Continuation Of A List (of T) As A Property Of A Class
Apr 2, 2010
This is another continuation of an issue with a List(of T) as a property of a class.Following the excellent advice of AtmaWeapon and others on this forum, I have my classes working fine except for something that is inexplicable to me.I initialize my "course" class at a public level in a module. This is so the data in the class will be available program wide and for the application's lifetime. "Public newCourse As New Course".I initialize a local instantiation of the class TimeTable as newTimeTable [code] This issue is: The List(of T) is populated with data, however, when the loop finishes, what I have is the last set of values repeated "X" number of times in the List instead of the data being different in each element of List( Of T). [code]
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Apr 2, 2010
I'm looking for a tutorial on how to Adding a list(of Class) or Collection as another Class's Property.What I am after is something like the Columns Collection for the DatagridView control.I would like to add Items in the graphics screen. Where the item list is displayed in the left panel and the selected Item properties are displayed in the right panel.
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Oct 19, 2010
I have a base class (ex: Class1) containing a list of another base class (ex: ClassA). Each child class of first base class (ex: Class1AA, Class1AB,..) containing a list of child class of second base class (ex: ClassAA, ClassAB,...)The client must never know which child class is using, then i don't think i can use generic for my bases classes.I try something like this and many more, but i always received errors..Imports System.Collections.Generic
[code]...
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Oct 14, 2009
Stack Overflowers:I have been racking my brain trying to get an List(of T) type array to be the property of a class. I know there has to be a simple way of doing it and I can't find a good example on google. Everytime I create a class that I think will work I get the "Object reference not set to an instance of an object" error when I try to use it. My thinking now is that I cannot use it in the way I was hoping to. Here is my latest attempt:
Public Class Item
Private _itemno As String
Public Property ItemNo() As String
Get
[code]....
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Oct 8, 2010
I have a class called Questions. This Questions has properties QuestionID and QuestionAnswer. My list of Questions has QuestionID like 2, 3,4, 15, 12, 24,22,,,, etc.I need to sort this List of Questions Object based on QuestionID and store in another Questions object.
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Oct 4, 2011
I have the following class:
[Code]...
I could be way off here, but it almost seems like ID.IDlist points to the address of mylist and so when mylist is cleared so is ID.Idlist. It seems as though the reason the second block of code works is because I am creating a new list in memory for each ID object and ID.IDlist just points to it... is that right?
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Mar 12, 2011
I have a file name that is found at multiple paths. I want to present this data to the user in the format of a DGV. I have a DGV with one text box column for the name, and another combobox column for the paths. I am having trouble getting the combobox column to bind to the property of the class that returns the paths.
[Code]...
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Nov 29, 2011
Is it possible to create a user control with a list of custom class type property? If it is, how can I? The issue is that, in designer mode the property is not displayed in property window. I can add the list on markup but when i switch to the designer mode it gives an error which is 'The user control does not have a public property named BookList'.
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Oct 20, 2010
In my application I have a class called "RCategory" as illustrated here:
Public Class RCategory
Public Property RCatNum As Integer
Public Property RAct As Char
[code]....
I'm trying to add to my list using the following code:
For ct As Integer = 1 To 8
Dim c As New RCategory With {.RCatNum = ct,
.RAct = dr("RACT" & ct.ToString).ToString,
[code]....
I'm getting an error when I get to the bottom line, though...when I actually execute the RCat.Add(c),I get a System.NullReferenceException was unhandled by user code Message=Object reference not set to an instance of an object. What must I do to be able to use a List (of T) in my class?
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Jun 1, 2012
I have a very simple class that holds a few public properties - ID, Text, Colour, etc. and a Boolean called 'SelectedItem'. Just like the Checked property on RadioButtons, only one item can have its SelectedItem property set to True within a particular group. Note: there will be several separate groups (lists), each allowed to have only one item with SelectedItem = True.
My first thought was that I would probably just have to handle everything outside of the class, setting SelectedItem to False for every other item in a particular list when another item was selected. But that seems rather inelegant to me. So I've been trying to think of how this might be done within the class. For example: could I perhaps have a private string property called say "GroupName" - set in the New sub when adding a new instance of the class - and then use a private shared method to set every item's SelectedItem property to False, provided the item has the same GroupName as the newly selected item? I would have a go at doing this but I have no idea how to enumerate every instance of a class from within that class, or whether that's even possible. Is it? Or is there another (better) way to achieve my goal? Here is a cut-down version of what I've got so far:
Public Class ResourceItem
Public ID As Integer
Public Text As String[code]....
As can be seen: instead of instantiating a new ResourceItem and passing that as an argument to the manager's Add procedure, I'm simply passing the details of the new item and the procedure is creating the item from those. I don't know whether this is a good or bad idea - please advise - but I've done it because I couldn't figure out how to make the SelectedItem property only writeable by the manager, so I wanted to avoid having directly accessible objects that could have their SelectedItem property set to True without it deselecting all the other items in the same group. Of course that still leaves the possibility of setting a variable to one of the manager's list items and setting it from there, so I would still like to know how I could prevent that, if possible.
UPDATE: I didn't use the code above in the end, deciding instead to go with Cyborgx37's solution - which seems to work perfectly well for me despite the warnings about best practice. I also realised I would need to use the same class in another scenario where multiple items could be selected, so it was easy to add a Boolean property to the manager to enable that.
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Feb 21, 2011
I have the following property in a property grid in VB.Net 2010.
<Description("Rapid Entry Post Car Wash Settings CarWashOptionPushButtons"), _
Category("Post Car Wash")> _
Public Property CarWashOptionPushButtons() As String
[code]....
I need to make this property a list box that gets the values from a database table and populates the list box with the values from the table. I have tried numerous things to no avail.
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Aug 13, 2009
I have the following code:
Public Class MyColorsClass
'Constructors
Public Sub New()
'Empty Constructor
[code]....
However, if the empty constructor was called to instatiate this class then the colortype is not yet set. Therefore, if one accesses the 'IsColorCool' property it will always return 'False'. Now for the sake of this example, I must keep the empty constructor as part of the class.Now I could add some code in the 'IsPropertyCool' to check and see if a ColorType has been defined, and throw an exception if it has not been set, but I don't really want to do that.I also could always move the logic OUT of the property and into a method on the class called 'DefineIfColorIsCool' or something, and make the owness on the caller to make sure the method was called if they want to use the property 'IsColorCool'?
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Apr 7, 2011
Supose a base class
Public Class airplane
Private var_num_seats As Integer
Private var_num_engines As Integer
[code]....
Obviously, I don't wish that the class Glider has the method "start_engines" neither the property "num_engines". Otherwise, other child classes may have. How can I supress these property and method in child class, not just ignoring (if I can)?
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Sep 29, 2011
I have procedure (Import) that calls a for a new instance of frmImportData. I also have a class name clsBatch that has a data table property called prpParametersTable.For some reason, I get an error (indicated below with ERROR>>>) when trying to assign prpParameterTable to cv_dtImport2. The error states "Object reference not set to an instance of an object.". Why does this error not happen when I assign dtBP to cv_dtImport1? Both cv_dtImport1 and cv_dtImport2 are equal to Nothing and in my Import procedure dtBP = prpParametersTable.
Public Sub Import(ByVal clsB As clsBatch)
Try
Me.cv_clsB = clsB
[code]....
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Nov 14, 2009
I have three class files, accounts.vb and transactions.vb in addition to my form.vb. I am unable to retrieve a member variable from on class from inside the other. When the combobox index changes, the program loads the correct account (checking or saving) from two different sequential files. I don't think I have the calcBalance procedure in the correct class file. And that is what I am having trouble with. Accessing it to display it. [Code]
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Mar 30, 2010
This is a bit of a continuation from a previous post for which AtmaWeapon was very informative.
Problem:
A parent class has a sub class with various properties. A property of the parent class is a List(of T) with T = the sub class The issue is how to store data in the sub class of the instantiated parent
Some example code (hopefully formatted correctly):
Code:
'=========== Class Definitions =============
Public Class courseClass
Public Class timeTableClass
[Code].....
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Oct 1, 2009
I'm looping all the properties in an object via reflection:
For Each p As PropertyInfo In values.[GetType]().GetProperties()
If p.CanRead Then
'Do stuff
End If
Next
how to determine whether the property in question is a generic List(Of T)? If it is I need to loop the list itself.
I've experimented with GetType and TypeOf but have not managed to get anything working.
To clarify, I want to keep this generic. I do not want to specify the type of T, I need to loop the list items and call the ToString method on each item. T could be one of a number of different types (application specific reference types). Is it possible to do this without specifying types?
(VB.NET 2005 with .Net 2.0)
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Apr 7, 2012
I have a class that has the following property that is generated by the methods in the constructor.
Public Class clsLoadTables
Private _ds As New DataSet
Public Property ds() As DataSet
Get
[CODE]........................
My problem is that I do not want to inherit this class, but I have other classes that need to access the ds DataSet property. If at all possible I would like to not use inheritance and not load my datatable more than once in the program.
Here is my failed attempt to access the property inside another class that is not inheriting clsLoadTables:
[CODE].........................
How I can access this dataset that I want to load only once in the program from many classes without using class inheritance or a global module?
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Jul 29, 2010
I know that an interface can contain another interface within it.But;can a class contain another class within it?Can an interface contain another interface within it?
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Jan 11, 2011
I have a List myList of MyObjects. Is it possible to check if myList contains a particular myObject based on a property of myObject in VB.NET? In C#, you'd something similar to this right:
myList.Exists(myObject => myObject.property1 == 3)
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Apr 27, 2011
I want to read a number of items from a file and then associate each of those items with a new button at run-time, so that when the user clicks one of the buttons I can display some information about that item.Can I use a LIST to manage these buttons and items? Can I create a new class and have each list item of that class, such as 'btnID', 'btnText', etc... ?
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Jun 21, 2010
I am trying to create an list or an array of a class.Here is my "Ingredient" class that I am trying to create a list of:[code]In my "recipe" class, I am want to create a list (or array) and I am drawing a big blank on how to do it. Can anyone point me in the right direction?
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Jul 28, 2010
I have two classes, and for a property in one of the classes I'd like to be able to load it up with an array of the other class. However my attempt at accomplishing this results in a "Object reference not set to an instance of an object" error. I know it's a rookie mistake, but I'm stumpedssist?
My code is as follows:
Namespace Parking
Public Class garage
[code]......
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Mar 23, 2011
Public Class notifierMain
Public Class Contacts
Inherits List(Of row)
Public Sub New()
[code]....
When I debug this winforms application I get curType = "notifier.notifierMain+Contacts+row" I want to the Validate function to know it is in MyContacts. How do I do this?
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Nov 5, 2011
I wish to make a project where a teacher views a list box with a list of students of a class. When he selects a name from the first list box the second listbox would change its data to show the grades for that one student.
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Jan 27, 2011
I'm getting System.NullReferenceException error when I try to add the employee info to the Employees list.
[Code]...
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Jul 5, 2010
bare with me during this silly example. :-) Let's say I have a class like this:
Public Class Animal
Public iLegs as int32 ' Number of legs
Public bWings as Boolean ' Wings? Yes/No
End Class
And another class that inherits the "Animal" class and adds one more property:
Public Class ScaryAnimal
Inherits Animal
Public iScariness as int32 ' 0-100, how scary is it?
End Class
Now, if I have an instance of "Animal" with some values in it, and I decide I want to cast it to a ScaryAnimal for some reason, how do I do that without having to create a new instance of "ScaryAnimal" and copy each property value?Basically I'm looking for a way to do this, without having to write the lines marked with '*** below:
[Code]...
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May 26, 2012
y have this class
Private Class MyClass
Public Property propertyOne() as String
Public Property propertyTwo() as String
[code].....
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Jan 6, 2011
I have a long line of text to write to the console so I end up with the following code. Mind you, the IDE (VB 2010 Express) error list gives no error when the code is like this, it even build without error. However when the console runs the debugger gives me an exeption error.
[Code]...
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Mar 6, 2012
I am trying to understand classes in VB 2010. I am a bit confused with displaying information from a list into a listbox.When I run the following code, the word collection appears in my list box. How do I drill down into 'hostnames' to display the info I want.
Public Class computer
Private _HostName As String
Public Property HostName As String
[CODE]...
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