Veeam® is happy to provide the Microsoft community with a study guide prepared by MVP and MCT, Orin Thomas. This guide will take you through each of the exam objectives, helping you to prepare for and pass the examination.
Solved
Nested Event Handling
Posted on 2007-12-03
I have a class that contains a collections of objects (another class).
In the base collection I have several event handlers that I want to be able to pass through the collection class to the form that will call the creation of the collection.
I have the events created in the base class, I am not sure how to pass the events through the collection class.
In the attached snippet I have quickly written a small sample of what I am trying to do.
My thought is that I will have to add Event Handlers to the collection class to capture the base classes events. I would have to create corresponding events in my collection class and then I would raise the events in the handlers I created in the collection class. This would allow the form that I want to have finally handle the events.
Is there any way I can just see the base classes events from the form? this seems like it is a little much to do to pass events through.
any help would be appreciated.
In the base collection I have several event handlers that I want to be able to pass through the collection class to the form that will call the creation of the collection.
I have the events created in the base class, I am not sure how to pass the events through the collection class.
In the attached snippet I have quickly written a small sample of what I am trying to do.
My thought is that I will have to add Event Handlers to the collection class to capture the base classes events. I would have to create corresponding events in my collection class and then I would raise the events in the handlers I created in the collection class. This would allow the form that I want to have finally handle the events.
Is there any way I can just see the base classes events from the form? this seems like it is a little much to do to pass events through.
any help would be appreciated.
Example:
Public objClass as Class
'Events
Public Event StartMakingClass ()
Public Event FinishedMakingClass ()
Public Sub New()
RaiseEvent StartMakingClass ()
'Do some stuff, may take a while
RaiseEvent FinishedMakingClass ()
End Sub
End Class
Public Class objClassCollection
Private mobjClasses as New System.Collection.ArrayList
Default Public Property objClassClasses (Index as Integer) as objClass
Get
Return CType(mobjClasses(Index), objClass)
End Get
Set(ByVal Value As objClass)
mobjClasses(Index) = Value
End Set
End Property
Public Sub New()
For x as int16 = 1 to 100
Dim aobjClass as New objClass
mobjClass.Add(aobjClass)
Next x
End Sub
End Class
[X]
Welcome to Experts Exchange
Add your voice to the tech community where 5M+ people just like you are talking about what matters.
- Help others & share knowledge
- Earn cash & points
- Learn & ask questions
2
4 Comments
It's been a while since you posted this, so I don't know if you already came up with a solution. I've been hesitant to contribute because I haven't learned dotnet yet. But I had some ideas on what you could do, if my memory about dotnet capabilities is correct.
If I remember correctly, dotnet supports the ability to define parameterized constructors -- that is, when instantiating an object, you can pass a parameter to it which can be utilized by the constructor (as opposed to VB6, which requires that the object be instantiated before you can pass anything into it).
If that is correct, then you could do something like this:
1. In objClassCollection, define "callback" procedures for your two events that accept an objClass argument:
(VB6 syntax)
Public Sub StartMakingClass(Obj As objClass)
End Sub
Public Sub FinishedMakingClass(Obj As objClass)
End Sub
2. In objClass, create a parameterized constructor that accepts an objClassCollection argument:
(I have no idea what the syntax would be, but essentially what you want to do is store the reference to the objClassCollection object, inside of each objClass instance.)
3. In objClass, instead of raising an event, directly call the StartMakingClass or FinishedMakingClass procedures of the objClassCollection object, which you've got a reference to inside each objClass object.
(VB6 syntax -- assuming the local variable holding the objClassCollection object is called mParent)
mParent.StartMakingClass Me
(or)
mParent.FinishedMakingClas
4. In the objClassCollection object define the two events, then raise them from within the StartMakingClass and FinishedMakingClass procedures:
(VB6 syntax)
Public Event StartMakingClass ()
Public Event FinishedMakingClass ()
Public Sub StartMakingClass(Obj As objClass)
RaiseEvent StartMakingClass
End Sub
Public Sub FinishedMakingClass(Obj As objClass)
RaiseEvent FinishedMakingClass
End Sub
Now your form would declare the objClassCollection object WithEvents so that it can respond to these "events" from the individual objClass objects, channeled through the objClassCollection object.
Not sure if you can use any of this, but hope it helps.
If I remember correctly, dotnet supports the ability to define parameterized constructors -- that is, when instantiating an object, you can pass a parameter to it which can be utilized by the constructor (as opposed to VB6, which requires that the object be instantiated before you can pass anything into it).
If that is correct, then you could do something like this:
1. In objClassCollection, define "callback" procedures for your two events that accept an objClass argument:
(VB6 syntax)
Public Sub StartMakingClass(Obj As objClass)
End Sub
Public Sub FinishedMakingClass(Obj As objClass)
End Sub
2. In objClass, create a parameterized constructor that accepts an objClassCollection argument:
(I have no idea what the syntax would be, but essentially what you want to do is store the reference to the objClassCollection object, inside of each objClass instance.)
3. In objClass, instead of raising an event, directly call the StartMakingClass or FinishedMakingClass procedures of the objClassCollection object, which you've got a reference to inside each objClass object.
(VB6 syntax -- assuming the local variable holding the objClassCollection object is called mParent)
mParent.StartMakingClass Me
(or)
mParent.FinishedMakingClas
4. In the objClassCollection object define the two events, then raise them from within the StartMakingClass and FinishedMakingClass procedures:
(VB6 syntax)
Public Event StartMakingClass ()
Public Event FinishedMakingClass ()
Public Sub StartMakingClass(Obj As objClass)
RaiseEvent StartMakingClass
End Sub
Public Sub FinishedMakingClass(Obj As objClass)
RaiseEvent FinishedMakingClass
End Sub
Now your form would declare the objClassCollection object WithEvents so that it can respond to these "events" from the individual objClass objects, channeled through the objClassCollection object.
Not sure if you can use any of this, but hope it helps.
Or you could pass a reference to the form, into each objClass, and then put the callback procedures on the form instead of the collection.
Featured Post
Question has a verified solution.
If you are experiencing a similar issue, please ask a related question
Enums (shorthand for ‘enumerations’) are not often used by programmers but they can be quite valuable when they are.
What are they?
An Enum is just a type of variable like a string or an Integer, but in this case one that you create that contains…
This article describes some techniques which will make your VBA or Visual Basic Classic code easier to understand and maintain, whether by you, your replacement, or another Experts-Exchange expert.
Get people started with the process of using Access VBA to control Outlook using automation, Microsoft Access can control other applications. An example is the ability to programmatically talk to Microsoft Outlook. Using automation, an Access applic…
Show developers how to use a criteria form to limit the data that appears on an Access report. It is a common requirement that users can specify the criteria for a report at runtime. The easiest way to accomplish this is using a criteria form that a…
Suggested Courses
Course of the Month15 days, 3 hours left to enroll
649 members asked questions and received personalized solutions in the past 7 days.
Join the community of 500,000 technology professionals and ask your questions.