What is the difference between a class with protected constructors and a class marked as MustInherit? (I'm programming in VB.Net but it probably equally applies to c#). The reason I ask is because I have an abstract class that I want to convert the constructors to shared/static methods. (To add some constraints). I can't do this because it's not possible to create an instance in the shared function.
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explain to me the differences between an abstract class and a class marked MustInherit?
Both can implement shared and instance constructors and logic. Both can/must be inherited.
So why use one over the other and what is the difference?
Edit: Sincerely apologize I have got my languages mixed up. Will mark correct answer as soon as I am allowed.
i have 2 mustinherit classes where one is a generic one:
'Visual Basic 2008 - .net 3.5 - Any CPU
Public MustInherit Class BaseObject
End Class
Public MustInherit Class BaseObjectList(Of T As {New, BaseObject})
Inherits List(Of T)
End Class[code]...........
i receive: "Type argument BaseObject is declared 'MustInherit' and does not satisfy the 'New' constraint for the type parameter"users would never enter data in the wrong form,files they choose to open would always exist and code would never have bugs.
Dim box As MultiTextBox = New MultiTextBox
Dim i As Integer
for i = 1 to 3 Step 1
lengthWidthHeight = MultiTextBox.GetItemValues()
Next i
This excerpt of code is using the NXOpen API. In the NXOpen API, the MultiTextBox class is public. However, when I compile the code I get the message:
'NXOpen.UIStyler.MultiTextBox.Protected Sub New(ptr As System.IntPtr)' is not accessible >in this context because it is 'Protected'
My question is, how am I getting an error about protected scope? Could it also be that the API documentation is incorrect?
I've got an Interface that dictates classes that implement it to use a large amount of properties and a few methods. I've been using this interface for some time and I have a large amount of classes that implement it.
Now, I need the interface to become a MustInherit (abstract) class, because I need to implement a single method that must be the same for every class implementing the interface (I mean the implementation must be the same, hence I cannot use an interface anymore).
Is there a way to do this automatically, perhaps even using third party tools such as resharper (which is C# only I think?) or similar? I get a headache even thinking about the work I need to do to make this change manually[code]....
I am struggling to get inheritance to work in the way that I understand it is supposed to work.I want to create a base class that uses MustInherit. It will have properties. The derived class should have access to those properties. But how do I get and set property values for an instance of the derived class?
So I have Public MustInherit Class Baseperson
Private _Name Public Property Name as string
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But this does not provide encapsulation of the property so it would not seem to be a good solution.
I see various documentation on MSDN that talks about "abstract" classes having properties but I don't see how to make it work.
I created a vb.net dll which I am using in an unmanaged c++ project.When I try to create an object of the class, I am getting an error:cannot instantiate abstract class.Why would my class be abstract? How can I modify it so that it won't be abstract?
View 1 Replies1)When we use Overload constructors in a class
2)and which one is get execut first.
Public Class remoteobj
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i've got a Class like this public Class Cart(Of Item) Public Sub New(ByVal a As Integer, ByVal ParamArray items As Item())but i do not see how to create an instance of it: Dim block_names As New Cart(Of String, 5I)i get something like "type expected" o.O
View 2 RepliesI have one interface that contains four functions. I have about 20 classes that implement this interface. Throughout each class, I see a lot of duplicate code, for example, there are constants declared at the beginning that are in every class. The method implementations (logic) of the interface are mostly the same.It contains duplicate structures. Is this a case where I can eliminate a lot of duplicate classes by implementing an abstract class instead of an interface. What I am striving for is too be able to put common methods from the abstract class as non-abstract methods and then methods that need their own implementation would be marked over-ridable. Can I put consts and structures in abstract classes? If so, that would eliminate a lot of duplicate code across the classes. Is there anything else I should look out for in the classes as a sign that I probably should be use an abstract class instead of an interface.
View 2 RepliesI'd like to make sure each of the subclasses has a certain nested class whose actual fields are up to the developer.
Nesting an abstract class inside the base abs. class doesn't seem to do the trick because during actual coding, both the nested abs. class and the nested class in the subclass both are available (show up in intellisense).
Having the base class implement an interface that includes a class doesn't work since interfaces only refer to methods that can be implemented, not classes (meaning implementing the interface requires implements methods, but says nothing about classes in the interface.
understanding difference between an interface and an abstract class which has no function with implementation?which is better abstract cls or interface in term of speed, features..?
View 11 RepliesI am developing a web app but is not satisfied with is architecture that I am following. The architecture is plain old conventional 3 tier architecture. What i want is follow some design pattern or architecture that will be help me in decoupling my code.I have idea about MVC and MVP architectures for Web App but i need different from that. I want to use OOPS concepts using abstract classes and interfaces, polymorphism etc in my app but not MVC and MVP. I dont know why?
View 2 RepliesI've been playing around with implementing an abstract base class that using reflection accomplishes SQL to Object mapping.
I did some benchmarks and decided I wanted to implement a caching strategy for the property info of the objects (to prevent future lookups on them). My first instinct was to try and implement something like this.
Public MustInherit Class BaseModel
Implements IFillable
Private Shared PropertyCache As List(Of PropertyInfo)
[Code]....
I am trying to compile the following code and i am getting the error[code]...
View 2 RepliesBasically, I have a custom child form class which has events that will be passed to the parent. In the custom child form, I have a declaration of a "MustInherit" class that inherits the DevExpress User Control Class.
The reason for this, is I have many user controls that derive from this base class, and the child form can have an instance of any one of these controls, and doesnt care which. The only requirement is that the child form can handle the same events from each type of control the same way.
Some watered down code snippets(still pretty long unfortunately):
'''Inherited Class
Public Class ChildControlInheritedClass
[Code].....
If i have a class called A and a class called B, if B inherits A that means A is the super class and B is the subclass. I have been asked to describe why class A is not an abstract class but as i see it class A is an abstract class A, as it has been created for Class B to use in the future, is it something to do with Class B not being able to access the fields in Class A as although they are private by default?
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By Default code behind looks like --
Partial Public
Class InhAbs
[code].....
I have an abstract class in vb.net with two subclasses. In the abstract class I have a constuctor that looks like this:[code]I would like to create a second constructor that doesn't take any arguments and just initializes the args to default values.[code]When I attempt to create a new subclass using the second constructor the compiler complains that I'm missing two args to the constructor.Is there a reason I can't overload the constructor in the abstract class?
View 2 RepliesMost of our code base is in VB.NET. I'm developing a project in C# that uses a lot of the assemblies from the VB.NET code.There are three relevant classes in VB.NET:
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I am creating an xlsx reader / writer for my application (based on OpenXML SDK 2.0). I want to read xlsx files and store the data contained in each row in a DTO/PONO. Further I want to read the xlsx file and then modify it and save it.Now my problem is not with the OpenXML SDK, I can do what I need to do.My problem is on how to structure my components. Specifically I have problems with the polymorphism at the lowest level of a Spreadsheet, the cell.A cell in Excel/OpenXML can have different types of data associated with it. Like a Time, Date, Number, Text or Formula. These different type need to be handled differently when read/written from/to a spreadsheet.I decided to have a common interface for all subtypes like TextCell, NumberCell, DateCell etc.Now when I read the cell from the spreadsheet the Method/Factory can decide which type of cell to create.
Now because the cell is an abstract from the real implementation it does not know / does not need to know of what type it is. For writing / modifying the cell I solve this problem by calling .write(ICellWriter) on the cell I want to persist. As the cell itself knows what type of data it contains, it knows which method of ICellWriter it needs to call (static polymorpism).Writing to the xlsx file is no problem. My problem is, how do I get the data out of my cell into my DTO/PONO without resorting to type checking -> If TypeOf variable is ClassX then doesomething End If. As Methods / Properties have to have different Signatures and differentiating by only using a different return type is not allowed.The holder (collection, in this case a row of a table/spreadsheet) of the objects (refering to the cells) does not know the concrete implementations. So for writing a cell I pass it a Cellwriter. This Cellwriter has overloaded methods like Write(num as Integer), Write(text as String), Write(datum as Date). The cell object that gets this passed to it then calls the Write() method with the data type it holds. This works, as no return value is passed back.After some thinking about the problem I came to realize that it's not possible without reflection or knowledge of what type of cell I am expecting. Basically I was trying to recreate a spreadsheet or something with similar functionality and way too abstract/configurable for my needs.
I have recently come across some code that has the following. First there is a Interface with the following function Function Validate() As Boolean. That interface is then implemented in the an 'ABSTRACT' class like this.
Public MustOverride Overloads Function Validate() As Boolean Implements IBusinessEntity.Validate
Question 1: Why use Overloads in the Abstract class implementation.
Question 2: The Abstract class is then inherited into a class (TestClass). In TestClass the Validate function is implemented as follows Public Overloads Overrides Function Validate() As Boolean. I understand the Overrides keyword is to insure that this is the version of the Validate that you want called and not the Abstract class version but why again use the keyword Overloads?
From what I understand you can overload a constructor of a class by simply changing the constructor signature. Also, you overload Methods and Properties of a class by using the Keyword Overloads. But why do it when your implementing an Interface method, or an Abstract Class method that's inherited.
I'm trying to create a class for storing data on People with another class to store their Bank Transactions.Ideally, this all be hidden away and leave only simple statments, declarations and functions available to the programmer.[code]I know this is possible as these exist in the Listbox Class though can't figure out how it's done.
View 2 RepliesI can't make difference between public class and private class and friend and protected friend class.
View 1 RepliesI 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.
In c# you can have
public class Foo
{
public Foo(string name)
{
//do something
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Is there a VB.Net equivalent?
I have this class Public Class DGVMod Inherits DataGridView
Protected Overrides Sub OnEditingControlShowing(ByVal e As System.Windows.Forms.DataGridViewEditingControlShowingEventArgs)
MyBase.OnEditingControlShowing(e)
Try
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how variables declared with protected access in a base class are used to implement inheritance.
View 1 RepliesI am having a Friend Class InterceptingChannelBase class.It has a property as below:
Protected ReadOnly Property InnerChannel() As TChannel
Get
Return Me.innerChannelT
[code]....
This class is being inherited by (Friend Class InterceptingInputChannel) class which in turn contains another (Private Class TryReceiveAsyncResult) class.The property above is being used in this private class as below:
Public Sub New(ByVal channel As InterceptingInputChannel(Of TInputChannel), ByVal timeout As TimeSpan, ByVal callback As AsyncCallback, ByVal state As Object)
MyBase.New(channel, callback, state)
[code]....
I am getting the error on the above underlined statement saying that Protected Readonly Property InnerChannel is not accessible in this context because it is declared asa Protected.As far as i think,if i declare a property in class as 'Protected' then if this class is inherited by 'another' class then i can use this property and it should not throw an error.
I'm looking at a VB.NET class (that I didn't write) that is declared "MustInherit" (abstract in C#, I believe) that has three methods, all of which are defined as "shared" (static in C#). There are no properties or fields in the class - only the three methods. From an OO perspective, does this make any sense?
My thinking is no, because by making it MustInherit, you're essentially saying you can't create an instance of this class - you must inherit from it and create an instance of the derived class. But since all the methods are shared, you'll never actually create an instance of the parent class anyway, so the "MustInherit" does no good. You might as well not mark it MustInherit and just inherit from it whenever you want.