Generics - List(Of T) - Use It To Hold Items Of Several Types?
Oct 3, 2009
Assuming a base type of "Message"...
[Code]...
I would like to have one collection of Message objects which can be either PhoneMessages or MailMessages, so that I can iterate through the list and deal with each message based on what type it happens to be.
Attempting just to use .Add() fails, saying that I can't add an item of type PhoneMessage to a List(Of Message). Is there some elegant way to accomplish what I'm trying to do? I had thought I could accomplish this with generics, but I think there's a gap in my understanding. If it can be accomplished in .NET 2.0, that would be ideal.
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Mar 21, 2011
I have been trying to use the Generics List as a means of storing a large amount of data that I am reading in from hardware. I defined a class called 'Datapoint', that has several public variables of type Double, and as I read in a number of points (this is of variable length, and could potentially be very large), for every point I create a new instance of 'Datapoint', update its fields and then add it to a List(of Datapoint) which I named 'Datalist'. All works fine, except when I come to reset the List, I do not know how to free up the allocated memory. I have attached some snippets of code,
[Code]...
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Mar 8, 2012
How can I create a list (of my custom structure) to hold only unique items? This list should be created from another list.[code]...
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May 18, 2009
Is there any way to select items in a list that aren't contained in another? For example:list1 = From t In list1 Where Not list2.Contains(t.column1)That gives me the error:Value of type 'Integer' cannot be converted to '<anonymous type>'which makes sense, since list2.Contains is expecting the same type as list2. However, the list types are different. I want only to select based on column comparisons.
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May 26, 2011
Is this possible in object-oriented design? I'd like to specify that in an inheritance tree, the type of a property in the child classes is different from the type of that property in the parent class. But the types are polymorphic because they derive from the type used in the parent class. e.g.:
[code]....
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Jun 10, 2009
Is it okay for a structure variable to hold a small number of reference types? I thinks it's fine because the pointers themselves are not that big, regardless of what they're pointing to. But I never did fully figure out the whole heap/stack thing, so I'd like to make sure.
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Jun 30, 2009
I'm basically brand new to LINQ. I've seen some examples that allow me to strong type objects using LINQ but I don't really understand them because they're in C#, which I guess lets you do different things with LINQ(I think?). [Code] I just want to get a list of all the products from the XML doc and put them into a Generics list.
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Dec 20, 2010
I know boxing and unboxing part in arraylist but question is if I define only string in arraylist then there is no question of boxing or unboxing. What will be the difference.
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Mar 24, 2009
I am trying to limit the size of my generic list so that after it contains a certain amount of values it wont add any more. I am trying to do this using the Capacity property of the List object but this does not seem to work.
Dim slotDates As New List(Of Date)
slotDates.Capacity = 7
How would people advice limiting the size of a list? I am trying to avoid doing a statement to check the size after an object is added.
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Jul 10, 2009
I have several different lists I want to call. They all have the same format for the class:
id, value, description, order.
Instead of creating a bunch a classes to return the all of the many lists, I wanted to use generics and just tell it what kind of list to return. However, I can not figure out how to populate the classes.
Here are 2 examples of function in my calling code. This should indicate the type of list and the stored proc used to get the data:
Public Function getTheEyeColors()
Dim glEyeColors As New GenericList
Return glEyeColors.GetALList(Of EyeColor)("GetAllEyeColors")
End Function
[Code] .....
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Jun 24, 2009
so the way I have this working now I'M using System.Collections.Generic.List(Of T) for holding 100's of a structure.Dim Users as New List(Of User)
I was wondering if there was any better way or faster list container or something like this in the .net framework?
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Nov 30, 2011
I am a first year coding student and we are starting out with Visual Basic. Up until now I have been able to figure everything out, but I have run hard into a wall and I don't feel like I've been taught how to get over it. Here's the thing.
First Form
Contains a list box for products selected, and four text boxes for Subtotal, Tax, Shipping and Total.
Second & Third Forms
Each contain a list box of books to select from which will be added to the first form.[code]....
I feel like I am doing it wrong right out of the gate - as you can see I am going by the item that the user chooses, and adding a constant value that I have pre-defined in a module. Then I add the name of the book to the first form - but here's the issue.That text string doesn't hold a value.SO, when I use the remove button on the first form - the text string removes but the subtotal, tax, shipping and total boxes do not change in the least bit because the item that I removed doesn't retain any value.
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Aug 3, 2009
Is there a limit to the maximum amount a List(Of T) can hold? I need to know because I have a program that could potentially wind up in a really large loop that would add over 200 or so items to a list at one time.
MSDN search didn't really tell me much, but I'm in a rush at the moment, and was just wondering.
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Jun 9, 2009
I have two objects that are derived from same the base class. ets say ObjA is the base class, and ClassB and ClassC inherits ObjA. f I have a dim lst1 as List(Of ClassB) im list2 as List(Of ClassA)nd and I want to check for the existence of something being in lst1 that it is in list2, now I am only interested in comparing against one key bit of information that it is declared in the base class and is a string. How can I iterate through the lst1 comparing against list2? I thought I could I overload/override the Equals method but I am having no joy for either of the classes and say some thing similar to
Public Overloads Overrides Function Equals(ByVal obj As Object) As Boolean
Dim temp As ClassA = TryCast(obj, ClassA)
If temp.Id = Me.Id Then
[code].....
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Apr 28, 2009
I am using VB.NET (version 2008). I have two types of items populating in a listbox (checked listbox). For example: lets say one is type "A" and other is "Type B". Their names maybe same so if the user sees those items in listbox then he won;t be able to determine their type until he click on them and checks out its properties. I wanted that I add each item to listbox and colour them so that blue for example means type "A" is there and red means the other. So this way I will be able to know at a glance that how many item of what type is present. I guess it may not be possible to do that in a standard checkedlistbox. I am also using component factory's krypton controls which enhance the gui of an application. But I dunno if I can progress using that.
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Jun 8, 2010
I'm writing a program and currently have 4 lists called Palette1, Palette2, Palette3, Palette4.Each contain 15 list items of Color type.I was hoping to create an array of lists but have been unsuccessfull in doing so.[code]
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Jan 20, 2011
If I create a list for a TextBox:
[Code]....
I am able to only add controls that are of type TextBox. My question to you is, can I create a List to hold more than one control type or do I have to create a list for each control type?
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Nov 14, 2009
Is it possible to add Excel Custom Chart Type names to a list box at run time? That is, Microsoft.Office.Interop.Excel.Chart.XLChartType values to a list box?
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Oct 31, 2011
Could any one list the encryption types in Visual Basic.
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Nov 27, 2009
I need a list of all the SQL types and their .NET (vb would be preferred, but C# also works for me)equivalent.
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Jun 23, 2009
I really need to know the list the types of components that are provided by the VB .Net?
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Mar 11, 2009
Any best approach to what I'm trying to achieve (linq to sql, returning list of data to show in a grid/list etc etc)... Its complaining about anonymous type conversion, and from what I'm reading, thats not elegant way of doing it.
Public Function GetHistory(ByVal historyId As Integer) As List(Of ?????????)
Using dc As New myDataContext(Application.GetConnection)
Return (From t In dc.ActionTypes, a In t.MyTable Where a.HistoryID = historyId Select a.ActionOn, a.ActionBy, t.Description, a.ImpactedItem, a.ActionDescription).ToList
End Using
End Function
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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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Mar 16, 2011
This program is supposed to allow the user to check items in a checked list box. If the item is checked, it goes into the Completed List Box on the right. The program then adds the unchecked items to the Pending list box on the left. I keep getting placement values (e.g. O,1,2) instead of the strings (e.g. "Key Returned") in the list box results (see photo attached)
Public Class frmCheckOut
Dim i As Integer
Dim cleaning As String = "Cleaning Inspection"
Dim damage As String = "Damage Repaired"
[code].....
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May 16, 2011
Another program I am working on for fun, I am basically shuffling a list inside a listbox, what I want to do is delete the rest but not sure how to go through with that. At the moment I have this: [code] Just contains the code, declarations outside weren't included.So anyway, once clicked, it will call on the function to basically shuffle in a for loop, I was wondering if I should (or how should) create another function and call it in the click button or have just a loop in the click button so it deletes half the list. What I am doing is I have 20 list of items, I want the program to shuffle the items and then deleting the lower 10, meaning, if I had 10 items and wanted 5 top, I'd want: 0, 1, 2, 3, 4 and deleting 5, 6, 7, 8, 9.
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Jul 20, 2011
I am attempting to read the results from a SQL query into a List(Of) and I can see the List.count while adding items to the List increments, however in another part of my code when I am attempting to read the List the List.Count returns 0. My List is as follows:
[Code]...
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Nov 27, 2009
I have an error panel that is subbed in to a page if an error goes wrong to gracefully handle and display errors.Currently, I am just appending the error messages to a string and pushing that to a label. If you have multiple errors, this gets messy.I'd like to push each error to a list item in a bulleted, unordered list.How can I dynamically generate, from a vb codebehind file, new list items inside of an undordered list element?
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Jan 25, 2011
I have two generic lists, named ListA and ListB. Both ListA and ListB could potentially have duplicate items. What I would like to do is use LINQ to grab the items in ListB that are not in ListA, but I'm unsure how to do so.
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May 5, 2010
i want to search item A (from a list of X items) in list B but i want to get the item not found example Search ITEM A in LIST B if not found then return a print....if found continue with ITEM B..and so on.
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May 23, 2012
That was probably bad title, but I'll illustrate what I'm trying to do. I have a method in a class that I need to call several times. The method returns a List(Of String). I'm just grabbing some information from a database.
VB.NET
Public Function GetTestList() As List(Of String)
Dim int As Integer = 0
[code]....
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