Yet another C# WTF moment: UserControls

bonkey

So, I'm developing some userControls as part of something I'm building. They're kinda neat really. Here's the thing though....

A lot of these controls have common functionality. SO I thought I'd be smart, and define a BaseParameterControl, and then derive my various XParameterControl classes from it. So far so good. OK - I have to have a no-parameter constructor, which I don't really want, but I can live with that.

Then I discovered a really cool shortcut I could take if I had some abstract members implemented in the base control....so I set it to abstract, add the abstract method signatures...compile...all looks fine.

Then I try opening a *derived* class in teh designer. That doesn't work. Nope. It tells me that it failed because it couldn't create an instance of hte base control, cause its abstract. Seems a bit stupid, but hey...

However...

if I try opening the *abstract* class in the designer, guess what....it opens just fine.

OK. Screw it. I can live with this...I'll just de-abstract my base class, and implement an interface across all of the derived ones. That solves that...as long as I forget to think *why* this might be happening.

Next trick....I decide to add an event. So, I declare it in the base class. But guess what...this means I can't raise it in the derived class!!! Again, some WTFness ensues, and eventually I give up, wrap the call to the event in a method which does nothing except raise the event....and *this* I can call from the derived class without problems...

If anyone knows *why* this behaviour is correct/necessary...I'd be interested....

jc

dazberry

bonkey wrote:

Then I discovered a really cool shortcut I could take if I had some abstract members implemented in the base control....so I set it to abstract, add the abstract method signatures...compile...all looks fine.

Then I try opening a *derived* class in teh designer. That doesn't work. Nope. It tells me that it failed because it couldn't create an instance of hte base control, cause its abstract. Seems a bit stupid, but hey...

However...

if I try opening the *abstract* class in the designer, guess what....it opens just fine.

Although this is essentially a joke - look at warning #7
http://www.bbspot.com/News/2004/11/top_11_c_sharp_compiler_warnings.html

bonkey

Lol.

As an aside...I've also noticed that my compiler gives me warnings on three forms where there's a variable thats never initialised.

The variable? The System.ComponentModel.Container components one, which the designer insists is absolutely, positively needed.

Fscking thing.