Count Different Objects In A List That All Share The Same Interface?
May 26, 2011
I have an object (MyObj) that itself will hold a List of other objects of various types and I want to count them as they are added to MyObj.That's the simple explanation, anyways...I have an Interface (MyInterface) that all sub-objects agree to. MyObj has a List(Of MyInterface) property that all the sub-objects are added to. MyInterface will expose a property that lets me figure out what subtype each object is (the sub-objects do not inherit from MyObj at all).
But I want to count these sub-objects as they are added to the list, and I'm trying to find a good way to do it. I don't need to worry about decrementing the count, as I am going to mimic the behavior of String and just create a new instance of MyObj if it ever changes, so all my counts will start from 0. This'll hit the garbage collector a bit, but I think this will allow for simpler (and safer) code. The only sane way I can think of to count objects is a very large structure in MyObj that uses bytes to hold the count (I will never have more than 255 of any given sub-object in the list in MyObj). But, even using bytes, this structure will be about 100-200 bytes big in memory (I have that many sub-objects), and I anticipate having a fair amount of MyObj copies running around, too.
I'll also need a large Select Case to know which count property to increment when a new sub-object is added. This seems to be a bit ugly, though I've used this approach several times already.What I am wondering is, instead of counting each object as it is added to the list, is there some way to query the list and count only the objects of a specific type? I wouldn't need to store this anywhere, since it would be dynamic, like querying a database and asking for a count of a specific column or type of record.I suspect Linq can do this, but Linq is also quite slow. Are there other approaches? Perhaps a predicate of some kind?VB (I am not a C# guy):
From i in MyObj.MyList Group i by i.GetType into g Let c as Int32 = g.Count() And that's it so far. I am still googling, but I am getting way too many C# and SQL references.
I have started using BindingList(Of T) for my generic collections whenever I need the objects to interface with the GUI instead of List(Of T). This has worked well for me so far but a few of my collections are stored in Dictionary(Of TKey, TValue) and there doesn't appear to be a corresponding BindingDictionary(Of T).
Has anyone else come across the necessity to use this, and how did they achieve it? Should I implement this myself? (How?) or is there a better solution already available?
I am new to .Net Programming and would like to know if Reflection is suitable for traversing an Object to discover Collections within an instance of a class. I am working with the Microsoft.SqlServer.Management.Smo Namespace.
The plan is to connect to a database, determine what collections exists, then for each of those collections, if the Collection exposes objects which implement the IScriptable Interface, generate a script for the object.How do i do the following (This is pseudo-code as I am seeking assistance with using reflection or some other method to do the following)
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I would like to enumerate all objects in db with one function if possible
I am having trouble following some of the examples at MSDN for LINQ.Basically I have a List Of MyObject. MyObject has a property called Value which is an integer.I want to group all the MyObjects together that share the same Value and then return that Value where the count of the group is greater than 5.I have tried the following,
dim foak = From o as MyObject in MyObjectList _ Group o By o.Value into Count _ WHERE Count > 5 _ Select o.Value
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:
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Private Sub ListBtn_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles ListBtn.Click Dim FS As New FileSystemObject
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I've searched just about every site for some sample code and can only find some C# (I think) code.
i saw jim example in the codebank and i added the percent progress parameter to report progress method (to change the progress bar value)this is jim example:-
vb.net Private Sub BackgroundWorker1_DoWork(ByVal sender As Object, _ ByVal e As DoWorkEventArgs) Handles BackgroundWorker1.DoWork
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I have a small application that consists of multiple forms that each need to have the ability to be updated (not repainted, the data/components values redefined) when called to. So for instance, if I had a form that contained a count of some sort and another form modified that count I would need to update the form that displays the current count. With that being said it needs to implement an interface with these methods (see below). My issue comes when I want to add events to these methods so if I call the UpdateData event it would trigger the OnDataUpdate method, but because of the syntax of implementing methods and handling events you cannot do so.
I would like to create list of child objects from list of parent object. Like If i have list of bookingroom which has one member room then i would like to create list of room from it.
eg. code:
Dim BookingRoomList As List(Of BookingRoom) = New List(Of BookingRoom) Dim RoomList As List(Of Room) = New List(Of Room) BookingRoomList = BookingRooms.FillGrid()
[Code]....
Is there any short cut method instead of iterating over for earch?
All my data objects implement an interface IFillable
Public Interface IFillable Sub Fill(ByVal Datareader As Data.IDataReader) End Interface
In the objects themselves you will typically see something like
Public Class Supplier Implements IFillable
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Now here is the tricky bit. Given that all my property names WILL ALWAYS match my database column names what I want to do is using reflection generate the fill method at compile time and infer the types and column names for the datareader.I am assuming I will need to structure this functionality as some sort of a tool/vs plugin? What I am looking for is guidance on the best way to go about this.
PS: BTW: Obviously I could easily do this using reflection at runtime but I dont want to take the performance hit for it (Although theoretically if I could cache the values somehow (static class?) it might not be too bad).
I need to let the end user move and resize objects (like a textbox or button). There are several examples that demonstrate this in VB, but not in VB Express 2008, based upon VB.net.It looks like earlier you needed to access Windows API, but these calls does not work in VB.net. I understand that these call are replaced by "native" .net calls, but I cannot find any that does the job.
A typial example from old VB is:
Private Declare Function GetWindowLong Lib "user32" Alias "GetWindowLongA" (ByVal hwnd As Long, ByVal nIndex As Long) As Long
I have a class called Tree, it has an arraylist called alTreeNodes. alTreeNodes is an arraylist of TreeNode class. Since I am using ISerializable Interface, I have to provide a specific constructor. I know how to write it for string parameters such as name_value, but how should i do with arraylist of object then? See "???" in the code blog before.
Protected Sub New(ByVal info As SerializationInfo, _ ByVal context As StreamingContext) If info Is Nothing Then
I will get an error message. I tried something like
Code: Public ObjectPoint As PointF Dim cpoint As New PointF() cpoint.ObjectPoint = New PointF(startX, startY) e.Graphics.DrawEllipse(Pens.Blue, cpoint.ObjectPoint, 0.4, 0.4)
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In one thread I'll be adding items to List1(Of Object1), and processing them, and adding the results to List2(Of Object2), however I need to be able from other threads to look at the list and say only give me the items where Integer = (my thread ID), is this possible? Any help, or even links to information that would be relevant to this request would be helpful?
I'm using this code to count up bytes in list box 5. It works but when the value of bytes is 0 i get this {Width 100, height = 200,) I think the problem is the ToString So does anyone know how to count numbers in the list box?
vb Dim total As Integer Dim i As Integer For i = 0 To ListBox5.Items.Count - 1
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I have an operation that will be performed MANY times and so I need it to be as fast as possible, thus I think keeping validations to a minimum is important here.I'm given an image, an offset and a size; and the idea is to take the color that appears the most within the area determined by the size and offset, so far I have this:
Private Shared Function someFunction(image As Bitmap, offset As Point, sampleSize As Size) As Color Dim pixelsColors As New List(Of Color)
I have the following code for Customers and their orders. I want to list all the customerID and the corresponding count of orders. How do I achieve it using LINQ? [code]
