T)
Gives me "Type parameters cannot be specified on this declaration"
Public Property E() As Entity2008(Of T)
Gives me "Type Parameter T does not inherit from or implement the constraint type ..."Is there an acceptable way to do this or am I stuck with using a Set Sub and a Get Function?
Suppose I have an interface called IParseable(Of TParsed, TUnparsed) which requires two functions:[code]Is there a way that I can restrict TParsed and TUnparsed to be numeric types (for which operations like "*" and "+" are already defined)?The problem is that, when I try to implement my interface and define one of the functions, e.g.:[code]VS throws an error saying the "*" is not defined for TUnparsed. I understand that, since TUnparsed could be anything, but is there a way to restrict my generic such that, say, TUnparsed could only be Double, Integer, Long, etc? To require Control to be a TextBox (or maybe I don't understand that very well either). But, anyway, any idea or am I way off track? Just trying to get a hang of these interface thingies and generic types.
I have a method which requires a parameter to be passed in. I would like to use the Addhandler to call the method through a dynamically created button control's click event.
When I include () in the AddressOf, VS complains: 'AddressOf' operand must be the name of a method (without parentheses).
When I exclude the brackets, VS complains: Method '...' does not have a signature compatible with delegate...
One of the things that I think is really cool about VB.NET is how built-in functions and subs have extra help text in their ToolTips like "Expression: String expression to search for replace string." as well as the usual "Replace(...parameters...) as string" text. So are the pop up boxes with things like "CompareMethod.Binary" or "CompareMethod.Text." And finally I like how some functions and subs have different sets of parameters for the same routine. For example, New FileStream() starts with either a path (string) parameter or handle parameter, but none of the 15 sets of parameters contain both path and handle parameters. Is there a way that I can set up the classes and functions I write to use these things or do they only work with built in classes and functions? If there is a way, what are the proper names for them so I can look them up in the VS/VB documentation? I would be happy enough if someone would give me an example of them, but it would be nicer if I could go through the documentation and find out if there are other cool things that are related or near by.
I noticed in the code base I have to read that sometimes property definition includes an empty (). What's the meaning of that? And it has nothing to do with arrays.
