C / C++ / MFC

Re: XP Style progress dialog

10-Mar-02 11:52

I haven't tried it myself, but maybe playing with extended styles WS_EX_LAYOUTRTL or WS_EX_RTLREADING for the progress bar control one manages to have the bar drawn in right-to-left direction. From this and with a little code it's not hard to replicate the "Knight Rider car" effect you're after.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Ravi Bhavnani10-Mar-02 12:33

Ravi Bhavnani

10-Mar-02 12:33

I haven't seen the XP progress dialog, but if you're looking for a progress control that works like Netscape's "infinite" progress bar, check out:

/ravi

"There is always one more bug..."
http://www.ravib.com
ravib@ravib.com

design pattern problem

10-Mar-02 9:33

Who can offer a design pattern to solve the following problem:
1. I have a class which is a singleton
2. this class manages a collection (map) of objects.
3. each object is a subject
4. I have another class who uses the singleton from step 1 which is an observer of the objects from step 2
5. in some point of the flow, an object from step two decided it is finished. it notifies it's observer from step 4.
6. the observer from step 4 performs some action based on the recieved notification and now it needs to delete the object that notified him that it was finished doing it's work, BUT (and here's the problem): it cannot delete it since the object from step 2 is in the middle of it's notification loop. the class from step 4 doesn't know if there are other observers and need not care about it. How can I break the notification loop and delete the object which sent the notification safly ?
Now, please don;t offer me to use a message loop or a message queue and a timer since it is out of the question for my current design.
Thanks.

Shoval Lior.

Paul M Watt10-Mar-02 9:53

Paul M Watt

10-Mar-02 9:53

Do you have multiple observers that are trying to delete the object from step two, or do the other observers simply react to the notification?

If you have multiple observers, I would add reference counting to the managed object of step two, and each observer that observes this object will increment the count. Then when it gets the notification to stop observing, it will 'release' its reference count.

In your managed object of step two, when all of the references are released, then it will delete itself with delete this, or what ever other mechanism you have set up.

10-Mar-02 18:07

Currently there are no other observers, but some day they might be.
The main problem is not deleting the object, but breaking the notification loop.
How do I accomplish that ?

10-Mar-02 10:07

Hi,
could't it be done like this ?

...
5. in some point of the flow, an object from step two decided it is finished. it notifies it's observer from step 4.
6. the observer from step 4 performs some action based on the received notification and then returns a "special value" meaning that the object has to delete itself.
7. the calling object receives the "notification's return", and if it is the "special value", it deletes itself...

Lion.

10-Mar-02 18:08

What do you mean by "6. the observer.... returns a "special value"...."
I don't know of any way an observer can return something to the notifying subject. That's not how my Observer pattern is implemented..
Any other idea ?
Thanks.

Ravi Bhavnani10-Mar-02 10:43

Ravi Bhavnani

10-Mar-02 10:43

The observer could notify the singleton that it is "finished" with the object. The singleton could then decide what to do - it would probably pass on the message to the object, which would inform other interested observers of the fact. The object can then delete itself. If it does so, it should inform its (other) observers that it's no longer available for use.

/ravi

"There is always one more bug..."
http://www.ravib.com
ravib@ravib.com

10-Mar-02 18:12

All is well, but it doesn't change the fact that it still does't break the notifications loop.
Think of this as the flow of events:
1. Subject starts it's notification loop
2. it reaches my observer is the list of observers and notifies it
3. the observer then notifies the singleton needs to be deleted
4. the object is deleted
5. the function (in the singleton and in the observer) returns and the next thing to do is for the subject to continue it's notification loop on to the next observer on the list, but then the program crashes on access violation since the memory space the subject has occupied is not longer allocated since it was deleted / has deleted itself.

Please try something else.
Thanks,
Lior.

10-Mar-02 18:13

check out my reply to the previous message I received.
In short, it still doesn't break the notifications loop.
Thanks,
Lior.

Joaquín M López Muñoz10-Mar-02 10:58

10-Mar-02 10:58

IMHO there's a conceptual mismatch here that's causing your problems: You have an observer entitled to delete the subject (so it is a rather powerful observer) but that might be sharing the observation with other observers. The design seems to fail to capture the special role played by this observer. Maybe you can transfer the responsibilty of deleting subjects to the singleton class that holds them, and keep the observers as passive objects, which is (as I see it) what this design pattern originally intends.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

starting a thread

10-Mar-02 9:31

I'm getting the error message:
'Cx::Cx' : cannot access protected member declared in class 'Cx'

I used the classwizard to create a CWinThread derived class Cx.
And I see that i places the construtor in the protected section.

Now I read that there were two ways to start the thread, one that uses AfxBeginThread /ResumeThread and this one:

Cx * thread = new Cx();
thread->m_x = 1;
thread->CreateThread();

I like this implimentation and would like to get it to work but I'm not sure how.

Re: starting a thread

Paul M Watt10-Mar-02 9:55

Paul M Watt

10-Mar-02 9:55

Anonymous wrote:
And I see that i places the construtor in the protected section

You placed your constructor in the protected section or the class wizard did?

It seems to me that the contstructor should be in the public section.

Re: starting a thread

10-Mar-02 10:45

Thats a typo, the sentance should read:
And I see that IT places the construtor in the protected section.

it = classwizard.

>It seems to me that the contstructor should be in the public section.
Yeah, thats what i thought (which is why i included that bit of info about the location of the constructor) but thats what the classwizard does so i don't want to go and change it.

So my question in the first post still stands.

Re: starting a thread

Paul M Watt10-Mar-02 18:49

Paul M Watt

10-Mar-02 18:49

I am not a big MFC programmer, but MSDN says that AfxBeginThread will create the instance of the object for you.

Member var/func deletion

Travis D. Mathison10-Mar-02 8:14

Travis D. Mathison

10-Mar-02 8:14

I can't believe this trivial/basic task is giving me trouble! I've figured pretty much everything else out -- but .. in VC++.NET how do you properly delete a classes member functions and variables?

Travis D. Mathison ---
--- After three days without programming, life becomes meaningless ...

Joaquín M López Muñoz10-Mar-02 8:33

10-Mar-02 8:33

Appart from any other IDE-assisted methods, you can always go to the corresponding .h and .cpp files and manually erase the occurrences of the member.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo

Travis D. Mathison10-Mar-02 8:31

Travis D. Mathison

10-Mar-02 8:31

That's what I am doing now. I'm simply wondering where the IDE assisted feature for it is ..

Travis D. Mathison ---
--- After three days without programming, life becomes meaningless ...

Joaquín M López Muñoz10-Mar-02 8:41

10-Mar-02 8:41

Yes, I should have guessed. I don't know, I'm sorry I can't be more helpful.

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo