Only one instance of my control per Page

[Zarko Gajic]

Hi, what's the best practice of ensuring that only one instance of a
(custom) control can be placed on a Web form (either at design or run time)?

~ Zarko

 

[Brock Allen]

Hmm, interesting requirement.

At runtime you could put a flag in the HttpContent.Items collection to indicate
that there is one on the page already. Perhaps you'd set this in the ctor
or in Init event for the control. This would work since the Items collection
is a per-request bag of data that is recreated for every request. This is
the first idea off the top of my head, but I don't know how much I like it....

What's the exact requirement? And why exactly is this a requirement? I'm
curious...

 

[Zarko Gajic]

Brock,

My idea was to have a static field that would increment in the constructor
.... this way I could count the number of instances "from inside" my control.
I'm just not sure where to decrement the counter (destructor? does it get
called in the designer when you remove the control - haven't tried that
yet.)

I'm developing a simple IExtenderProvider for System.Web.UI.Page - there's
no point of having two on the page.

~zarko

 

[Antonio Bakula]

Brock,

My idea was to have a static field that would increment in the constructor
... this way I could count the number of instances "from inside" my control.
I'm just not sure where to decrement the counter (destructor? does it get
called in the designer when you remove the control - haven't tried that
yet.)

I'm developing a simple IExtenderProvider for System.Web.UI.Page - there's
no point of having two on the page.

maybe singleton pattern is what you wont ? I didn't work with singleton
controls, only singleton objects but maybe this is solution

http://www.yoda.arachsys.com/csharp/singleton.html

 

[Zarko Gajic]

Hi, what's the best practice of ensuring that only one instance of a

(custom) control can be placed on a Web form (either at design or run

time)?

To all concerned:

Solved, using class static integer variable to count the number of
instances. The variable increments in constructor , decrement in destructor
(Dispose overridden) ... Render used to test for the number of instances.

~Zarko

 

[Brock Allen]

Well, the static would get incremeneted for two users hitting two different
pages at the same time, and so I don't think this would work for your requirements.
Also, there is no notion of deterministic finalization (like a dtor from
C++) in .NET. You might be able to handle the Unload event on your control,
but I suppose there are situations where that would not get called, so no
guarentees.

I still think the per-request Items collection is your best bet. This won't
help at design time, though.

 

[Brock Allen]

What happens when two different users are accessing that page at the same
time? The static variable is shared across all instances of your control.
Maybe you've already accounted for this...?

 

[Zarko Gajic]

Brok,

I still think the per-request Items collection is your best bet. This won't
help at design time, though.

I've mixed the two approaches: at design time .. an instance counter is
used; at run time .. Context.Items is used (as you suggested).

p.s.
I've run a few test and this seems to work ...

~Zarko