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].....
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]....
I have the following two tables defined...
CREATE TABLE [LogLevel] (
[Id] int primary key
,[Name] nvarchar(50) not null
[code]....
After creating a fresh endity model, I add the two tables above. When I try to build I get the following errors...
Type argument 'Inxsol.CommandPlan.Data.Model.Log.LogLevel' does not satisfy the 'Class' constraint for type parameter 'TEntity'.
Value of type 'System.Data.Objects.DataClasses.EntityReference(Of Inxsol.CommandPlan.Data.Model.LogLevel)' cannot be converted to 'System.Data.Objects.DataClasses.EntityReference(Of Inxsol.CommandPlan.Data.Model.Log.LogLevel)'.
[code]....
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
I am running a web server using VB.net and I have a bunch of pages that need to utilize similar functionality, so I was thinking of creating a shared base class that incorporates all of this shared functionality. I created a file call it SharedBaseClass.vb, and I also have a class that should inherit from this class, SubClass.aspx.vb. The Top few lines of the the parent class look like this:
Partial Class SharedBaseClass
Inherits System.Web.UI.Page
And of the child class that should inherit:
Partial Class SubClass
Inherits SharedBaseClass
Then at the top of the SubClass.aspx file it looks like this:
<%@ Page Title="" Language="VB" MasterPageFile="~/Main_SA.master" AutoEventWireup="false" Src="SubClass.aspx.vb" Inherits="SubClass" %>
Assume that all of these files are located in the same directory.But when I try to run this, I get an error:Compiler Error Message: BC30002: Type 'SharedBaseClass' is not defined.And then the highlighted error is on the line that reads: Inherits SharedBaseClass I've also tried importing the file to no avail.
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?
I've got an ASP.NET application that I installed by creating a web setup. I ran into a problem where ASP.NET wasn't registered with IIS so it gave me a "installation was interrupted" message that told me exactly nothing. Anyhow, I finally got it installed, and I can access the main page, but it's telling me that my class isn't defined. The dll is in the same directory as the Default.aspx page Here's the main error information
Compiler Error Message: BC30002: Type 'SIValidator.SIValidator' is not defined.
Source Error:
Line 4:
Line 5: <script runat="server">
Line 6: Dim validator As New SIValidator.SIValidator()
Line 7: Protected table As New arrayList()
[code]....
Is there some obscure setting that may not be set?
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.
View 2 RepliesI've got this Function:
Public Class QueryStringUtil
Public Shared Function GetQueryStringValue(Of T As Structure)(ByVal queryStringVariable As String) As T
Dim queryStringObject As Nullable(Of T) = Nothing
If queryStringVariable <> Nothing Then
If HttpContext.Current.Request.QueryString(queryStringVariable) IsNot Nothing Then
queryStringObject = CTypeDynamic(Of T)(queryStringVariable)
End If
End If
Return queryStringObject
End Function
End Class
When I try to call it like this:
Dim intTest As Integer = QueryStringUtil.GetQueryStringValue(Of Integer)("stuff")
Dim stringTest As String = QueryStringUtil.GetQueryStringValue(Of String)("stuff")
Dim datetimeTest As DateTime = QueryStringUtil.GetQueryStringValue(Of DateTime)("stuff")
stringTest gives me the error:
'String' does not satisfy the 'Structure' constraint for type parameter 'T'.
I want our other developers to not worry about having to convert a class to a structure or some stuff like that when they call this function. I just want them to be able to put a standard type in the (Of T) and have it work. I don't mind writing in extra calculations to achieve that. The other problem is I also need the function to be able to return an actual null value, so I kind of need the queryStringObject as Nullable(Of T). Which means I have to have T as Structure otherwise it tells me that won't work. So looks like if I change what T is I need to run some calculation to delcare the var as nullable or not.
I tried overloading this method so that one returns T and one returns Nullable(Of T) like so:
Public Shared Function GetQueryStringValue(Of T As Class)(ByVal queryStringVariable As String) As T
Public Shared Function GetQueryStringValue(Of T As Structure)(ByVal queryStringVariable As String) As Nullable(Of T)
And naturally it's telling me it can't do that since they just differ by return types. Is there anyway to overload this? I really don't want to have two functions.
In the following code,
For Each item in MyCollection
...
Next
What does the compiler use to determine the type of item?For example let say I have this class, which is inheriting a non generic collection,
Public Class BaseDataObjectGenericCollection(Of T)
Inherits BaseDataObjectCollection
End Class
A for each loop still infers the Item type as Object. How would I have to modify the above class to make the type inference work?
Edit: Per Beatles1692's answer, Implementing IEnumerator(Of T) kinda works. The base class already has a GetEnumerator function, inherited from CollectionBase, so I my implementation looked like this,
Public Function GetEnumerator1() As System.Collections.Generic.IEnumerator(Of T) Implements System.Collections.Generic.IEnumerable(Of T).GetEnumerator
Return MyBase.Cast(Of T)().GetEnumerator
End Function
However, the for loop still infers the type as object. But, if I change the interface implementation to this,
Public Shadows Function GetEnumerator() As System.Collections.Generic.IEnumerator(Of T) Implements System.Collections.Generic.IEnumerable(Of T).GetEnumerator
Return MyBase.Cast(Of T)().GetEnumerator
End Function
That works, the for loop gets the type inference correct. So I guess the question is now, does For Each just look for a function called GetEnumerator ?
Ok, this looks junky to me and I tried a lot of approaches; Generics won't allow me to cast the types on the fly and use MemberwiseClone() because it is 'Protected'.
Does anyone know a "short form" of doing this? I tried CType by Object.GetType on the fly; but the IDE cannot resolve the MemberwiseClone().
Private lastObj as Object = Nothing
Public Function IsObjectedDifferent(CurrentObject as Object) as Boolean
If CurrentObject Is Nothing Then Return False
[Code]....
I am trying to make a generalized function to handle if the Object is Changed; or If the values are different.
This seems like way too much code for such a simple task to me, and I have a lot of classes to compare; is there away to get the class defination dynamically so that the CType function will handle it?
I have a class called results which amongst other things has 3 internal Lists which contain 0 to n result objects each. One list has results whose answer property is integer,the next is Decimal and the last text. I many common properties like ID and I have a property on the Results class called Result which looks like this: -
Public ReadOnly Property Result(Index) As Object
Get
Select Case ResultTypeID
[code]....
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.
I have a database with a simple flyweight table referenced by another table. Let's call them, respectively, Category and Product.The Product table has several columns, one of which is a foreign key column (complete with constraint) to the CategoryID to a row of the Category table. It's simple, and I have many of them in this particular database.
I am using Linq in Visual Studio 2008 to represent this data in my application. Both tables appear as normal, and neither have anything special in their properties that would indicate the behaviour I'll describe.In the database itself, there are several Product rows which have CategoryID=1. There are two or three that have CategoryID=2. However, when the data is loaded into my application through Linq, iterating through context.Products shows that the first three have CategoryID=1, CategoryID=2 and CategoryID=3, and all the rest of the rows have CategoryID=NULL. This is not how it appears in the database. There are no other anomalies in this database.
In asp.net 2.0 I have several "dropdowns" defined using generics (examples eye color, hair color, etc). The fields are all typical; id, text, etc. All are defined as their own classes which must implement an interface I created called ILookup. However, when I try to return a List<> of this class using:[code]
View 2 RepliesThe 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.
View 8 RepliesI've just finished installing VS2010 on my computer. I have a project I built in 2003 that I'm trying to open in 2010. It went through the conversion process and generated this error: System.SystemException - The type library importer encountered an error during type verification. Try importing without class members. : System.MissingMethodException - Method not found: 'Void
[Code]...
I now have SQL Parameters set up and I'm using them to save/delete/add my data. This all works well, except when it's trying to save a combobox to the datatable it appears with the error above.Majority of my comboboxes have datasources, and the valuemembers of these are the actual list items, not the ID's of the list items.I'm not sure why this error could be happening, I'm fairly sure I've connected everything to the binding source correctly; I've checked it a few times.Does anybody know what the cause of this could be? I've looked around a bit and I haven't found much
View 7 RepliesI 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]....
I'm getting the error "Conversion from type 'DBNull' to type 'Date' is not valid."here's the line generating the error.
dtReady.Value = dSet.Tables("Db").Rows(Inc).Item("Fixed_Date")
I'm using a date/time picker control and sending the db value to it. I know that the value is null, but I don't understand why the Picker can't be blank. Is there a way to let it be blank? Or should I set up a way to check for nulls and assign today's date or something just in case?
how can I solve this error without having to fill all of my fields. Some of the fields in my database are Nulls and some have records.
Error: Conversion from type 'DBNull' to type 'String' is not valid.
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.
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]....
I have this code working. It sets the Visible property of controlToSecure to False. [Code] However I would like to get rid of hardcoding types of properties. In this case i'm hardcoding Boolean. Instead I would like to define the property type dynamically. I tried it like below but I get an error on line 2 "Type property Type is not defined". I just defined that type on the line before though? Does anyone know why this doesn't work and how i could get it to work? [Code]
View 3 RepliesI am getting the error "Conversion from type 'DataGridViewTextBoxCell' to type 'String' is not valid." When trying to display a cell from DGV in a listbox.I have my variable for the cell reference as follows:
Dim a As Object
a = DataGridView1(4,1)
To insert it in the listbox as follows:
lstLetter.Items.Add(String.Format(a))
I tried:
lstLetter.Items.Add(a)
This will not actually display the entry inside the referenced cell, it shows this in my listbox instead:
DataGridView TextBoxCell { ColumnIndex=4, RowIndex=1 }
how I need to convert this to display.
I was tried to get quantity from db make use of the selection in list box. I got answered with listbox1. If i selected the item in listbox1 the quantity would appear in textbox1. But in this same code will not work for listbox2 with textbox4.. Here i given the code...
$Con.open()
$Dim cd as new oledb.oledbcommand("Select Quantity from tlist where tool_name"& "'"listbox2.selecteditem & "'" & "", con)
[Code]....
Here i got the error as "Conversion from type DBNull to type string is not valid"
This is my
[Code]...
This is my error: Operator '=' is not defined for type 'FileInfo' and type 'Boolean'.
I've been getting this error when pulling data from a recordset. It is coming from a null entry and as a newbie to VB2008 I'm not sure how to get around this.
here is my code lblShipping.Text = reader("CARRIERCODE")
the error:Conversion from type 'DBNull' to type 'String' is not valid. Basically what i'm attempting to accomplish is to see if there is anything in that field. If so put it into the text box if not leave it blank.
I have a delegate and its event in C# as below:
public delegate UsernameCredentials UsernameRequiredEventHandler( object sender, string endpoint );
public event UsernameRequiredEventHandler UsernameRequired;
On Converting the above code in VB.Net as follow :
Public Delegate Function UsernameRequiredEventHandler(ByVal sender As Object, ByVal endpoint As String) As UsernameCredentials
Public Event UsernameRequired As UsernameRequiredEventHandler
I am getting error on the above line saying that "Events cannot be declared with a delegate type that has a return type".I understand that this is not supported in VB.Net.
Is it possible to have an argument of any type? Here's what i mean:[code]
View 3 Replies