I have two custom objects.On of them inherits the other one, appends few more properties and methods, ovverides some other.When I try to cast the Parnet Object to Child I receive an error that it could`nt be done.
View 1 RepliesI've got a project called Service.Inside the project, i've got 2 windows classes.ClassA is the main windows class which opens up when I run the program.On ClassA, I've got a button which, when I click it, opens up ClassB which is the other windows class. Inside the button's eventhandler (click), I've got a string which contains the name of ClassB's class ie "ClassB". I will probably get this from a table. Is it possible to initiate the object ClassB without using if statments to check what the type of object is. In the code below, i've managed to create a o of type object, but i need to new it with the ClassB
vb.net Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
[Code]...
Unable to cast object of type 'System.Windows.Forms.ToolStripButton' to type 'System.Windows.Forms.ToolStripMenuItem'.This is the error, when I click on the bookmark(When I add the bookmark, It's a non-clickable menu item; the next time i debug it, it becomes a clickable url(button)
Private Sub Form1_Load(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles MyBase.Load
...
Call minginimi()
End Sub
[code]....
I have an object that inherits from an interface. I can create and return the following:
Dim o As IRequest
o = New Request
Return o
This works fine. Now I want to return a List(Of Requests), so I try the following:
Dim o As List(Of IRequest)
o = New List(Of Request)
Return o
The error below is being given on o = New List(Of Request)
System.Collections.Generic.List(Of MyObjects.Request)' cannot be converted to System.Collections.Generic.List(Of MyInterfaces.IRequest)'.Consider using 'System.Collections.Generic.IEnumerable(Of MyInterfaces.IRequest)'
i have the following code which walks through an Excel file and this works fine note that the following line does work well (folder is being set earlier in the code)
[Code]...
Okay, so I have a Generic IList of custom objects that I want to use as a datasource for a repeater.
Dim productRows As IList(Of MyCustomObject)()
'fill list with data
rptResults.DataSource = productRows
[code]......
Here is a test program I wrote to explore a facet of object casting ...
Module Module1
Sub Main()
Dim class1 As MyBaseClass = New MyBaseClass()
Dim class2 As MyInheritedClass = New MyInheritedClass()
Dim class3 As MyBaseClass = Nothing
[Code] .....
The problem comes with the TryCast statement on class3. My intention is that class3 remains as a baseclass, but when the TryCast is applied, class3 morphs itself into an Inherited class which is not what I wanted. So is there a gap in my OOP/VB.NET knowledge and this action is legitimate or should class3 still be regarded as a base class?
Can you define this :
Class
Object
Inheritance
Polymorphism
Abstraction
And could you make it easy to understand I'm having a hard time to understand those terms.
I have been learning vb.net for about 6 months now and I red few books about basic visual programming as most to them have information about the basic concepts like what is Object oriented programming, subroutines, functions ,inheritance etc and bit about ADO connectivity to database. Having said all that I think I have good concepts about all these things but now I want to proceed further but can't find appropriate text books or online tutorials.
View 2 RepliesI've got a piece of code in a project (MyProject) that contains early bound object from a referenced assembly (We'll call it CommonAssembly):
Dim myObject As CommonAssembly.MyEarlyBoundType
now I have another assembly that is dynamically loaded because it is not present in all projects:
Dim myLateBoundObject As Object = AppDomain.CurrentDomain.CreateInstanceAndUnwrap("Utils", "Utils.MyLateBoundType")
MyLateBoundType derives from CommonAssembly.MyEarlyBoundType, and I want to cast myObject to myLateBoundObject and then programmatically invoke the additional
[Code].....
I am constructing a collection of objects, and need to use inheritance on a base class - I have been trying for hours in various ways and can't get this to work whatsoever - the error is always "Object reference not set to an instance of an object." The idea in the example below is that an object is instantiated, and within that lies a collection of Students when I try to access the oDemo.Students(0).Name property the error is raised. Otherwise the object appears to have instantiated OK.Here is the code being used to instantiate and access the class (from ASP.NET).
Dim oDemo As New MyDemo.Students
lblTest.Text = oDemo.Student(0).Name
Here is the sample code from the class library:
[code]......
i had a class called Tag with a structure like:
public class Tag
private _members
public properties
public shared database_methods
end class
this class was tailored for mysql database. i'm currently adding access 2007 support so i split tag into tag and tagdata with structures like:
[Code]...
I'm trying to write a (WPF) program with Option Strict on, but I have a problem.
I have a Canvas with a background image, and I want to use the coordinates of where the canvas was clicked to determine what should happen next. (Something like this)
Dim p As Point = e.GetPosition(DirectCast(sender, Canvas))
Dim imgColorMap As System.Drawing.Bitmap = My.Resources.ColorMap
Dim c As System.Drawing.Color = imgColorMap.GetPixel(p.X, p.Y)
This gives me the error: "Option Strict disallows implicit conversion of 'Double' to 'Integer'" for p.X and p.Y I have tried several things, like Math.Round but strangely enough that also returns a double.
How do I cast/round these Double values to Integer, so I can use them in my GetPixel method?
I am a VB6 programmer learning VB.Net and am having trouble with the following concept.
[Code]...
I have a base object, with a event that can be triggered by multiple methods.Then I created a child object that inherits that base object. I want to be able to trigger that event in the new object; but I can't use RaiseEvent to raise a base-object's event.To get around this, I created a small method in the base object that takes the argument for the event and I just use it to trigger the event. Is this the proper way to handle this situation? Similarly, I could Shadow the event with a duplicate one in the child object.Is there a standard way to handle events across inheritance?
View 2 RepliesI've not played with inheritance myself much as I've never really had a need to, but now I have a situation which to me seems the ideal time to learn. I'll explain:
This is a WPF application but that shouldnt make any difference to this question. Basically, I have asearch window that retrieves data from a database - I want this one search window to be able to retrieve any item (business object might be a better word than item) from the database and display the relevant data, rather than having a separate window for each 'type' of item in my program. So I have got 3 classes at the moment, ComputerAudit, ConnectionAudit, and SoftwareAudit and I want my one search window to be able to display any of these items in the listbox. Obviously there would only be one type of item displayed at once, so there wouldnt be a computeraudit item and a connectionaudit item displayed in the list at the same time, but there could be several computeraudit items displayed.
So I thought I could create a base class just named Audit and have those 3 classes I mentioned inherit from that, then I can specify the arguments to methods I am using as just being of type Audit (rather than using a specific type like ComputerAudit or SoftwareAudit) because then I should be able to pass around any of these items which inherit from Audit right? Well that doesnt seem to be the case so I'm wondering if I have misunderstood inheritance.
The problem I'm having specifically is that I have some methods which need to be able to accept any of my Audit subclasses but if I specify a generic List(Of Audit) then it wont let me pass in a List(Of ComputerAudit) for example. Is this because I'm using a List or am I just doing something fundamentally wrong?
EDIT: Found this page which confirms my suspicions that this is more to do with the List than general inheritance:[URL]...
I am having trouble getting inheritance to work with the VB 2008 Express entity classes. I am a beginner with VB.Net and self-taught in VB6.0.I am able to pull data from an SQL Server data base into my application using the O/R designer. The data can be successfully queried using LINQ to SQL, either returning a single record, or multiple records or an entire table as a collection of the enty class type (so the problem is not with LINQ queries).
View 2 RepliesIf I declare and instantiate an instance of class B within class A, how do I make instances of class A member objects/variables accessible from class B?
View 11 RepliesIn my application i will use a customized datagridview for all the application, so instead of adding the normal datagridview and changing the properties, i created an user control and changed the inherited to datagridview... This have a problem i can't use the drag and drop...
[Code]...
The issue is when I try to add a new item to the ArrayList with the following code, it gives me an error:
vb Private Sub btnLabelAdd_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles btnLabelAdd.Click
Dim result As String = InputBox("New Filter Label:", "Label List")
[CODE]................
Object reference not set to an instance of an object.
I'm not really sure what I'm supposed to be doing with this. It's a new setting I just added and it's empty, so I'm not sure if that has anything to do with it or not. Anyone know what's going on and what needs to be done to get it to accept a value and not want to be "initialized"?
I have recently gotten my hands on a free, open-source IMAP connection API.So far, I have been successful in creating a connection to one of my accounts.Where I'm getting stuck is retrieving folders and/or emails from those folders.Does there happen to be anyone here that is familiar with this API, or even Gmail (particularly the folder structure for IMAP)?
If not, here is a link to the DLL that is listed on sourceforge and the company's website that created it (if you feel like testing):
Koolwired
Sourceforge - Koolwired API
I have created a test account so feel free to use the code below without worrying about username/password issues; I'll just delete it when I'm done with it.Here is the code I have made so far for making a connection:
Dim gSession As New Koolwired.Imap.ImapConnect("imap.gmail.com", 993, True)
Dim gAuthenticate As New Koolwired.Imap.ImapAuthenticate(gSession, "imap_test@serysoft.com", "imap_test")
Try
[code]....
When I run that code, I get an error that states:System.NullReferenceException: Object reference not sent to an instance of an object. (The bold line in the above code).
Now, I'm not sure exactly what that means. Does that mean it tried to access the server and "INBOX" doesn't exist so it gets returned a NULL value? Or is it possibly the coding itself?Maybe the Gmail folder system is weird due to the fact they use labels (even though from what I have read online, the labels act as the folders in the IMAP system).
What is the problem in below code.
d Public Sub filltextbox(ByVal dlist As String) Dim tb As TextBox = CType(Page.FindControl(dlist), TextBox) tb.Text = "hello" End Sub
Error : Object reference not set to an instance of an object.
look after the error i'm having.
module1.vb
Imports System.Data.SqlClient
Module dbconn
[code]....
I create one function to run any select query. and return the OdbcDataReader type.But some time if there is no data it through error : Object reference not set to an instance of an object I need to know how i can control if there is no data.
Public Function Select_From_AnyTable(ByVal sqls As String, ByVal ConStr As String) Dim conn As OdbcConnection conn = New OdbcConnection(ConStr) Dim cmd As OdbcCommand = conn.CreateCommand() conn.Open() cmd.CommandText = sqls Dim reader As OdbcDataReader = cmd.ExecuteReader While reader.Read() Return reader End While conn.Close() End Function Dim ei As OdbcDataReader = Select_From_AnyTable("SELECT loginname from usertable limit 1", conStr) msgbox(ei.item("loginname "))
If there is data it work well but if no record found it through the error.
Is there a way to convert a DataGridViewRow object to a DataRow object?
View 2 Repliesi have drawn on a e.graphics object and now want to transfer the drawn stuff onto a bitmap object how can i do this?
View 2 RepliesLike every other program that you make when you code a button to open the next form it should open right. Well not in my case. I don't understand the problem that Visual Basics is not seeing my next form that I'm trying to open. When its in the Solution Explorer plain as day. Error below.An error occurred creating the form. See Exception.InnerException for details. The error is: Object reference not set to an instance of an object.show is not set to a object. All its doing is opening the next form. Ive use this code over an over. Now its giving me this C.O.S. error.
View 27 RepliesBasically all I am trying to do is to insert data entered in a text box(description) on the application form into database(sql2008) in vb.net. The vb code I wrote is below:
vb.net
Protected Sub Save_Click(ByVal sender As Object, ByVal e As EventArgs) Handles Save.Click
Dim note As String = Description.Text
[code]....
However when I click on save button, I get following message:
System.NullReferenceException: Object reference not set to an instance of an object.
What in this code might be causing this??This part of the code is Hilighted as causing the error.
My.Settings.Item(Holiday_" & i) = DirectCast(Me.Controls("ComboBox" & i.ToString), ComboBox).SelectedItem
Public Sub btn_Update_Click(ByVal sender As System.Object, ByVal e As System.EventArgs)
[code].....
i have a class call it clsFamily this class contains properties that make up a family object. This class works fine with no issues. Now i need a new class (called MyAccount) which contains 3 properties, an ID a user name and a clsFamily object. I have declared both classes as Friend from within my globals Module and define the clsFamily as family, however when i try to put this type within my 2nd class i get an error "Type 'family' is not defined" what am i doing wrong? i know i could get it to work fine by adding the ID and User Name properties to the clsFamily object but i need to define this as a new type of object as the ID and User name are not normally part of this class.
View 12 Replies