Event Handling An Abstract Class?
Jul 6, 2010
Basically, 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].....
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Dec 1, 2011
I have an event defined and firing in class B
Public myEvent()
In class A:
Private WithEvents _b as B
Private Sub hander() Handles _b.myEvent
but, this handler does not get called.
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Jul 24, 2010
I have a custom class which basically manages the program settings.
In it's New() event, I'm performing a check to see whether a value stored in My.Settings is the same as the default value (I made sure the value wasn't!), if not then it will perform a RaiseEvent ValueChanged().
On my form, I have an instance of the class declared "Private Withevents ProgramSettings as New clsProgramSettings", I also have a handler "Private Sub DoSomething() Handles ProgramSettings.ValueChanged" declared.
When I run the program the form gets loaded, the instance is created, the RaiseEvent is called, but the handler is not receiving the event?
I tried "Private Withevents ProgramSettings as clsProgramSettings", then creating the instance in the Form.Load(), but still no success!?
Is there something I'm doing wrong, or is there a problem with the IDE? I'm using VS 2010.
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Jan 6, 2010
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?
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Jun 2, 2009
I am trying to implement a service object class for the POS for .NET library using VB9. Specifically, the BillDispenser class. I define my class and inherit from Microsoft.PointOfService.BillDispenser. As normal, it creates stubs for all the MustOverride (abstract) properties and methods that I need to override (I love that), EXCEPT for the events. Apparently thare two events defined as abstract (MustOverride) in the POSCommon base class, but VB doesn't generate stubs for them.[code]...
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Jun 2, 2009
Ok, I've been searching all over the web for an answer to this and I'm getting nowhere. I've found several examples and tried code translators, but they either fail to compile at all (syntax is wrong) or fail to solve the problem. Here is what I am up against:
I am trying to implement a service object class for the POS for .NET library using VB9. Specifically, the BillDispenser class. I define my class and inherit from Microsoft.PointOfService.BillDispenser. As normal, it creates stubs for all the MustOverride (abstract) properties and methods that I need to override (I love that), EXCEPT for the DirectIOEvent. Apparently this event is defined as abstract in the POSCommon base class, but VB doesn't generate a stub for it.
No compile errors are generated from not defining it, but I get the following runtime error as soon as my unit test attempts to load the dll[code]...
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Mar 30, 2011
I 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.
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Sep 8, 2011
I'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.
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Jan 31, 2011
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..?
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May 13, 2010
I 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?
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Mar 4, 2011
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.
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Jan 19, 2012
I'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]....
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Mar 31, 2010
I am trying to compile the following code and i am getting the error[code]...
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Dec 28, 2011
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?
[Code]...
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Aug 25, 2009
By Default code behind looks like --
Partial Public
Class InhAbs
[code].....
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Nov 19, 2010
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?
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Jul 5, 2009
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.
[Code]...
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Feb 28, 2011
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.
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Oct 7, 2011
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.
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Feb 15, 2011
I have alot of experience in working in VBA for excel, but not so much experience in creating my own structures so it's all still a bit foggy. I'm trying to capture the event for when the F1 key is pressed, not just when the form is active, but anytime the program is running. The code below expressing the handling is automatically generated for me in VB Express... But I'd like to change the situation to encompass anytime the program is open. I guess I have to reference events that happen in windows in general, but i don't know how to do it. I think i have to create the even in a class module?
[Code]...
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Jan 16, 2009
i declared a global variable button:
Dim button1 As New Button()
Now, i dont know how to add a click event in this button since it is a variable.
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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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Sep 21, 2011
I'm completely confused about the event handling. I read some articles about it but after it I just get confused to write and use them in my classes.This is my class i. e.:
[Code]..
I dont have any argument passing. But I want to know how should I do it too. And I wanted to know if each instance of the Test class, run this event separately I mean each instance by themselves, This event AnEvent() will occur? Cuz I have lots of instances from my class.
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Aug 31, 2010
I am developing a COM dll library, and I have a little vb.net (vs 2005) application just to test it.I had my object declared in the application as
Private m_VarName As MyLib.CMyComClass
So far, so good.But now, I need an event to inform the application of some things, so I implemented such event in the COM dll, and changed the declaration to
Private WithEvents m_VarName As MyLib.CMyComClass
So far, so good, again. But if I add a Sub to handle my event:
Private Sub m_VarName_OnCaptureStop() Handles m_VarName.MyEvent
..
End Sub
The first time I create the object, nothing bad happens, but if I reinstantiate it
If (Not m_VarName Is Nothing) Then ReleaseComObject(m_VarName)
m_VarName= New MyLib.CMyComClass
then I get a cryptic TargetInvocationException, seemingly related to reflection (which, AFAIK, I am not using).If I remove the "Handles m_VarName.MyEvent" part, everything seems to work. In case it matters, I am not firing any event, for now.
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Nov 18, 2010
NET gurus... How would you convert this very chunk into VB?
[Code]...
When I use an online converter (Telerik), the middle line converts like this: Me.timer.Elapsed += New System.Timers.ElapsedEventHandler(ManageThreads) with 2 errors:
1- "Public eventElapsed is an event and cannot be called directly. Use raiseEvent
2- Delegate requires an Adess Of expression. Do I simply add "Address Of" ?
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Dec 15, 2011
I've been trying to figure out how to get this control to work for over a week. It can be found here: A Professional Calendar/Agenda View That You Will Use - CodeProject. It's a calendar/scheduler control that was designed using c# and I'm trying to use it in my vb.net app. I've sucessfully created a dll and have referenced that dll in my project and am able to see the controls in the toolbox as well as put them on my form. My problem is that I can't get ANY of the code that I wrote in the form to fire. No event handlers will work, not even the form_load which handles the mybase.load event. Nada. f a reason that this might be? How do I sucessfully add a handler to the events? I've used <code> addhandler monthView1.SelectionChanged, addressof (and nothing I put here ever works) </code>
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Jun 15, 2009
I have come accross many scenarios of handling datagridviewcombobox events, however none seem to fit my scenario, or I may be missing something.1. I need to capture the column index that the combobox is resident in. This is because I have a complete row of comboboxes that should set the header text to the selected value.here is the code I have so far:' I also use a list of string as datasource publicly declared
Public cs As New List(Of String)
'to insert the combo's into the grid
Dim row As New DataGridViewRow
cs.add("Book")
cd.Add("Author")
[code]....
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May 27, 2011
how to write below in vb.net??
Me.connection = New RAPI
connection.ActiveSync.Active += new ActiveHandler(ActiveSyncActive);
Private Sub ActiveSyncActive()
..................
End Sub
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May 7, 2009
I can come up with, if I understood the solution better, I could probably phrase a better subject line.[code]...
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Jan 8, 2009
I haven't done any programming in a while, and I have pretty much 0 experience with databases, so I'm hoping I can get some guidance with what I'm trying to achieve.I have a class (or want to have) which represents a person, for each person there's multiple dates, and for each date there's multiple events which have properties like time, place, duty, etc. I want to be able to save and load this from a database using a form. I want it to be able to function where I can type in the person's name and it will load all the data into the form, which has a combo box for the different dates and events, and when I select a different date and/or event I want the data to change correspondingly.
If someone could just give me a push in the right direction as to where I should be looking for help in achieving that I would really appreciate it. I don't have the class made to do any of that, just an idea of how it will function. I haven't worked much with classes, so I'm not sure how to approach it. Meaning I need guidance with classes and databases alike.
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