I have an object that I know was originally declared was an enum, but I need tothe specificnum type. I'm aware of the GetType method and it appears to work correctly, but I can't figure out how to go from there to a direct type comparison For reference types, you can use Typeof(object1) Is Class1, but this doesn't seem to work for value types.
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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.
I am looking for a good resource on variable naming conventions to illustrate variable type and where variables are declared. So I will have public variables, Private variables, private or local variables. I also may want to declare variables with the same name in different class code (i.e. in the code behind different forms). I am assuming good coding would dicatate a prefix for declaration location.
View 4 RepliesI am writing a scripting language which used .net for execution. Now I have written a function which accepts an object and return a set of numeric values. I wanted user to pass any numeric array (e.g. integer,single,double,long) and I could return values in that format. I mean user can retrieve value in any numeric array type rather than specifying an array type. E.g.
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i've got a custom integral type, and i want to be able to
Private Enum ENUM_Stuff As MyInteger
what i want to do: to know if there is anyway to make the above statement valid
I am dynamically declaring types (using ModuleBuilder.DefineType() which are used to allow for strongly typed data sets from a CSV file. However when the user adds or alters a column definition I'd like to remove and rebuild the data type. How I drop and recreate a type - do I have to unload the whole assembly or how is it done?
View 3 RepliesI want to create an xml output for my code, in VB6 the XMLfile is declared as type XML, how is this done in VB.Net?
View 7 RepliesJust wondering what everyone uses to name variables that relate to an already descriptive class? [code]...
View 2 RepliesI'm trying to compare two variables of type nullable(of boolean) in VB.NET 2010. One of the variables has a value False and the other is Nothing. Now I was expecting the following expression to evaluate to true, but this is not the case:
Dim var1 as nullable(of boolean) = False
Dim var2 as nullable(of boolean)
var2 = Nothing
[Code].....
Why don't I see my MsgBox? How should I compare two nullables (of boolean)?
What happens if I do: Dim x As New Int32? Is a object of int placed on the heap? If it is, maybe your application would be able to access global variables faster if they were reference types.
A global variable as an value type should be somewhere at the bottom of the stack most of the time and it might take more time to get to this then to get a object from the heap. Unless it's the same story with the pointer of this object is also at the bottom of the stack of course.
I'm trying to create an object Of a specific type. I've got the following code, but it fails because it can't cast the new table object to the one that is already defined. I need table to start of an IEnumerable type so I can't declare is an object.
Public sub getTable(ByVal t as Type)
Dim table As Table(Of Object)
Dim tableType As Type = GetType(Table(Of )).MakeGenericType(t)
[code]....
is there a way of changing a variable type at runtime?
<pre-question blab>// skip if you want Might as well consider me new, as I haven't programmed in years, and that was only tinkering in Java. Trying to get back on track a bit, so starting with VB to get the feel going to continue learning. I don't mind putting in the effort to learn and look up, I just am not 100% sure what I should be looking into at the moment... Old programming I did was nothing advanced, only little things like calculators, notepad-esque writers, and that sort.</pre-question blab>
I'm BASICally wanting to know what I should look into for saving multiple variables of a custom class object to be loaded later. I've seen some things about text, and I can do that fine, but don't think it would be the proper/best way of handling things
at all. I also saw some talk of XML, SQL tables, etc. I just need a point in the right direction.
For a bit more info on my actual project, I was tinkering with a 'simple' program to allow users to create rooms/objects/etc., which will then be converted into Inform 7 language (an interactive-fiction language).The variables needing stored are objects with a number of string variables and integer variables. I need to be able to save those, then load them out later into an array of said objects.
For anyone needing a more VISUAL image of what I mean, here are a few screenshots to show you what I mean. Also, if anyone has ever used Adrift, it is (at the moment) very similar to it, but for the Inform language.
Screenshot 1
Screenshot 2
I found out that you cannot set the array size for a structure when you are making it, i.e
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I have to fix this by making a variable with type made by Structure bullet and then redimming it, i.e
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This means for every variable with the bullet type i create i have to redim. Is there a way i can set the size of .mesh with .capacity for every single variable created with the bullet type automatically?
Is it possible for a class of exposing a type for function returns, without allowing users of that class to create variables of that type? A couple usage scenarios:A Fluent interface on a large class; a statement like "foo=bar.WithX(5).WithY(9).WithZ(19);" would be inefficient if it had to create three new instances of the class, but could be much more efficient if the WithX could create one instance, and the other statements could simply use it.A class may wish to support a statement like "foo[19].x = 9;" even when foo itself isn't an array, and does not hold the data in class instances that can be exposed to the public; one way to do that is to have foo[19] return a struct which holds a reference to 'foo' and the value '19', and has a member property 'x' which could call "foo.SetXValue(19, 9);" Such a struct could have a conversion operator to convert itself to the "apparent" type of foo[19].In both of these scenarios, storing the value returned by a method or property into a variable and then using it more than once would cause strange behavior. It would be desirable if the designer of the class exposing such methods or properties could ensure that callers wouldn't be able to use them more than once. Is there any practical way to accomplish that?In formulating a question, it's difficult sometimes to draw the line between complicated usage cases, and simpler usage cases which aren't quite so important. Here's another usage case, and one closer to the one I'd be most interested in (though I'm also interested in Fluent chaining; being able to have something behave like a C++ reference to a value type would be nice, but probably too much work to bother with).I have a type which is somewhat like the Windows registry, in that it is a hierarchical collection of items, each of which may have a string value, an integer value, and/or a nested collection of items. I wish to be able to support the following types of usage:[code]As for the Fluent interface, my thought would be to have the WithXXX properties return a new instance of a derived class which shadows (not overrides!) the WithXXX properties with versions that simply modify the current instance. The return object from WithXXX would be known to be of the derived class, and would thus use the shadowed WithXXX methods, but once it was assigned to a variable, it would be regarded as an instance of the base class, so the next WithXXX would create a new instance.
C++ a stronger concept of value types than C# or vb.net, including the very useful concept of references to value types; it ensures that references to value types cannot be persisted outside the scope of the type in question. Unsafe code in C# can use pointers to value types, but they don't have the protections offered by C++ references.
"Does the selection type of variables speed up the code execution in VB.NET?"For example, I have two same exactly same projects where the first project is running with all Single variables and the other project which running with all Double variables.Is there any difference in term of the speed of code execution?This is because I'm working on a project which is very critical in term of the speed of execution. However, I'm using Double variables for most part of the code.
View 4 RepliesAfter debugging a particularly tricky issue in VB.NET involving the order in which instance variables are initialized, I discovered that there is a breaking discrepancy between the behavior that I expected from C# and the actual behavior in VB.NET.Nota bene: This question concerns a slight discrepancy in the behaviors of VB.NET and C#. If you're a language bigot that is unable to provide an answer other than "that's why you should use C#, noob", there is nothing for you to see here; kindly move along.Specifically, I expected the behavior outlined by the C# Language Specification (emphasis added):
When an instance constructor has no constructor initializer, or it has a constructor initializer of the form base(...), that constructor implicitly performs the initializations specified by the variable-initializers of the instance fields declared in its class. This corresponds to a sequence of assignments that are executed immediately upon entry to the constructor and before the implicit invocation of the direct base class constructor. The variable initializers are executed in the textual order in which they appear in the class declaration.
Contrast that with the portion of the VB.NET Language Specification concerning Instance Constructors, which says (emphasis added): When a constructor's first statement is of the form MyBase.New(...), the constructor implicitly performs the initializations specified by the variable initializers of the instance variables declared in the type. This corresponds to a sequence of assignments that are executed immediately after invoking the direct base type constructor. Such ordering ensures that all base instance variables are initialized by their variable initializers before any statements that have access to the instance are executed.
The discrepancy here is immediately obvious. C# initializes class-level variables before calling the base constructor. VB.NET does exactly the reverse, apparently preferring to call the base constructor before setting the values of instance fields.If you want to see some code, this related question provides a more concrete example of the divergent behavior. Unfortunately, it does not provide any hints as to how one might coerce VB.NET into following the model established by C#.
I'm less interested in why the designers of the two languages chose such divergent approaches than I am in possible workarounds for the problem. Ultimately, my question is as follows: Is there any way that I can write or structure my code in VB.NET to force instance variables to be initialized before the base type's constructor is called, as is the standard behavior in C#?
Planning on migrating from 1.1 to 2.0 framework.After doing the automatic vs 2005 migration, it did highlighted lot of lines: due to unused variables and functions with no return type..Is there a tool which can fix those unused variables plus function with no return types.
View 2 Repliesi 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.
I'm using VB.NET in Visual Studio 2008 in a Vista 64-bit OS. I'm trying to find an easy way (there must be one) to quickly retrieve from the registry the application file name and path to use in a Shell command to open a particular file. Specifically, I want the user in my app to be able to click on a PDF file and have the app open that PDF file using the application associated with PDF file types - Acrobat Reader, for example. Anyone have any suggestions as to proper coding & syntax for the following sequence?:
(1) Get name of .exe file associated with .pdf file type (most likely from the HKey Root Classes hive)
(2) Get path for the .exe file
(3) Shell("[pathname]appname.exe filename.pdf")
I've spent a couple of hours looking through the forums and haven't found what I'm looking for.
I've come from a Assembler and C/C++ background, so I understand the concept behind reference types versus value types in vb.net. Also, I've read Jon Skeet's article regarding references and value types and I understand all of that. My question is: How can you tell if a given type is a reference type or a value type? Is it simply that all integral types (ints, floats, etc.) are value types and all classes are reference types? (If so, where do strings fall?)
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I am currently making a server monitoring application that pings the server to check its uplink, so far it creates all the picture boxes and labels for each server, and then pings the server, although I have a picture that I want to change dependant on the result.
Below is the code I am currently using, the problem occurs with the objectname variable which allows dynamic coding, where i get a error, saying that "Public member 'image' on type 'String' not found".
Private Sub Ping()
Dim i As Integer
Dim objectName As System.Object
For i = 1 To count - 1
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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>
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I'm trying to add a new record to my database but i keep getting the message - "conversion from type DBnull to type string is not valid". I think its something to do with the Employee ID when VB attempts to save it to the database my code is below
Imports System.Data.OleDb
Public Class Add
Private Sub DisplayRow()
[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'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].....
E.g. how do I get VB.Net to statically type a local variable to be the static type of the expression on the right had side of the assignment?
View 1 RepliesI 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"
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'"?
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
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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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