Inheritance and Interfaces

[gwolinsky]

I originally posted this in the WindowsForms group but that may not
have been the best place to post it. So, I am reposting here.

--------------------------------------

I am trying to implement the new INotifyProperty Changed interface in my
custom business object. The problem I'm having is with the inheritance
model.

I have a base object called "Person". The object "Employee" inherits
from person and provides additional properties and methods.

I implemented INotifyProperty Changed in the Person base class and
everything worked great. However, how do I implement it in the derived
"Employee" class.

If I implement it the same way, the compiler warns that:

"event 'PropertyChange d' conflicts with event 'PropertyChange d' in the
base class 'Person' and should be declared 'Shadows'."

OK. So I change the event definition to "Shadows". Then, I still get
the following warning:

"'System.Compon entModel.INotif yPropertyChange d.PropertyChang ed' is
already implemented by the base class 'Common.Person' .
Re-implementation of event assumed."

If I ignore BOTH warnings and run it, it works fine. If I designate
the event as "Shadows" and run it, it works fine.

Am I doing this correctly or am I in high weeds?

Any help would be greatly appreciated.

Sincerely,
Glen Wolinsky

[Jay B. Harlow [MVP - Outlook]]

Glen,
| So, in order to be consistent, are you saying I should initialize the
| "properties " (not the backing variables) in a subroutine that is called
| by both the constructor AND the "Get" routine?
Yes.
--
Hope this helps
Jay [MVP - Outlook]
..NET Application Architect, Enthusiast, & Evangelist
T.S. Bradley - http://www.tsbradley.net
"Glen Wolinsky" <gw*******@mill ermartin.com> wrote in message
news:uV******** ********@TK2MSF TNGP10.phx.gbl. ..
| Jay,
|
| There are two ways my objects are initialized:
|
| 1. If this is a "get" operation, the object loads the employee data from
| the database and sets all the backing fields;
|
| 2. This is a new employee and the backing fields are initialized during
| variable instantiation.
|
| Option 2 should be full of errors since it's empty and there are several
| required fields. Option 1 would have to use the properties instead of
| the backing fields like you mentioned in order make sure the current
| data is valid.
|
| So, in order to be consistent, are you saying I should initialize the
| "properties " (not the backing variables) in a subroutine that is called
| by both the constructor AND the "Get" routine?
|
| Thanks,
| Glen
|
| --
| Sent via .NET Newsgroups
| http://www.dotnetnewsgroups.com

[Glen Wolinsky]

Jay,

You have been a tremendous help. Thank you and God bless.

Sincerely,
Glen Wolinsky

--
Sent via .NET Newsgroups
http://www.dotnetnewsgroups.com

[Glen Wolinsky]

Jay,

Just when you thought it was safe to back into the forum.....I'm back.
;o)

I am implementing the solution we discussed. Everything seemed to be
working fine except for one issue.

My boss did not like the fact that on a NEW employee, the data entry
screen came up not only blank (as it should be) but with ALL the error
indicators already on (because I run the Employee.Valida te routine
during construction that validates everything in the object). What he
wanted was that when the entry screen initially appears, there are no
validation errors. Then as the user attempts data entry, the validation
happens on a per-field basis. If the programmer attempts to run the ADD
or UPDATE routines in the Employee object, the object runs that full
validation routine and if it's NOT valid throws an exception.

I thought, "Ok, I'll just NOT run the full validation when the employee
object is constructed. Then, the individual property set routines will
validate on each one." Well, the problem is that when the user is
tabbing through blank fields (which shouldn't be blank) the values
aren't changing so the validation routines aren't running and the
errorproviders aren't showing.

Now for even stranger things. I put a test button on the form. This
button does nothing but run the employee object's full validate routine
(mentioned above) which just runs the validation routines on ALL the
properties. I thought this would make all the validators show up, but
they don't!!

Now, after trying that full validation, I change any field on the form
so that the validation fires, ALL the OTHER validations suddenly
appear!!!

I also found that when I use that test button to try and validate
EVERYTHING, if -- in the employee object -- I run the OnChangedProper ty
event for each property after the property is validated, the
errorproviders show up.

Does any of this make sense? If so, do you have any more tricks in your
bag?

As before, your help would be grealy appreciated.

Sincerely,
Glen
--
Sent via .NET Newsgroups
http://www.dotnetnewsgroups.com

[Phill. W]

<gw*******@mill ermartin.com> wrote in message
news:11******** *************@g 49g2000cwa.goog legroups.com...

I implemented INotifyProperty Changed in the Person base class and
everything worked great. However, how do I implement it in the
derived "Employee" class.

This may be too little, too late, but I'll pitch in anyway in the hope
that, if I've been doing it completely wrong[ly?], someone will set
me straight.

I implement the Interface in the Base class, but make the
"implementi ng" routine Overridable. Each subclass can then supply
its own implementation that gets used instead of that in the Base class.

Class base
Implements ISomeInterface
Private Overridable Sub s1() _
Implements ISomeInterface. s1
. . .
End Class

Class derived
Inherits base
Private Overrides Sub s1()
. . .
End Class

Comments/Suggestions/derisory laughter, anyone?

Regards,
Phill W.

[Glen Wolinsky]

Phill,

In my numerous mutations of the code I was working with, I tried exactly
what you described. At least in regards to the IDataErrorInfo
interface, the behind-the-scenes wiring didn't work properly in the
subclasses or class-properties. Of course, it's entirely possible that
there was something else wrong with the code I tried.

My .02

Sincerely,
Glen
--
Sent via .NET Newsgroups
http://www.dotnetnewsgroups.com

[Jay B. Harlow [MVP - Outlook]]

Jay,
| Does any of this make sense? If so, do you have any more tricks in your
| bag?
Yes it makes sense, unfortunately I have not yet had time to look at it to
offer any sound advice.

--
Hope this helps
Jay [MVP - Outlook]
..NET Application Architect, Enthusiast, & Evangelist
T.S. Bradley - http://www.tsbradley.net
"Glen Wolinsky" <gw*******@mill ermartin.com> wrote in message
news:%2******** ********@TK2MSF TNGP10.phx.gbl. ..
| Jay,
|
| Just when you thought it was safe to back into the forum.....I'm back.
| ;o)
|
| I am implementing the solution we discussed. Everything seemed to be
| working fine except for one issue.
|
| My boss did not like the fact that on a NEW employee, the data entry
| screen came up not only blank (as it should be) but with ALL the error
| indicators already on (because I run the Employee.Valida te routine
| during construction that validates everything in the object). What he
| wanted was that when the entry screen initially appears, there are no
| validation errors. Then as the user attempts data entry, the validation
| happens on a per-field basis. If the programmer attempts to run the ADD
| or UPDATE routines in the Employee object, the object runs that full
| validation routine and if it's NOT valid throws an exception.
|
| I thought, "Ok, I'll just NOT run the full validation when the employee
| object is constructed. Then, the individual property set routines will
| validate on each one." Well, the problem is that when the user is
| tabbing through blank fields (which shouldn't be blank) the values
| aren't changing so the validation routines aren't running and the
| errorproviders aren't showing.
|
| Now for even stranger things. I put a test button on the form. This
| button does nothing but run the employee object's full validate routine
| (mentioned above) which just runs the validation routines on ALL the
| properties. I thought this would make all the validators show up, but
| they don't!!
|
| Now, after trying that full validation, I change any field on the form
| so that the validation fires, ALL the OTHER validations suddenly
| appear!!!
|
| I also found that when I use that test button to try and validate
| EVERYTHING, if -- in the employee object -- I run the OnChangedProper ty
| event for each property after the property is validated, the
| errorproviders show up.
|
| Does any of this make sense? If so, do you have any more tricks in your
| bag?
|
| As before, your help would be grealy appreciated.
|
| Sincerely,
| Glen
|
|
| --
| Sent via .NET Newsgroups
| http://www.dotnetnewsgroups.com