If i have an object that implements an interface (and don't know the exact object) i can call a sub (DoSomething) by going:
vb
Dim iObj = trycast(something, iInterface)
if iObj isnot nothing then
iObj.DoSomething()
end if
How can I do this for a Generic? such as...
vb
Public Class TestClass(of T)
Public sub DoSomething()
....
end class
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.
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.
I've hit a problem with the way I am using generics and I suspect that my design isn't quite right. I have a base class
AbstractBaseClass
inherited by
InheritingOneClass
[code]....
I have a generic list IList(of T as AbstractBaseClass) which I am populating with instances of the various inheriting classes. Now I can cycle through the list BUT depending on which subtype the item is, I want to pass the item to various functions (or instantiate various classes) which access properties/methods of the inheriting Class. I don't really want to have to use a Select Case and list all the potential types of the Inheriting classes. Is there a mechanism I can put in place to automate this?
I have a Journal that records entries for different types: Journal(Of ParentT)
[Code]....
I am trying to construct a generic interface class with generic functions. My goal was to use this to implement multiple worker classes for database interaction that have the same basic functionality. Each class will deal with different object for example, category, product or supplier but unless the the functions in the interface are generic that this won't work.This is the interface code that I have but I don't know if I have done it correctly. [code]
View 2 RepliesI 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.
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]...
I have been using a pretty slick generic invoke method for UI updating from background threads. I forget where I copied it from (converted it to VB.NET from C#), but here it is: Public Sub InvokeControl(Of T As Control)(ByVal Control As t, ByVal Action As Action(Of t))
[Code]....
I can do this without problem.
Class A
End Class
Class B : Inherit A
End Class
Dim Obj1 As A = New B
I did post this in my thread about webcam but its nothing to do with webcam issues, the code for the webcam is working perfectly now I am instead now having an issue saving an image file from a picture box.
I don't mind how its done or whether its bmp/jpg (jpg would be better for te compression) but This orginally did work now I keep getting this error that I have never come across before and can't find much information on the error.Error Message:A generic error occurred in GDI+.
[Code]...
i just encounterd an error gdi+ when saving same image back to database.im using this code to get image from db
'Stream object containing the binary data
Dim ms As MemoryStream
ms = New MemoryStream(CType(Me.DataGridSearchView.SelectedCells(10).Value, Byte()))
frm.Picture1 = Image.FromStream(ms)
ms.Close()
frm.Picture1 is a property of image type from another class.and this my code to update image back to db
If Not Me.PictureBox1.Image Is Nothing Then
Dim custPic as Byte() = Nothing
Dim ms As MemoryStream = New MemoryStream
[code]....
there is no problem if i changed the image before saving it back to db,it gives error if you will not change the image before saving it back to database..
Is it possible to have a sub that is triggered when any control of a specified type is clicked (or some other interaction), and then within the code of that sub, determine the sender and depending on the sender perform an action?For example, you create buttons dynamically, and assign them a name based on a counter that tells the number of buttons on the form. Now you click on a button, but there was no code written for 'button123.mouseclick' specifically. Instead, you get the name of the sender (button123) and you do something specific to that button.[code]
View 5 RepliesSay I have a generic list that is a list of a structure.
[Code]....
I always get an error that it's a value and cannot be set. Is there a way to change it without having to make a local copy of the item, then set the item on the list to that local item?
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.
View 8 RepliesTo the point: I need to transfer a custom object's event through a generic collection object containing these items so that any class using the collection can see that changes were made to one of the items in the collection.
I.E. An item event that triggers a collection event
[Code].....
Due to the application requirements, I need the Collection and Items to send immediate notice of various changes that occur to the Collection Class and its items. I've already got my events set-up regarding for the Collection Class, but I'm struggling with coming up with a workable solution for raising events for the items.
I've got an event for the DeviceLayer item set-up, but how do you transfer that event through the CollectionClass so that any other class using it will see that there was a change to one of the items in the collection?
how to find a value in the System.Collections.Generic.List.I have:
Private ids As New List(Of Byte())
ids.add(New Byte(){&HA8,&H0F})
ids.add(New Byte(){&HFF,&H03})
ids.add(New Byte(){&H10,&H00})
I would like to find for example: &H10,&H00 in that list and if there isn't the stuff I wan't to find then how do I know that?
so I have a generic list in a console application. Dim Channels as New List(Of Chatroom) Chatroom is a structure. But I have multiple classes, threads, and timers looping through this list, sometimes at the same time, but it always seems to raise errors because the number of items in the list gets changed while one of the other classes/threads/timers are looping through also. Is there any way to allow only one to manipulate it at a time?
View 8 RepliesI've written a simple application to encrypt an image (jpeg file) based on a password as a challenge to a mate of mine who reckons he's an ace hacker.I can encrypt the image no problem but when I try to save it using
[Code]...
I get "a generic error occurred in GDI+" raised. Googling reveals a few hits for this problem but seemingly mostly related to using databases rather than the file system.
Has anyone come across this? I don't want to paste all my code here in case my nemesis is watching, however basically I'm getting a reference to the PictureBox's Image property and manipulating the pixels using GetPixel and SetPixel, and then setting the picturebox's image property = my modified bitmap.
I understand that the error is generally related to the bitmap not being ready to be saved - is there anything specific I need to do to "close" the bitmap so it can be saved?The strange thing is that I'm sure this was working earlier today and now seems to have arbitrarily stopped working.
At the moment we're are considering writing a number of .Net web services to export/import data between sites. There are various different types of data involved, relating to multiple database tables. I could write various web services to receive the data being sent, for example
ImportSomeRecord(field1, field2, field3)
ImportSomeRecord2(field1, field2)
ImportSomeRecord3(field1, field2, field3, field4, field5)
and so on...
There could be about 40 of these services, and it's also possible that the fields may change i.e. new fields may be added. The client would be a VB6 application that would call the remote web service, and let that web service update the remote database. The web services will be written in VB.Net 2008.
Would it be advisable to replace all these web services with a single generic service e.g. ImportRecords(recordtype, blobofdata). I think this can be done in theory by just passing an XML string as the blob of data and letting the web service unravel this depending on the record type, but is there actually any advantage to this, and is it good practice to do so? I've read somewhere that passing XML chunks in this way, as a single parameter, isn't recommended, and I can see this also seems to be somewhat contrary to standard web service usage in that in effect I'm bypassing the web service definition.
This is just a Translation question. But how do you write a the following C# code in vb.net My problem is that i don't know how to rewrite the this part of the generic T. C# code i want to translate
public static void ShouldEqual<T>(this T actualValue, T expectedValue) {Assert.AreEqual(expectedValue, actualValue); }
[Code]...
In VB.NET when i define a subroutine (or function) , while declaring arguments , a list comes out. Having values ByVal,ByRef,Of,Optional, and ParamArray. Of these five lists , four are better understood except "Of". I searched and found that "Of" is used for Generics .Generic Class or Generic Method.
But i did'nt find any procedure that how to create and use Generic Method in VB.NET. I found same in VB.C# language.
Public Function CastToT(Of T)(ByVal GenericType(Of Object) data) As GenericType(Of T)Return DirectCast(data, GenericType(Of T))End Function
The above clearly does not work. Is there any way to perform this cast if I know that all objects inside data are in fact of Type T?
I have a method where I'm taking a generic object and using TypeOf to check what has been passed through. Now I would like to pass it a List(Of T) (T being anything) and no matter what T is I'd like to do the same thing to this list. I tried the following:
public sub foo(ByVal obj As Object)
if TypeOf obj Is List(Of Object) Then
'do stuff
end if
end sub
but this doesn't seem to work if I pass it List(Of String), say. I suppose that List(Of Object) and List(Of String) are being treated as different objects, but I thought that since String is an object, the comparision might work.
Now I realise that this is as ugly as sin and I'm better off overloading the method to take List(Of T) as its parameter, but I'm mostly asking out of curiosity: is there a way of comparing the types List(Of Object1) and List(Of Object2) and getting a positive result, since they are both just List(Of T)?
Anyone want to try converting this to VB?
[Code]...
It is supposed to sort any type of object. Taken from here
Consider the following extension method:
<Extension()> _
Public Function Satisfies(Of T)(ByVal subject As T, ByVal specification As ISpecification(Of T)) As Boolean
Return specification.IsSatisfiedBy(subject)
End Function
This works as expected if subject is the exact class being operated on by the specification. However, if the specification is examining the super-class of T, this extension will not work unless subject is explicitly cast to the super-class. Is there a way I can avoid this? So far, the best I've been able to come up with is:
[Code]...
Since I (apparently) can't get this to work exactly as I'd like in VB.NET due to limitations in the language itself, is my second attempt the safest/most efficient way to do this?
I have some code that takes a screen capture of my monitor. This code seems to work perfectly OK and can take multiple screen captures, apart from when I do a Print Screen using the keyboard or open SnagIT 8, when I then try to run my code again I get an error "A generic error occured in GDI+" I am at a bit of a loss, I have had a look on the internet, but everything I seem to find appears to be related to web apps. and access permissions. This is a window based application and therefore can not seem to find an answer.[code]
View 1 RepliesI've got the coding below to make a screenshot and store it in a jpg file`.. this works fine on my computer with vb.net installed. However when I tried running it on an other computer it gave me this exception:
'a generic error occured in gdi'
'the coding
PHP
Dim screenImage As New Bitmap(My.Computer.Screen.Bounds.Width, My.Computer.Screen.Bounds.Height)
Dim g As System.Drawing.Graphics = System.Drawing.Graphics.FromImage(screenImage)
[Code]....
I've read on internet that this is a write permission issue or it has something to do with the stream. Anyway I dunno how to alter the coding so that every user can make a screenshot.
I am writing a VB.NET application which captures an image from a webcam and saves it as a jpeg. I have a button which captures the image and successfully saves the image. However when I click the button again to save the image as the same file I get the following GDI error[code]....
View 4 Repliesi save the PictureBox Image to the Sql using the following code
Private Function convertPicBoxImageToByte(ByVal pbImage As Image) As Byte()
Dim ms As New System.IO.MemoryStream()
pbImage.Save(ms, System.Drawing.Imaging.ImageFormat.Jpeg)
[code]....