VS 2010 How To Eliminate Default Constructor
Jan 19, 2011
I have written a number of classes in my time in VB.NET which set the basic elements in a custom New constructor through parameters. This makes things easier and enforces discipline. However, using Public Sub New() becomes pointless. If someone else tried to use this class, he or she could make a mess of it all by using Sub New without the arguments. I'd like to remove this method but I haven't found out how. I could make it raise an exception, but that somehow seems unseemly. I'd like a neater way. Does anyone know how?
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Dec 27, 2010
I have a base class which must be overriden. This base class sits in one dll shared by all. The derived classes will each be in their own dll such that the addition of a new derived class can be done by distributing a new dll. The set of dlls, and therefore the set of derived classes, will be discovered by the main program on startup. That's all pretty straightforward. The problem is that the main program needs to be able to query a database to figure out which type of derived class it needs, then create a class of that type. Naturally, it can't know which types will be available ahead of time because even I don't know that. The program has to be dynamically extensible.The obvious way to do this is to have an interface in the dll that is implemented by a class with a default constructor. The sole purpose of that class would be to return an object of the type (one of the derived types) defined in that dll. The derived types can't really be this class, because they can't have a default constructor since the base class doesn't have a default constructor, and the derived class can't make up the arguments that the base class constructor needs.
So basically, each dll that houses a derived class would also house a simple class that implemented an interface for the sole purpose of creating that particular derived class. The main program would examine the dll to find a class that implemented the interface, and once it found one, it could ask it what type of class it created, or it could ask it to create an instance of that class. It seems like there ought to be an easier way to dynamically add new classes to the project. It seems like the derived class ought to be able to tell the main project what type it was. This could be done, except that the derived class would have to exist before any of its methods could be called unless the methods were shared. Since you can't have a shared method in an interface, the interface itself would make no sense at that point, in which case I would need to discover whether the class in the dll derived from the base class in the second dll, just to figure out whether or not I wanted to create it. That's getting convoluted by now, so I guess I'll leave it there. The basic point is that the base class is known to the main program from a common dll. The number and types of derived classes can't be known at this time, so the program has to be able to discover them dynamically. Each derived class will sit in its own dll (or there could be more than one in a dll), and has to be discovered, and instances created, as needed, by the main program.
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Mar 4, 2011
One would think I'd already know this, but I never really gave it much thought before now. When declaring a member variable for a class, is it better to set the default value at the declaration
Private m_strMyVariable As String = ""
Or is it better to do it in the constructor
Private m_strMyVariable As String
[Code]....
Should I maybe always specify a value at declaration, even if it's Nothing, and just override that value in the constructor(s) as needed? Or is it situation specific? If so, a really quick rundown of which situations might warrant which treatment would be nice.
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May 25, 2011
I have been getting up to speed with the MVVM pattern in Silverlight and was wondering how to implement binding from the View to the ViewModel when the ViewModel constructor has a parameter if an interface type.If I bind the viewmodel to the view in XAML then you can not use a parameterised constructor. Given that I was creating a default constructor passing an instance to the parameterised constructor but this breaks the abstraction.
View
<navigation:Page x:Class="QSmart.DataViewer.Report.RecentFailures.Report"
xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"
xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"
[code]....
Is it recommended to use the code behind of the view to pass into the parameterised constructor and then bind to the viewmodel?
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Feb 3, 2010
I'm doing a lab for school, and I came across something I have never done before: create a default constructor within my class. It involves creating a private field to store the connection string, then create a default constructor that sets the connection string.
Here is what I have so far:
Public Class Appointments
Private sqlconnection As String = ConfigurationSettings.AppSettings("ConnectionString")
Private Property connectionstring() As String
Get
Return sqlconnection
[Code] .....
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Jan 1, 2011
where can I find the default constructor of a windows form? I mean:
Public Sub New()
End Sub
I should say that I Use Visual Studio 2008 as my editor.
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Mar 16, 2012
I'm trying to create a Wizard at runtime in VB.NET using the WPF NavigationService and I'm having some problems. I need to add controls to the PageFunction pages at runtime which seems to involve passing arguments to the PageFunction pages when I create them (prior to navigating to them). This means that the PageFunction pages need to override the default constructor and add arguments to it. This seems to work fine.
The problem is that I also need to call OnReturn once I've navigated beyond the first page (to go back to a previous page) but the OnReturn doesn't work unless I use the default constructor on the PageFunction page it is navigating back to. The work around I've been considering is creating some global values that the PageFunctions could acssess at runtime in their default constructor but I can't figure out how to define global variables in the MainWindow that the PageFunction pages can get access to.
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Feb 15, 2010
I have an abstract class which requires a delegate to function. I pass the delegate into the constructor. Now that I have a non default constructor I need to call the abstract class's constructors from the concrete class which means that I need to use MyBase.New(...). I have included a quick example below.
Public MustInherit Class BaseClass
Public Delegate Sub WorkMethod()
Private _Work As WorkMethod
[code]....
I have tried to do this but I keep getting the following error: "Implicit reference to object under construction is not valid when calling another constructor".Can I not do what I am trying to do above? I initially had the delegate setup in its own setter method. But then I am creating a deceptive API because it does require a point to a method to work properly.
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Nov 2, 2009
what's the rationale behind this limitation: Constructor call is valid only as the first statement in an instance constructor i want to pass an argument to my constructor which validates this argument and calls mybase.new according to this argument but it doesn't let me
example:
Public Class prob
Inherits System.ApplicationException
Public Sub New(ByVal problem As String, ByRef inner_exception As Exception)
[code]....
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Nov 25, 2011
I have a combobox which contains a sample of names selected from a table.Currently the default name displayed in the box is the 1st name found in the table. What I would like to do is display the name of the person who is doing the selection as the default. The name is stored in a public variable 'PubName' and I do not want the user to be able to type into the combobox themselves.Is this possible?
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Jan 3, 2012
I trying to create application that can read loss bmp with bmp constructor, what I mean loss is bmp without header, here the sample of loss bmp (zip is including with original bmp): Download (you can see the different by comparing the original bmp and loss bmp with hex editor, the different is loss bmp don't have 54 bytes header bmp) Height of image is 126 px and width image is 45 px,how I can preview that loss bmp in picture box? someone of my friend say, its need BMP Constructor to preview bmp properly but he doesn't know the code?
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Jan 25, 2012
I was reading a old post, and came along this post in particular by jmcilhinney... [URL]He states Quote: Originally Posted by jmcilhinney The other alternative is to do your initialisation from the constructor instead of the Laod event handler. My question is...how/where is the constructor? I can't seem to do the right internet search to find out how to do this.
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Aug 15, 2010
I developed an app, tested on few computers and all seemed fine. But now, some people suddenly get an error, which I can't repeat on my computers. Part of the exception:
** Exception Text **
System.TypeInitializationException: The type initializer for 'NumoABC.functionsBurtuSummas' threw an exception. ---> System.InvalidOperationException:
The form referred to itself during construction from a default instance, which led to infinite recursion. Within the Form's constructor refer to the form using 'Me.'
at NumoABC.My.MyProject.MyForms.Create__Instance__[T](T Instance) in 17d14f5c-a337-4978-8281-53493378c1071.vb:line 180
at NumoABC.My.MyProject.MyForms.get_MainForm()
[Code] .....
The If Me.Created = False Then is because while the form is loading, some events fire the updatePersonDataHandlers() sub, but I don't want it to happen until form is fully loaded. In the module functionsBurtuSummas line 2
Module functionsBurtuSummas
Private f As MainForm = MainForm
I have many modules who work with the MainForms' controls, so I use a private variable f to refer to the MainForm.
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Feb 11, 2012
Implementing a simple MVC in vb. The controller instance creates and holds instances of the model and view:
Public Class Controller
Public Property myModel As Model
Public Property myView As View
[code].....
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Jan 27, 2012
I created an even on a form called Sub New so I can handle some events and close the window down if there is an error.Upon doing that, I came across 3 errors that I don't know how to fix.[code] ShowDialog really isn't necessary I could just use .Show. I want to use ShowDialog because the line under those 3 shows the current form.How do I pass the date to the form?In case it's relavent, my code for sub new on frmEmail.[code]
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Jul 19, 2011
I'm trying to create an array to be handled during my code. I want to create it as soon as I open the program so I've placed it in my bit of constructor code. This code was working fine before I tried to initialize a new array in there but when I place that in I get the above error message. This occurs whether I put the new array bit of code first in my constructor class or not.
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May 26, 2012
Is it possible to prevent any row in a grid from being highlighted? I'm familiar with the "SelectionMode" property. I manually add rows to a DGV and the 1st row is always highlighted. I'm trying to prevent this from happening.
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Nov 10, 2007
How to eliminate decimal points in VB.net.what kind of function should i use.
For example, i have number x= 23.13 i only want to show x= 23 and if i have another number x=23.89 i also only want to show x= 23
[code]...
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Feb 29, 2012
Lets say I have a variable: varEmail. It contains a variable equal to the user's email address, so it might contain a value likeNow, lets say I want to get just a portion of the email address, e.g. strip off the domain, like so:
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Jul 15, 2009
I am trying to get the html source of url...I AM USING THE AXWEBBROWSER AS OPPOESED TO THE CONVENTIONAL ONE..I have this code to display a textbox in my Axwebbrowser containing the Page source when the document is completed. Here is the code: [code] The maximum text length of the textbox = 99999999999..When I try to get the document.Tostring, I get this: System.__ComObject..And When I try to get the Html as a htmldocument I get nothing, and when I try just go get the document I get nothing.Does anyone know how I can eliminate this malfunction / error? Can anyone show me a different code to get the html / source of the document of the webbrowser?
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Feb 14, 2012
I have issue is its creating mlitple records of same check number in payment headerfile1 and payment headerfile2 for diffrent invoices.
[Code]...
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Feb 13, 2009
when i run code after 60 sec it display following error what is this error and how to eliminate? ContextSwitchDeadlock was detected Message: The CLR has been unable to transition from COM context 0x2040a8 to COM context 0x204218 for 60 seconds. The thread that owns the destination context/apartment is most likely either doing a non pumping wait or processing a very long running operation without pumping Windows messages. This situation generally has a negative performance impact and may even lead to the application becoming non responsive or memory usage accumulating continually over time. To avoid this problem, all single threaded apartment (STA) threads should use pumping wait primitives (such as CoWaitForMultipleHandles) and routinely pump messages during long running operations.
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Sep 23, 2009
In ASP.Net Web Forms there are cases that I've come across that create order dependent code. As an obvious code smell I'm looking for solutions to solve this problem.
A pseudo-code example would be: Calling Code :: Page.aspx
protected void Page_Load(...) {
var control = LoadControl("ControlX.ascx");
// Ugly since the control's constructor is not used by LoadControl
control.SetDependencies(...);
[Code]...
LoadControl has two signatures, the one used above accepts a string for the control classes physical location and correctly creates the child controls. Whereas the second signature accepts the control class as a class type, and any parameters for the constructor, however the child controls are not created as detailed in TRULY Understanding Dynamic Controls.
So how can I eliminate this order dependency in the cleanest way? My first thought is that if I dynamically created the child controls in ControlX, but then that can be cumbersome for larger controls.
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Nov 25, 2011
So basically I'm making a BINGO game on vb 2008 and i have a "call number" button. The letter and numbers get added to a list box each time. But i do not want the same number to be called. Is there a way that the program can read the items in the list box and not generate (Randomly) the same value again to be displayed in the label.This is what i have:
Callnum = Int(75 * Rnd() + 1)
lstNumbersCalled.Items.Add(lblCallLetter.Text & " " & Callnum)
[code].....
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Feb 24, 2011
I have a Login Form and ...
I have this code to create an account on my disc:
Try
Dim aa As String
Dim ab As String
[Code].....
But now I want creat a button to emilinate accounts, and I dunno how to do that.
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Sep 5, 2010
I have a text box where I only want to be able to enter each character once, so no AA or 99, only one of each character. This is so I can paste into the field, but where any duplicates would be eliminated. I've tried using this code, but am not sure where I go wrong.
[Code]...
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Dec 26, 2011
I'm sure there has to be a simple answer or easy workaround for this, but I can't seem to track one down anywhere that I've looked/asked.So, here is my question:I'm printing some lines of text. I want to lose the footer.
[Code]...
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Jun 7, 2010
Not sure how to do thisI have a hierarchy:
Deals at the top
Deals is a collection of Deal
Deal is a collecton of DealSlots
[code]....
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Aug 14, 2011
I am trying to find a solution, in eliminating repetitive string names, say for ex.,in a literal field, i am populating names of the contributor of certain article's history version, and so, if "ron" has contributed to the versioning of an article 3 times, the name "ron" gets added to this literal control, and outputs "ron" 3 times.
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Feb 17, 2012
Dim regMatch As String
[Code]...
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