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Is Subclassing Required In Order To Do This?

Posted on 1998-06-01
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Last Modified: 2010-05-03
I have two VB applications(call them A and B), and I want A to be notified when B gets focus(and A loses focus).  Is there a VB event within application A I can generate when this happens?  Do I have to use windows subclassing?  I would like to avoid subclassing if I can.  

Furthermore, if I have to subclass, what's the best way to do this? I know that the message I need to subclass is WM_ACTIVATEAPP or WM_ACTIVATE.  Do I need to purchase a third party OCX?  

Please Advise,

Thanks.
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Question by:debbyt
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by:clifABB
ID: 1462249
Well, you don't *really* have to subclass.

You could let B write to an ini file when it changes focus and have A constantly poll (through a timer control) the ini file for a change in B's focus.

But subclassing is so much easier on the resources.
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by:debbyt
ID: 1462250
I know I can use a timer to poll for the name of the foreground window with an API call, but this is very wasteful especially when there's no way to know when the focus will change.

So is subclassing the only reasonable way?
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kamall earned 100 total points
ID: 1462251
debbyt,
One way is to use DDE between the two applications. (I am not good in DDE), but you should find some examples in the VB samples directory.
The second way is to use a timer in application A, and check for its Title. In app. B, you can simply use the SetWindowText API  to change the title of the A application (for example, append a space to the end of the title). Now reading the title of A in its timer event, you get the notification, and reset its title.
Hope that helps.
Regards
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by:kamall
ID: 1462252
The
"In app. B, you can simply use the SetWindowText API  to change the title of the A application"
means
"When app B gets the focus (your form in app. B), you can simply...."
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by:clifABB
ID: 1462253
Yep.  That's why I said it was easier on the resources.

I did some tests and, apparently, you'll have to have a third-party control such as MessageBlaster (a shareware ocx available at various shareware sites) or Spyworks (available from Desaware - www.desaware.com)

Once you retrieve one of these, let us know if you need some help subclassing.
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