Create A Function That Uses A Generic Structure?
Apr 1, 2009
I am attempting to create a generic function that the students in my introductory VB .NET course can use to search a single dimension array of a structure.[code]...
My question is: Is there a way to reference the individual structure fields in the array from inside the function? I was trying to make it generic so that the student could simply pass their array into the function - their structure may be named differently than mine and the field names may be different.
I suspect there are other ways to deal with this situation, but I was trying to keep it to just a simple single-dimension array of a structure. I don't think it is possible to do what I want, but I wondered what others thought.
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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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Oct 20, 2009
I'm sort of repeating the same steps. There's got to be a way to shorten it.I was able to shorten it before by making a generic function to create the radio buttons.This is the before the rewrite
Public Sub LoadPanels(ByVal tblClient As DataTable)
Dim count As Integer = 20
Dim tooltip As New ToolTip
Dim countName As Integer = 0
[Code]...
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May 31, 2011
Anyone want to try converting this to VB?
[Code]...
It is supposed to sort any type of object. Taken from here
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Jun 2, 2010
Question: I want to call a generic function, defined as:
Public Shared Function DeserializeFromXML(Of T)(Optional ByRef strFileNameAndPath As String = Nothing) As T
Now when I call it, I wanted to do it with any of the variants below:
Dim x As New XMLserialization.cConfiguration
x = XMLserialization.XMLserializeLDAPconfig.DeserializeFromXML(Of x)()
x = XMLserialization.XMLserializeLDAPconfig.DeserializeFromXML(GetType(x))()
x = XMLserialization.XMLserializeLDAPconfig.DeserializeFromXML(Of GetType(x))()
But it doesn't work.I find it very annoying and unreadable having to type
x = XMLserialization.XMLserializeLDAPconfig.DeserializeFromXML(Of XMLserialization.cConfiguration)()
Is there a way to call a generic function by getting the type from the instance ?
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Jun 7, 2012
I have a grid view with a lot of columns, all need to be sorted on. I have seen a few snippets out there, but I cannot get any of them to work with my example. Here is what I have so far.
Protected Sub gvSearch_OnSorting(ByVal sender As Object, _
ByVal e As GridViewSortEventArgs)
If Not Session("sort") Is Nothing Then
[code].....
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Oct 12, 2011
written a generic "LaunchForm" function? For all the menu items I have that open a form, I would like to write one function that will launch the form as opposed to writing the same code several times.
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Sep 16, 2011
I have an abstract class in VB.NET. I want all classes that inherit from this class to return whatever value makes sense. For example, it could be an Decimal, Integer, String. How can I delcare the function in the abstract base class to allow for this? Is this even possible?
[Code]...
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Oct 14, 2010
I have created a couple of simple functions in VB.NET that simply return a control of a certain type that I already know, such as HtmlInputHidden, Label, etc. That means that each of the functions is created only for that special purpose. What I'd like to do is combine all those functions into one function using generics. The common things shared by each of the functions is a control Id and a control type.What I have got so far is:
Public Function GetControl(Of T)(ByVal ctrlId As String) As T
Dim ctrl As Control = Me.FindControl(ctrlId)
If (Not ctrl Is Nothing) Then
[code]....
But the line " GetControl = CType(ctrl, T)" is giving me a compile error:
Value of type 'System.Web.UI.Control' cannot be converted to 'T'
This is in .NET Framework 2.0.
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Aug 24, 2010
I am trying to write a generic function that will check each database parameter to see if it is null, and if so, return DBNull; if not, return the object.So here is my function:
Public Shared Function CheckForNull(ByVal obj As Object) As Object
If obj <> Nothing Then Return obj Else Return DBNull.Value
End Function
[code].....
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Sep 2, 2009
I must be doing something wrong here (because really, what are the chances of me tripping over another bug in the Vb.net compiler?)I have a static generic function in .net 2.0 Vb code, I thought it was time to "upgrade" it to be an extension method, but the compiler complains with Extension method 'AddIfUnqiue' has type constraints that can never be satisfied.
Here's a trivial example that displays the same problem. The old static version (which works fine) followed by the extension method
Public Class MyStaticClass
Public Shared Sub AddIfUnqiue(Of T, L As {List(Of T)})(ByVal this As L, ByVal item As T)
If this.IndexOf(item) < 0 Then
[code].....
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Feb 16, 2011
I can create classes that use generics, however I was wondering if it is possible to apply this to a shared method rather than rely on the caller casting to the correct type.This is the method:
Public Shared Function DeserializeObject(ByVal serializedXml As String, ByVal givenType As System.Type) As Object
Dim serializer As New XmlSerializer(givenType)
Return serializer.Deserialize(New IO.StringReader(serializedXml))
End Function
I'm pretty sure this can't be done, but thought I'd check (if so Extra points will be awarded if someone can technically explain why the compiler can't do this)..
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Oct 26, 2011
My question here is, what are the negative effects of using a generic function such as this? Calling this function does work, and in a test console module, it compiles perfectly fine. I do know this is not a strongly typed function, and is %100 bad practice. But it works perfectly. The purpose of a function like this, would be to handle string input that needs to be inserted in a particular format depending on the type. I also read some other questions on this here on stackoverflow, and suggestions pointed to using (Of T) functions, and variations like that. Why not do it this way? or is there another simple way of accomplishing this without creating a whole nothing class or larger amounts of code.[code]
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Jan 18, 2011
I like to turn Option Strict On I cant figure out how to write the generic version of this function?
Public
Shared
Sub UpdateItem(ByRef
oldValue As
[code]....
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Apr 29, 2010
Currently I have written a function to deserialize XML as seen below.How do I change it so I don't have to replace the type every time I want to serialize another object type ? The current object type is cToolConfig. How do I make this function generic ?
Public Shared Function DeserializeFromXML(ByRef strFileNameAndPath As String) As XMLhandler.XMLserialization.cToolConfig
Dim deserializer As New System.Xml.Serialization.XmlSerializer(GetType(cToolConfig))
Dim srEncodingReader As IO.StreamReader = New IO.StreamReader(strFileNameAndPath, System.Text.Encoding.UTF8)
Dim ThisFacility As cToolConfig
[code]....
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Jan 13, 2011
I would like to write a generic function that would search a List(Of T) for all elements of type TFilter and return a List(Of TFilter) which comprises those elements.
I've tried this:
Public Function FilterList(Of T, TFilter)(ByVal ListToFilter As List(Of T)) As List(Of TFilter)
Return ListToFilter.FindAll(Function(z) z.GetType.Equals(GetType(TFilter))).ConvertAll(New Converter(Of T, TFilter)(Function(z) CType(z, TFilter)))
End Function
But, it gives the following error:
Value of type 'T' cannot be converted to 'TFilter'.
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Jun 4, 2012
What's the best way to handle this situation: I have this generic function
Function FieldValue(Of T)(row As DataRow,fieldName As String) As T
Return If(row.IsNull(fieldName),Nothing,CType(row(fieldName),T))
End Function
In the special case where the field value is null and T is String, I want to return String.Empty instead of Nothing.
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Jun 8, 2009
I have a following code which works fine
MsgBox(AddSomething(Of String)("Hello", "World"))
Public Function AddSomething(Of T)(ByVal FirstValue As T, ByVal SecondValue As T) As String
Return FirstValue.ToString + SecondValue.ToString
[code].....
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Jan 2, 2011
i've been trying to toy around with generics in vb.net in an example project. At the moment, it looks like this:
I have an interface called IRow (and a class that implements it as a Datarow).
A second interface is ICanGetByRow, which looks like this:
Public Interface ICanGetByRow(Of T)
Function GetByRow(ByVal Row As IRow) As T
End Interface
The function simply takes an IRow and converts it to T. Thats easy enough. Now, for easier access, i want to implement a function in the IRow interface which takes the row and converts it into said ICanGetByRow.
My interface was enhanced by the following function
Function GetObj(Of T As ICanGetByRow(Of T))() As T
You can probably see the problem. If i implemented it like this:
Public Function GetObj(Of T As ICanGetByRow(Of T))() As T Implements IRow.GetObj
Dim foo As New T
foo.GetByRow(Me)
Return foo
End Function
i wouldn't be allowed to construct a new T, and when i tried to make it work by telling the generic function that my interface has a constructor, he wouldn't let me invoke GetByRow anymore.
Public Function GetObj(Of T As New, ICanGetByRow)() As T Implements IRow.GetObj
Dim foo As New T
foo.GetByRow(Me)
Return foo
End Function
how to tell a generic function that it will get a ICanGetByRow(of T) which has a constructor
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Apr 16, 2012
I have problem about how I call a function on DLL to get data from a structure. Have a C++ example about how it's works the library, and I want to use it on vb.net. his is the working c++ example:
Declaration:
BOOL (WINAPIV* MyFun)(DWORD start1, DWORD stop1, P_RESULT pResult, PDWORD pTpNum, myCALLBACK lpFunc) = NULL;
Call:
// pStruc = RESULT structure
// TrpNum1, TrpNum is ULONG
ULONG TrpNum1=0;
MyFun(Start,Stop,pStruc+TrpNum,&TrpNum1,&myCB);
Callback:
void __stdcall myCB (RESULT *pStruc) {
printf ("%.3f", (double)pStruc->val1);
tpn++;
[Code] .....
The error is this: "Attempted to read or write protected memory. This often indicates that other memory is corrupt."
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Apr 24, 2012
I've this code, but there is a problem with setting values. I get "null object" error. how to work properly with functions.
Public Structure Results
Dim Nickname As String
Dim Result As Integer
[Code].....
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Dec 22, 2009
I want my function to return a value of a structure. The function is supposed to change the values and then return the answers in one structured value. Here is my code... as you can see it does not work... it needs a LOT of things. I placed question marks were i am really lost.
[Code]...
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May 11, 2010
I have a question: How can I make a function or sub run inside a structure when a variable in this structure changes? As example I have this function:
Public Structure Texture
Sub New(ByVal TexturePath As String)
Me.Path = TexturePath
Me.Image = LoadImage(TexturePath)
End Sub
Public Path As String
Public Image As Image
End Structure
And somewhere this happens:
Dim t As New Texture("path ooldfilename.tga")
t.Path = "path o
ewfilename.tga"
I want it to automatically load the image when the "Path" variable changes. Is the only solution making an extra sub and run that? It would really decrease my code size if it changes on variable change.
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Nov 21, 2010
Say I do this
Public Function CheckWebCamVF() As BusinessProfilesBO.VFCheck
checkwebcamVF.isactive = true
return checkwebcamVF
[code].....
I seem to be getting null referance errors using the first one.I am trying to get my code as fast and as correct as possible
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Feb 23, 2010
I have a generic repository that I communicate with my object context with. My object context has function imports that I want to be able to call through my generic repository. Currently I call them through an "Execute" function, but this is not ideal because I have to pass in my function name and parameters as strings which can cause run-time exceptions. My function imports map to complex types.
Is there a way to do something similar to:
Dim rep As IRepository(Of ComplexType)
Dim type As ComplexType = rep.Find(where:=Function(t) t.FunctionImport(parm, parm)).First()
Here is my generic repository as is:
[Code]...
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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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Jan 8, 2011
In vb.net, it is possible to design a function which can operate on generic parameters which meet multiple constraints. For example, it is possible to have a function accept as a parameter a class which inherits from Control and implements IList. This function could use "Control" or "IList" methods on such an object, and also pass the object to anything that expected a Control or an IList [note that this particular combination was chosen to facilitate a brief example, not to be a particularly useful combination].
[Code]...
This approach provides compile-time type-safety; there's no need for a cast that could fail at runtime. An alternative approach would be to pass the argument as either a Control or an IList, and have the function cast to the other. That would, however, fail at runtime if the object that was passed didn't in fact meet both constraints.
Under what circumstances is it good to use a generic function like the above, in what cases would it be better to have objects which are going to meet both constraints have a new interface like IListableControl(Of T) which would include a TheControl property that would return itself (cast as a control), and in what cases would it be better to have a generic ISelf(of T) interface, any implementor of which would be expected to provide a "Self" property that would return itself as a T?
Using multi-constrained generics, it's possible to do a lot of things without requiring any run-time typecasts, but I don't know what the performance costs are likely to be. I tried writing a short program to generate 65,536 different generic types at run-time, e.g. Foo(of Bar(Of Foo(Of Foo(Of Bar(Of Foo(...(Of Blah)) and it got pretty slow, so I can tell that the time required to handle generics isn't fixed, but I don't know what factors affect it.
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Jun 23, 2009
The idea is to expand on the existing, old, and lacking Inputbox, to allow for:1. A greater variety of types (Integers, doubles, List(Of String), etc.2. Data validation.For example, if the user wants the user to quickly enter an Integer, I want a custom Inputbox form to show up with a TextBox, which only allows Integer input. If he wants the user to choose from a List(Of String), I show a form with a Combobox instead, from which the user can then choose.
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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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Nov 7, 2011
I'm a beginner when it comes to Visual Basic coding and I need some help with an error I'm getting. I'm trying to pass a structure array to a function to figure out a student's grade. I'm getting the error that 'QuizOne' is not a member of System.Array. Here is my code:
[Code]...
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