.net - Cast To Generic Type At Runtime?
Sep 9, 2010
I'm in the process of creating a function which reflects over the properties in a class and adds them to this data structure I have. Some of the properties are generic types.So say we have DataType(Of T) that has a .Value property of type T:
Dim properties = GetType(MyType).GetFields(Reflection.BindingFlags.Public Or _
Reflection.BindingFlags.Instance)
For Each prop As fieldinfo In properties
Collection.Add(prop.Name,prop.GetValue(poco))
Next
In the collection.Add for primitive types (Integer, String, etc....) I just want to add the type... but in the case of generic I want to add the DataType(Of T).Value. I hope there is some work-around but I don't think there is a way because the type of T can not be determined at compile time right? Ideally DirectCast(prop.getvalue(poco), DataType(Of T)).Value would be possible. This is when you hoped even more dynamics appear than whats in .NET 4.0.
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Feb 25, 2011
I know about the existence of System.Nullable(Of T) Structure.I am trying to write a class to replace it: The Nullable(Of T) Class [VB code below]. But when I tested the Nullable(Of T) Class (See NullableOfTClassTest Class, Method Main) an exception occurs when using the CType operator to convert from System.Int32.Why does this happen at runtime, why isn't my Ctype operator method being called?
NOTE: code below reordered and reduced in order to hilite problem.
Namespace MyNamespace
Public NotInheritable Class NullableOfTClassTest
Private Sub New()
End Sub
[Code]...
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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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Aug 14, 2010
I have a Journal that records entries for different types: Journal(Of ParentT)
[Code]....
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May 14, 2012
I'm getting an error after sending a list to a web service.This is the code that is calling the web service:
Dim sProgramInterest As New List(Of Integer)
crmService.InsertProspectGetId(sProgramInterest.ToList)
But I'm getting this error.
[code].....
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Jan 7, 2012
And here is the code that produces the error
CODE:
How can i cast this one?
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Jan 25, 2012
I am using reflection to get an object's type, or for this issue an object that has instance properties type, at runtime and then I need to change an existing variable's type into that newly found type. Is this possible? For example, the following code does not work in the line indicated within:
Public Sub DoSomething(x As T, y As T, exp As String)
'This is a instance property on the object of a different type
'i.e. 'T.AnotherType' We need to reflect to find out what type of object
[code].....
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Feb 9, 2012
Private
Sub cmdExit_Click(ByVal
sender As System.Object,
ByVal e
[code]....
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Jul 7, 2010
I have created a Dictionary class (MyDictionary for the example). I am currently trying to pass MyDictionary into a function, filter it into a new instance of MyDictionary and pass this new instance into another method. When I am attempting to create the second instance from the filtered first instance of MyDictionary via Lambda Expressions and the ToDictionary Method, I am getting the following error:
Unable to cast object of type 'System.Collections.Generic.Dictionary`2[System.Int32,System.String]' to type 'MyDictionary'. I have simplified the example and recreated it in LINQPad and am getting the same error.
Here's the simplified version of my code:
[Code]...
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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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Jun 10, 2010
how Inheriting List(of T) should work.It seems like what I have below should work but at runtime I get the error:[code..]
If I want to cast a List(of x) to the class xlist, how should I do that?[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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Apr 10, 2012
I'm using EF 4.3.1 in VS 2010 (.Net 4.0) to load a number of reference tables from a database in order to bind them to controls in a WinForms app.At form load, I'm pre-fetching the data so that it's stored locally, and I'm creating a dictionary of BindingSource objects that I can use to bind the local data to the controls.The intent is to minimize the impact of the EF's self validation on a cold query in order to load forms faster and improve UI responsiveness.I've written code to create and fetch the BindingSource object for a given DbSet collection as follows:
Private _dictBindings As New Dictionary(Of String, BindingSource)
Private Sub ValidateBinding(Of T As Class)(ByRef DbCollection As DbSet(Of T))
Dim strClassName As String = DbCollection.[GetType]().GetGenericArguments(0).Name
If Not _dictBindings.ContainsKey(strClassName) Then[code].....
However, I'd like to call ValidateBinding on all DbSet collections in the Model on startup, and I'd like to use reflection to iterate through the available collections in the context because we're currently loading 66 tables and could add more later.I've written the following code:
For Each propSet As PropertyInfo In Db.GetType.GetProperties(BindingFlags.Instance Or BindingFlags.Public).Where(Function(P) P.PropertyType.IsGenericType)
ValidateBinding(propSet.GetValue(Db, Nothing))
Next
but it won't work as propSet.GetValue() returns an Object instead of DbSet(of T).I also can't cast the object to a DbSet of the appropriate type, even though I know the type through reflection.I don't have access to the C# Dynamic type,and I know it's a pain to mix generics with reflection, but is there a solution for which I can pass in a reflected DbSet to my functions?Perhaps something using Method.Invoke?
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Jan 28, 2012
when view in browser, i got this error: Unable to cast object of type 'ASP.webform1_aspx' to type 'System.Web.UI.WebControls.Button'.
how should i solve this problem?
Line 7: If Not Page.IsPostBack Then
Line 8: Dim rowIndex As Integer = 0
<b>Line 9: Dim btn As Button = DirectCast(sender, Button)</b>
[Code].....
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Apr 19, 2010
I had write code (just for learning), the codes :
dim Temp as string
Temp = Recordset("
Table_Field")
but, when I start Debugging the error messages "Unable to cast object of type 'ADODB.InternalField' to type 'System.String"
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Apr 13, 2011
I am implementing IMAPI2 into my vb.net project but ran into a wall. I am getting the message Unable to cast object of type 'IMAPI2FS.FsiStreamClass' to type 'IMAPI2.IStream' when trying to start the burn. I googled around and found this is something that microsoft hasn't fixed.. which basically renders IMAPI2 useless in vb.net.
I found a post on codeproject.com by eric hadden who combined the IMAPI2.dll and IMAPI2fs.dll into an c# interop file. I also see the IBURN interop in microsoft SDK samples. I'd like to use either, but it's in c# and I'm using vb express. Does anyone know a way to get the interop into visual basic or a way around "Unable to cast object of type 'IMAPI2FS.FsiStreamClass' to type 'IMAPI2.IStream'"?
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Jun 1, 2009
I'm having a problem with converting from one source type to a destination type. I have a form with 2 buttons (button 2 uses the OpenFileDialog to have the user open an excel file set to NewFile),(button 1 takes the contents from specific cells in NewFile and arranges them how I need into oXLApp1).
The error I get is "Unable to cast object of type 'System.IO.FileStream' to type 'Excel.Application'." in line 14 of the code below.
Public Class Form1
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
[Code]....
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Mar 19, 2009
I'm new to VB 2005, the code below is actualy coded from VB 6 and just converted it to VB 2005. I'm having trouble with line that's on bold letters.In VB 6 this works just ok. By the way the error message is "Unable to cast object of type 'System.String' to type 'ADODB.Connection'." [code]
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May 24, 2011
I can't cast my objects. I get: "Unable to cast object of type 'ClassA' to type 'ClassB'".
The service Class:
Public Class svc_Insp
Implements Isvc_Insp
Public Function Test(ByVal pm_income As ClassC) As String Implements Isvc_Insp.Test
[code]....
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Mar 8, 2009
Could anyone assist me in solving my problem ? My code was written in VB (VS 2003.)I got this error: System.InvalidCastException: Cast from type 'DBNull' to type 'Integer' is not valid. in my code.Here is the code line where I am getting the error: LeadCampusID = CInt(.Item("mkCampusID"))I fixed the error by making the changes in the code as :
If Not IsDBNull(.Item("mkCampusID")) Then
LeadCampusID = CInt(.Item("mkCampusID"))
Else
[code].....
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May 14, 2009
Unable to cast COM object of type 'System.__ComObject' to class type 'rjsDocMan.Folder'.Instances of types that represent COM components cannot be cast to types that do not represent COM components; however they can be cast to interfaces as long as the underlying COM component supports QueryInterface calls for the IID of the interface.The code where it is flagging the error is:
<div style="color: Black; background-color: White;">
treeview += AddChildren(Session("DocMan").RootFolder)
</div>
[code].....
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Dec 18, 2009
I saw this thread and I had simple answer in mind. To use custom enumerator class. So I was trying to make one for that guy, which would have one more property to check whether its has reached end or not. It would also provide current position.I'm getting an error "Unable to cast object of type 'SZArrayEnumerator' to type 'WindowsApplication1.myEnumerator'." at the line 6 [see below].However, return type of values.getEnumerator says its IEnumerator. [code]
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Feb 19, 2012
Columns 0 & 1 are filled from a DataAdapter from Access Database and three are added. I had this working, but I changed it to check for the column "Feed" so I could add several Locations. At first this worked,but I did someething in perfecting it and it now fails after filling the first row of the datagridview (dgvFdMed).I ran a check and the table LotsTab has 8 rows filled. Column 1 & 2 are strings and the database appears they are fine. The added columns have just been created with no value. My plan is to enter the values and then use the data from the grid.
Private Sub sfillGrid(ByVal Loc As String)
Dim i As Integer
Dim column As DataGridViewColumn
[code]....
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Dec 8, 2010
I have 2 Child forms inside a parent. For example, FrmChild1 contains a "Friend Sub" I wish to call.I would like one of the child forms to call that sub from another child form (we will call it FrmChild2. The following code works, but when it's done going through the "For Each", I get a "Invalid Cast"
' THIS CODE IS IN FrmChild1
For Each mFrmChild2 As FrmChild2 In FrmParent.MdiChildren
mFrmChild2.GuestRefresh(False)
Next
Error after calls are made:"Unable to cast object of type FrmChild1 to type FrmChild2.
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Dec 22, 2010
I have a series of API calls that are returning J# data types. I have been able to convert most of the data types (Integer, Boolean, Double, Float, etc) just fine.What I need to do now is convert a java.Util.Collection to a VB .NET collection (ArrayList)
Here is my attempt:
Public Function MakeDotNETCollection(ByVal javaCol As java.util.Collection) As Collection
Dim dotNetCol As Collection
[code]....
I keep getting a runtime error "Unable to cast object of type 'AbstractListlistIterator' to type 'System.Collections.IEnumerator.
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Jun 1, 2012
I am building a software which will be used to create a remote desktop connection. However I'm getting this error:
Unable to cast COM object of type 'System.__ComObject' to interface type 'MSTSCLib.IMsTscNonScriptable'. This operation failed because the QueryInterface call on the COM component for the interface with IID '{C1E6743A-41C1-4A74-832A-0DD06C1C7A0E}' failed
due to the following error: Δεν υποστηρίζεται τέτοια διασύνδεση (Exception from HRESULT: 0x80004002 E_NOINTERFACE)).
[Code]...
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Feb 24, 2012
I am using a background worker and am attempting to use the following code. However I keep getting this error on i "Unable to cast object of type 'ObjectCollection' to type 'System.Array'."
Private Sub btnVerify_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnVerify.Click
myArray = listProxies.Items()
BackgroundWorker1.RunWorkerAsync()
End Sub
[code]....
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Nov 9, 2009
I have given reference to Microsoft HTML in COM (am using VB 2008)
"Unable to cast object of type 'System.Windows.Forms.HtmlElement' to type 'mshtml.IHTMLElement'."
I want to retrieve all the properties like the class name, html id of every object in the web browser. I am getting the above exception when i try to direct cast it.[code]...
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