.Net OOP Superclass Base.net And Constructor Parameters?
Mar 13, 2009
I have a base class that contains a fairly large number of parameters in it's New constructor. I have 7 subclasses that inherit the Super base class. My question/issue is, all of the subclasses use the same values for most of the parameters in the New constructor of the base class and these subclasses can be called one after the other. I would like to populate the common values for the superclass and then use those for each of the subclasses, but I can't come up with a good way to do this. If I could figure out how to do this, I wouldn't have to pass all of those parameters in the MyBase.New call for each subclass. I'll try to illustrate with some code .
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Mar 15, 2010
In the inherited class I use the base constructor, but I can't use the class's members calling this base constructor. In this example I have a PicturedLabel that knows its own color and has an image. A TypedLabel : PictureLabel knows its type but uses the base color.
The (base) image that uses TypedLabel should be colored with the (base)color, however, I can't obtain this color
Error: Keyword 'this' is not available in the current context`
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Nov 26, 2010
How do I get using reflection the most generic type from a shared constructor in the base class :
Public Class Foo()
Shared Sub New()
'Here we have code to get the type[code]....
I expect the result to be Bar type and not the Foo. Is it possible?
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Mar 3, 2011
comparing C# code and VB.NET and the results between the seemingly identical code were entirely different.(Why C# is always winning over VB.NET?)The explanation given is that C# will initialize the class fields, then call the base constructor, but VB.NET does the exact opposite. Is there a technical reason for the languages to be different? At first glance, it seems that either approach is equally valid, but I can't fathom why they wouldn't have selected the SAME approach.
EDIT: As 'Jeffrey L Whitledge' has pointed out, VB6 did not have inheritance, so I don't think we can say 'to keep VB.NET and VB6 more closely related'.
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Jun 29, 2010
Why VB.NET (vs C#) does not "inherit" the constructors with parameters?
Public Class StopLine
Inherits Microsoft.VisualBasic.PowerPacks.LineShape
Public Sub New()
MyBase.New()
[code]....
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Jun 23, 2011
I searched quickly and not find an explicit answer at the following question:Why VB.NET (vs C#) does not "inherit" the constructors with parameters?
Public Class StopLine
Inherits Microsoft.VisualBasic.PowerPacks.LineShape
Public Sub New()
[code].....
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Jun 1, 2010
I am stuck with a problem about generic classes. I am confused how I call the constructor with parameters. [Code] I get error in the starred area of the DBLayer Object. What might be the possible reason? what can I do to fix it? I even want to add New(byval someval as datatype) in IDBObject interface for overloading construction. but it also gives an error? how can i do it? [Code]
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Apr 25, 2009
In the code below I recieve the compile error "Error Too many arguments to 'Public Sub New()'" on the "Dim TestChild As ChildClass = New ChildClass("c")". I do not recieve it on "TestChild.Method1()" even though they are both on the base class I am inheriting from.
Public Class BaseClass
Public ReadOnly Text As String
Public Sub New(ByVal SetText As String)[code].....
As suggested below but I do not have to do that for Method 1 or other inherited methods and I am looking for the cleanest code possible. This may be a limitation in the system with inheriting parameterized New statements but I can not find it documented anywhere. If it is required then I would like to see the documentation.
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Jan 5, 2011
After debugging a particularly tricky issue in VB.NET involving the order in which instance variables are initialized, I discovered that there is a breaking discrepancy between the behavior that I expected from C# and the actual behavior in VB.NET.Nota bene: This question concerns a slight discrepancy in the behaviors of VB.NET and C#. If you're a language bigot that is unable to provide an answer other than "that's why you should use C#, noob", there is nothing for you to see here; kindly move along.Specifically, I expected the behavior outlined by the C# Language Specification (emphasis added):
When an instance constructor has no constructor initializer, or it has a constructor initializer of the form base(...), that constructor implicitly performs the initializations specified by the variable-initializers of the instance fields declared in its class. This corresponds to a sequence of assignments that are executed immediately upon entry to the constructor and before the implicit invocation of the direct base class constructor. The variable initializers are executed in the textual order in which they appear in the class declaration.
Contrast that with the portion of the VB.NET Language Specification concerning Instance Constructors, which says (emphasis added): When a constructor's first statement is of the form MyBase.New(...), the constructor implicitly performs the initializations specified by the variable initializers of the instance variables declared in the type. This corresponds to a sequence of assignments that are executed immediately after invoking the direct base type constructor. Such ordering ensures that all base instance variables are initialized by their variable initializers before any statements that have access to the instance are executed.
The discrepancy here is immediately obvious. C# initializes class-level variables before calling the base constructor. VB.NET does exactly the reverse, apparently preferring to call the base constructor before setting the values of instance fields.If you want to see some code, this related question provides a more concrete example of the divergent behavior. Unfortunately, it does not provide any hints as to how one might coerce VB.NET into following the model established by C#.
I'm less interested in why the designers of the two languages chose such divergent approaches than I am in possible workarounds for the problem. Ultimately, my question is as follows: Is there any way that I can write or structure my code in VB.NET to force instance variables to be initialized before the base type's constructor is called, as is the standard behavior in C#?
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Oct 13, 2010
In java the constructor is as follows
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can i make 4 constructors with diffrent parameters. now in vb how can i write constructor with parameters.
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Oct 1, 2008
I've been creating short test apps repeatedly to try to understand some of the concepts in VB.NET.For the most part it has been illuminating.I read Bucky's .NET knowlegebase tutorial on passing objects as parameters to newly created forms. He shows how to create a new class that inherits from the base form class and define a New() method with parameters Extending the concept I thought about doing the same thing with a form that was created at design-time (In this case Form2).
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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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Mar 30, 2010
1) VB Allows non-type template parameters2) VB supports explicit specialization 3) VB allows the type parameters to be used as the base class for the generic type4) VB allows a generic type parameter itself to to be a generic 5) VB enforces that all codes are valid for all types of parametrs
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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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Aug 14, 2009
I have a superclass NetworkTest and 3 derived classes PingTest, Pop3Test, SMTPTest. I want to create a big list of all the tests, like this:
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Dec 19, 2009
I have 2 business classes, user & salutation and 2 DAL classes of the same name.
The business classes both have properties of the data class E.g.
Public Property Data() As Data.Salutation
Get
Return _Data
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To access some data, you would do Business.Salutation.Data.SalutationID
Both busines classes inherit from BaseClass which contains all my database access methods.
Is there a way that I can access the Data property of the inheriting classes from the BaseClass?
I assume I will need to use reflection as the property types will always be different.
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Jun 3, 2011
I am getting following error when I am trying to use Convert.FromBase64String "The input is not a valid Base-64 string as it contains a non-base 64 character, more than two padding characters, or a non-white space character among the padding characters."
Dim payloadBytes = Convert.FromBase64String(payloadBase64)
Basically when my facebook registration form [URL]mphone field has a dash in it and encoded string is posted to other page and I am trying to decode it there which creates this error. Basically I am trying to extract data from Facebook Signed Request.
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Sep 6, 2010
I can quickly knock together soem code to xlate base 10 to/from bae 13, but I just wondered if something very easy already exists in VB.NET (or even somethign generic, with base N, but right now I am only looking at base 13)
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Sep 6, 2010
I am attempting to inherit an ASP.NET RegularExpressionValidator and add some functionality to it. I inherited the control and added my custom properties. However, I would also like the client-side functionality to call a different JavaScript function.
In order to do that, I will need to supress what is happening in the AddAttributesToRender method because the name of the function is hard-coded there. Here is what comes up in Reflector for the AddAttributesToRender function in RegularExpressionValidator:
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Note: I tried to add the expando property before the parent class does to see if the code would check for its existence and skip it, but that just causes an exception.
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Sep 13, 2010
Sorry if the title isn't very clear. This is a VB.NET (2010) question I have a superclass called "Device" which has a number of subclasses that inherit it. Some of those subclasses also have subclasses. In particular, I have a class called "TwinCatIntegerDevice" which inherits "TwinCatDevice" which inherits "Device."The relevant parts of Device look like this:
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May 13, 2011
I'm writing a query to select all records that has any part of parameter. I have one table called Employees. Some people have name like this: John David Clark If the parameter is
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I should be able to get result back as long as there's a match in the parameters. If I use Function Contains (q.FirstName & " " & q.LastName).Contains(employeeName), I will not get any result back if employeeName is "John Clark" Function Contains looks only for next words from left to right. It doesn't match a single word at a time. So that's why I used this in the Linq to SQL:
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Aug 30, 2010
I am getting error [07002] the # binded parameters < the # of parameters makers, i checked both parameters were perfect even though i am getting this error here is my code
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Jul 22, 2009
Specifically I have fractal hour... in base 100... that does not reflect what the true minutes/seconds left that it represents
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Feb 6, 2012
Basically Commands has Parameters and parameters has functions like Add, AddWithValue, and etc. In all tutorials i've seen, i usually noticed that they are using Add instead of AddWithValue.
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since it saves my coding time. So which is better to use? Which is safe to use? Does it improves performance?
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Aug 6, 2011
is there a way to get the GET parameters and POST parameters in just one function or Collection in ASP.NET? Like using $_REQUEST in PHP? I'm using VB.NET.
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Jan 31, 2012
I'm retrieving data from Excel and would like to keep my arrays 0 based but Excel returns 1 base. Is there a fairly simple way to return change the array from 1 to 0 base? Or do I just need to create a loop? Here's an example code right here:
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Dec 16, 2009
If Class X is within the scope of Class Y, is X a subclass of Y?If Class A is a sub Class of B, then is Class B considered a super class of A?if Class C inherits Class D is Class D a superclass or parent of Class C?if Class E extends Class F then we can consider Class E a child of F?if Class G inherits Class H and is within the scope of Class I then who is the parent of Class G? Classes that inherits Class J and classes that are within Class J are all sub classes of Class J?
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Jul 22, 2009
When is it run? Does it run for each object to which I apply it, or just once? Can it do anything, or its actions are restricted?
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Apr 1, 2010
A project has a class (CAR Class) with the folloiwng details and the CARADMIN cLASS with the following details: The cardAdmin class has 2 constructor Public Sub New() & Public Sub New(ByVal rec As Rectangle) I dont know how to code the latter constructor..
cAR Class has this method/properties:
Public Class Car
Inherits HVSprite
Private fSoundFile As String
[code].....
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Jun 27, 2009
I have a defualt constructor that has a object of a Database connectivity class:[code]therefore in theory i have to call the defualt constructor of Question from overloaded constructor. [code]How every in realitty is it possible to call the defautl constructor from the overloaded constructor
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