Listbox, Objects, Inheritance And Polymorphism
Jan 31, 2012
I wasn't quite sure how to label this but that should cover it all. I am using Linq to Sql classes to query a SQL Server table. That part is working fine. I'd like to add the records to a listbox and not just text. I can do this and it works. To get it to display something meaningful in the listbox, I have to override the ToString() function.
So, I've taken the base class tblVendor and created a new sub class tblVendorListObject that inherits tblVendor and overrides ToString to return Me.vendorName. I then use a foreach loop to iterate through the records returned by the query. Next, I create a new instance of tblVendorListObject and attempt to assign the current item in the foreach loop to it.
[Code]...
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Mar 8, 2010
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.
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Feb 16, 2012
I'm trying to create a class for storing data on People with another class to store their Bank Transactions.Ideally, this all be hidden away and leave only simple statments, declarations and functions available to the programmer.[code]I know this is possible as these exist in the Listbox Class though can't figure out how it's done.
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Oct 21, 2011
we have 3 classes:Class S, class A, class B / A and B inherits S.A has a property A1 and B has a property B1.we also have a collection of objects that has A and B objects.ex.
Dim c as Collection = new Collection
c.add(new A)
c.add(new B)
Now we want to make a general object that will read from the collection.
ex .
Dim obj as S
how can we cast obj in order to see properties A1 or B1 according to the class;
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Apr 19, 2012
I've got a form with a listbox on it.In a second form I inherit the complete first form. But when I try to use that listbox in the second form with e.g.Index = LstWoodshop.FindString (Order(0))(where LstWoodshop is that inherited Listbox) I get the error message:'LstWood shop' is not declared. It may be inaccessible due to its protection level.What or where can I change this setting so that this listbox on form 1 is also available/accessible on form 2?
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Apr 24, 2012
I am writing a database using OOP, i have created my classes ect and i am able to input data.
I have four textboxs, and two listbox's. The first listbox lists all the categories which i have managed to do. Now when the user selects a catelgory a list of objects under that category are listed in the second listbox which the user then selects to display any related data and this is the problem i am having.
[URL]
Code:
Public Class BaseClass
' ScrName is the name of the script file.
Public Property ScrName() As String
[Code]....
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Aug 18, 2011
I am developing one vb application. In that I have one list box. I want to add different types of Items. Like Different Colored and differently aligned text(Like one item item is right aligned and one more is left aligned). Can you please tell me how can i do the same.
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Feb 19, 2010
So I want to click on different things in a listbox and somethings have a picture and some dont. I want the things without a picture to all show the same thing. I've tried this:
Code:
If ListBox1.SelectedItem = object1 Then
PictureBox1.ImageLocation = object1picture
Else
[CODE]...
This only works for object2 and I know why, but I dont know the correct way to make it work for multiple objects.
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Feb 17, 2010
I'm wondering how I can save all my listbox items to a file and load them? Each object in the listbox is a custom class and they are loaded into the listbox kinda like this[code]...
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Jan 6, 2012
I have a function called Modify. It is delcared like so:Public Function Modify(Of SIMType As {New, DAOBase})(ByVal obj As DAOBase) As Boolean
You can see that this function is generic. It takes as a paramer a object that is a DAOBase or subclasses of DAOBase.Inside the modify function there is a call like so:
DAOToGP(obj)This is where the polymorphism comes into play. There are four or so subclasses I have created of DAOBase. I have written a DAOToGP() for each of these types. So in the Modify() function, when it calls the DAOToGP(obj), polymorphism should kick in and it should call the correct implementation of DAOToGP() depending on the type that I pass into Modify().
However, I get the following error:Error 20 Overload resolution failed because no accessible 'DAOToGP' can be called without a narrowing conversion:'Public Shared Function DAOToGP(distributor As Distributors) As Microsoft.Dynamics.GP.Vendor': Argument matching parameter 'distributor' narrows from 'SierraLib.DAOBase' to 'IMS.Distributors'.'Public Shared Function DAOToGP(product As Products) As Microsoft.Dynamics.GP.SalesItem': Argument matching parameter 'product' narrows from 'SierraLib.DAOBase' to 'IMS.Products'. C:Usersdvargo.SIERRAWOWIRESDocumentsVisual Studio 2010ProjectsSIMDev_2SIMIMSDVSIMLibGPGPSIMRunnerRunnersRunnerBase.vb 66 39 IMS
I am kind of at a loss here. I am not sure why it cant figure out which function to call.
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May 15, 2009
Okay this is a bit of a noobish question, but I ran across this today and it somewhat puzzles me WHY it would be this way.
Consider the following structure
Public Class Employee
Implements IPerson
Private _MyManager As Manager
[Code].....
Here is my question: I am wanting to have every person implement the IPerson interface, whether they are an employee, boss, or manager. However, they each have an attribute that refers to their leader (employees have a manager, managers have a boss, etc). Each implementation of their leader could be potentially differnt other than they fact that they implement the IAuthorityFigure interface. I am wanting to have the IPerson interface have a property for the IAuthorityFigure, but it throws a compiler error for me when I implement this b/c the IAuthorityFigure is not the same type as Boss or Manager (even though they implement the interface).
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Oct 29, 2011
i have assignment which using polymorphism to get answer. Below here is answer from the question.anyone give me a code using polymorphism to get this answer
i= 100, j= 200, k= 300
value for i =100
value for(i+j)/2= 150
value for(i+j+k)/3 =200
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May 20, 2011
I have a class that has two methods called "Add." One method excepts a FileInfoA object and the other excepts a DirectoryInfoA objectSo in my code, I'm adding FIAs and DIAs to property lists. But, it throws an exception because it's trying to process a FIA as a DIA, which means that the FIA is being added to the group of DIAs.I commented out the adding of DIAs to see if it would work and it did. When the DIA is commented out, the FIAs are filtered properly and the code executes properly.This is how my methods are declared:
VB.NET
''' <summary> ''' Adds a DirectoryInfoA class and adds it to one of the appropriate list. ''' </summary> ''' <param name="di">DirectoryInfo</param> '''
[code]....
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Oct 5, 2009
I have a problem with access database in my vb project. I would like to fill the listbox with objects from my database. I've attached two images. In first image when i'm using command objDataAdapter.Fill(mydataset....) i can select table property(zaposlen). But in second image or in my second app i dont have an option to select table property in my dataset(there is nothing to select). If i select DataTableDataTable i get next error: DataTableDataTable' is a type in 'WindowsApplication1.baza_podatkovDataSet' and cannot be used as an expression.
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Nov 17, 2009
I have a couple of small classes to represent parts in a search filter. If the searched value equals NonValue the filter is supposed to do nothing. This is defined in a Base Class:
Private Class BaseFilter
Protected NonValue As Object
Protected sQueryStringBase As String = "AND {0} {1} {2} "[code]......
When I then create a StringFilter and check for allowed value:
Dim stf As New StringFilter()
stf.CheckNonValue(MyString)
I get a NullReferenceException (NonValue = Nothing) , when I expected the NonValue object to be String.Empty. Is this a bug in my code, or am I trying to achieve polymorphism in a wrong way?
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Jun 25, 2010
vs2010 vb.net WPF project
This is an experiment to learn something.
I have a class called logitem
it has a datetime property, and a message as string property
I have declared myLogEntries as List(of logItem)
I have a ListBox.
Ok now what?
I have searched but i am getting lost in all the examples.
I have set the ItemsSource=myLogEntries
I think i need a datatemplate or maybe to specify binding source.
I am doing all this in the wpf form loaded event.
I guess i need a sample code for binding a list of collection to a listbox.
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Mar 24, 2011
Suppose I have an interface IFoo with implementation classes VideoFoo, AudioFoo, and TextFoo. Suppose further that I cannot modify any of that code. Suppose that I would then like to write a function that acts differently based on the runtime type of IFoo, such as
[Code]...
Then I have to do my "If TypeOf ... Is" again. How can I refactor this to take advantage of the polymorphism of the implementations of IFoo without manually checking the types? (in VB.NET, though my question applies to C# too)
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Sep 16, 2011
In VB.NET, say I have a function Public Function Foo(ByVal currentShape as Shape) Instead up passing in a Shape object, I pass in a subclass of Shape called Square like such: Dim square As Square = new Square() Foo(square). Do I need to convert my Square object to a Shape object before passing it in? If so, how do I do this?
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Jan 29, 2010
In a program I am writing (in VB.NET, 2008), I have 2 classes, "Receipt" and "Group", each with similar properties, both implementing a custom interface entitled "IIDUser". In my program, I have a number of lists of "Receipt" and "Group", declared like:Friend receipts as List(Of Receipt)
I have written a few functions that apply equally to managing both lists of receipts and groups, declared like this one:Friend Function getNextAvailableUserLabel(ByRef theList As IList(Of IIDUser), ByVal startLabel As Short) As Short
Then called like this:getNextAvailableUserLabel(receipts, s)
I did all this in an attempt for interface-based polymorphism, as I thought writing 2 identical functions (except for that one would be for lists of receipts while the other for lists of groups) would be bad practice (and waste time). However, I get an "InvalidCastException" during runtime. It is explained, "Unable to cast object of type 'System.Collections.Generic.List`1[Receipt_Sorter_v2.Receipt]' to
[Code]...
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Dec 5, 2011
make objects from the ToolBox using code instead of changing existing objects invisible then visible later?
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Jun 23, 2012
I am getting this error, Not sure why it is happening "Error The SqlParameterCollection only accepts non-null SqlParameter type objects, not Int32 objects."I have tried with all sorts of possibilties, now try to enter default data as dummy data,
Using connection As New SqlConnection
connection.ConnectionString = ConfigurationManager.ConnectionStrings("DentalDeviceConnectionString").ConnectionString
connection.Open()[code].....
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Jan 29, 2011
I have a program like this.
Module Module1
Public Class Mstr
Public Property Prop1 As String
Public Property Prop2 As String[code]....
But it is not working as I expect it to. You can see it from.The DtlsB properties of all three DtlsA objects are having values from last iteration.
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Jan 6, 2011
I want to let the user input objects to a richtextbox 1 object on each line, and somehow use Random.Next to select pseudorandomly a few objects, the number 'few' inputted in a textbox.
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Jan 18, 2012
Private Sub Button1_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button1.Click
Using conn As New SqlConnection("Database=Clinic_Management_System;Data Source=.SQLExpress;Integrated Security=True;AttachDBFilename=|DataDirectory|Clinic Management System.mdf")
Dim cmdRecord As SqlCommand
[code]....
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Feb 7, 2010
I have a user control that inherits the FW ListView and I need to dispose of two objects when the form's disposing of it's objects. Here's what I've concluded already, am I on the right track?
[Code]...
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May 1, 2009
long story short, I have created a ListView type control, using UserControls for the parent control and the ListViewItems. Most the of the control is written and works fine, right up to the point where I tried to replicate the 'Control.SelectedItems(0).Index' property and the 'SelectedIndexChanged' event.
Each child object knows its index value, and could pass this value via the SelectedIndexChanged event (assuming this is how it works in a normal ListView control -- user clicks on an item, and that item fires an event updating the selected index value in the parent object).
How does the child object raise an event in the parent object? I have a feeling this could be done with Delegates, but I'm still learning about their usage.
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Aug 9, 2011
getting the following error Unable to cast object of type 'System.Object[]' to type 'OrderService.webdirect_WebLinesRow[]'. On the line
webdirect(web_companyID, web_locationCode, web_customerNumber, web_orderNumber, web_orderReference, web_orderDate, webLinesArray.ToArray(), o_Company, o_LocationCode, o_CustomerNumber, o_OrderNumber, o_OrderStatus, o_OrdDescrip, webRespArray)
I created the webLinesArray.ToArray() array as such
Dim webLinesArray As New ArrayList()
Am I missing an additional cast or something ?
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Aug 28, 2008
I want to compare two objects to check if all the properites of both the object have same value or not. for this i need to use the reflection to enumarate through all the properties of an object and check the value of the property. To try the code just i have written a Employee Class having Two Properties EmployeeNo and EmployeeName. I am creating an object of the Employee class and need to write a function that can list the values of all the properties in the class.
[Code]...
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Apr 22, 2012
i am just trying to apply inheritance ..Below is my Code ... on which i am not getting the output on my Text_Box ... when in write it in a Child Class
Imports System
Imports System.Windows
Imports System.Windows.Forms
[code]....
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Jul 14, 2011
Has someone a hint what I'm doing wrong in VB.Net?
Module Module1
Interface ISearch(Of T As ISearchResult)
Function ids() As List(Of T)
End Interface
[CODE]...
The third cast isn't working. Why? did I miss a oop lesson?
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