Property inspector. What's happening ?

[Willy Van den Driessche]

When I put an ErrorProvider (say errorProvider1) on a windows form I get new
properties on all other controls (Error on ErrorProvider1). Putting another
ErrorProvider (say ErrorProvider2) on it, adds yet more properties to them.
I'm convinced that this is intended behavior. But I'm not sure How it
happens. [for some reason I can only access my helpfiles on CD and I left
it at the office] A quick look told be it had something to do with
ProvidePropertyAttribute and the IExtenderProvider interface.

Does anybody know how it works ?
Does anybody know if there are more goodies like this ?
Does anybody have a good reference book where these things are explained ?
(not listed but explained ?) Will MS publish a series of books like the MFC
documentation (although I prefer having the rationale behind above a
reference work)


--
Van den Driessche Willy
For a work in progress :
http://users.skynet.be/wvdd2/index.html

[Kathleen Dollard]

Willy,

Actually this _is_ a really cool feature called extenders that is mostly
ignored. I did an article in VSM on this in September or October (Desktop
Developer column). I used an example of adding events, but these pups can be
widely used. They also provide ToolTips if you need an example to try to
explain to someone how they work. .

An extender is a separate component. All it has to do is fulfill hte
component interface so that it can be sited, and IExtender to provide the
pseudo-properties. A single extneder can provide multiple properties. You
can control which controls get the extender property. As interestingly, you
control what happens when the property is set. It is set when the control is
loaded, so you can do fun things like hook up events based on the property
(the point of the article), as well as the simplest case where you provide a
property that your event code can use to determine behavior.

There are some gotchas, and it took a bit of effort to figure out just how
to set up the attributes, and some of the property Set stuff is different
than I expected (annoying set/get procs rather than proper properties) so I
would suggest trying to modify an existing extender example. If you don't
have access to VSM or its archives, let me know and I will try to explain
further.

In my opinion, your gut feel that thsi was the tip of something interesting
is spot on. I think it is one of the two most innovative features in .NET
(regions being the other). They are in my bag of tricks and worth figuring
out how to use.

Kathleen

[Phil Weber]

> Actually this _is_ a really cool feature called extenders that
> is mostly ignored. I did an article in VSM on this in September
> or October (Desktop Developer column).

Kathleen/Willy: October. The article is available online here:
<http://www.devx.com/premier/mgznarch...0oct01/dt0110/
dt0110.asp>.
---
Phil Weber

[Willy Van den Driessche]

"Phil Weber" <pweber @ fawcette.com> wrote:
> > Actually this _is_ a really cool feature called extenders that
> > is mostly ignored. I did an article in VSM on this in September
> > or October (Desktop Developer column).
>
>Kathleen/Willy: October. The article is available online here:
><http://www.devx.com/premier/mgznarch...0oct01/dt0110/
>dt0110.asp>.
>---
>Phil Weber
>
>

Thanks both.
Extenders are a very handy thing for me. Up until now, I created Usercontrols
for each business object. We used the BrokenRules mechanism of Lhotka.
For each brokne rule we added a property path that identified the "most likely
wrong" property. The form was then able to use this property path to bring
focus to the visual control that "represented" the property. For this, there
was a chain of responsibility inside the usercontrols to bring focus to the
corresponding property.
I don't know inhowfar you are still following, but extenders allow me to
"set the business object property ID on the visual control". No more ugly
case statements for this one. I like it (a lot). It will be a chain of
extenders doing my work.

Come to think of it, extenders are "only possible" due to the inheritance
structure for the visual and other controls. On my toplist is also the fact
that a "TextBox" or "Control" property on a control now opens up a dropdown
in the form designer. That eliminates some coding too. My problem will
be how to control this box of Pandora. Those are possibilities we didn't
have in VB6 (you could code property pages of course) and now we have a lot
more things to decide when designing an application.

As I said in a previous post, the errorprovider can help me even further
with showing validation errors. (we do it now by showing/hiding image controls
which is nice for the user but not for the programmer) Cool.

See you both and thanks again,
Van den Driessche Willy