[DUG] Shellexecute question

[Jolyon Smith]

This doesn't really establish anything other than what we already know...
that it is incredibly difficult to reliably anticipate in one thread
something that is happening in some other thread.

Prog A > launch Prog B

In simplistic terms you now have two threads, let's call them Thread A and
B (corresponding to each program, A and B).  If Thread A now does something
that might interfere with/be interefered with by something occuring on
Thread B then if you want any sort of reliable behaviour there has to be
some co-ordination between the threads.  Anything else is built on an
assumption or set of assumptions that may or may not be valid at any given
time.

In this case, if Thread A tries to SetForegroundWindow() because it
believes that Thread B has "stolen" it, then it's attempt to steal it back
is only going to succeed if the call to SetForegroundWindow() occurs AFTER
Thread B has in fact stolen it.  If Thread A reclaims the focus BEFORE
Thread B has nicked it, then Trehad B is still going to end up stealing the
focus.

Thread A can build in an assumption that if it waits a certain amount of
time then Thread B will probably have completed it's stealing activity, but
this is still an assumption and is just as vulnerable to failure.




On 25 July 2014 16:17, russell <russell at belding.co.nz> wrote:

> *I also tried Russells suggestion about setting the foreground window and
> it don’t work for me (Windows 8.1)*
>
>
>
> I tested this earlier on W7 by starting another program, so my main
> program lost focus. My main program was triggering
> SetForegroundWindow(forms.application.mainWindow.handle)
> from a timer and it worked OK. That is, focus returned to my main program
> when the timer went off.
>
> Just now I ran
> bcdShellExecute(<path toExcel>);
> SetForegroundWindow(forms.application.mainWindow.handle);
> and focus was not returned to my main program, it stayed with Excel.
>
> As a guess I tried
> bcdShellExecute(<path toExcel>);
> Sleep(150);
> SetForegroundWindow(forms.application.mainWindow.handle);
> and focus was returned to my main program. We can each guess what this
> means about interrupting a starting program in W7.
>
> I tried a similar test on W8.1 and focus is not returned to my main
> program even using sleep(1250).
>
> R
>
> *From:* delphi-bounces at listserver.123.net.nz [mailto:
> delphi-bounces at listserver.123.net.nz] *On Behalf Of *John Bird
> *Sent:* Friday, 25 July 2014 12:22 a.m.
>
> *To:* NZ Borland Developers Group - Delphi List
> *Subject:* Re: [DUG] Shellexecute question
>
>
>
> Hey that should have been perfect, as I already was doing SW_SHOWMINIMIZED
> which works fine, and so does SW_SHOWNOACTIVE  which also does what it
> should – start the other window but not change focus.
>
>
>
> However SW_SHOWMINNOACTIVE doesn’t work.   Now the other program is a
> Delphi program of mine that does some initialisation in the Formshow event
> (turning on timers etc) and I am wondering if somehow the event doesn’t
> fire.  The process starts, but nothing runs, looks asleep in Task Manager.
> Not worth messing around with, as its a minor issue.
>
>
>
> I toyed with using SW_SHOWINACTIVE and getting the program (Program B) to
> minimise itself on start, but that is just damned complicated and
> fiddly/fragile.  It also seems prone to ending up with 2 icons on the task
> bar, as though multiple copies have started even if only one is running –
> (maybe due to the large amount of work it does on startup – it is
> unresponsive for a good while) .
>
>
>
> I also tried Russells suggestion about setting the foreground window and
> it don’t work for me (Windows 8.1)
>
>
>
> What I did in the end was go back to the SW_SHOWMINIMIZED and then after
> the ShellExecute (in Program A) I put a ShowMessage saying I had started
> the other program.   Because this gives a modal clue that they have to
> click on to continue it will do the job of setting the focus back.  And its
> a bit useful for them to be informed it has been started.
>
>
>
>
>
> *From:* Jolyon Smith <jsmith at deltics.co.nz>
>
> *Sent:* Thursday, July 24, 2014 8:21 PM
>
> *To:* Russell Belding <russell at belding.co.nz> ; NZ Borland Developers
> Group - Delphi List <delphi at listserver.123.net.nz>
>
> *Subject:* Re: [DUG] Shellexecute question
>
>
>
> Have you tried passing *SW_SHOWMINNOACTIVE instead of SW_MINIMIZED ?*
>
>
>
> Caveat:  The show flag parameter is merely passed to the application being
> executed.  What it chooses to do with that flag is it's own affair, but if
> you're lucky, it will respect your wishes.  If not, then you will have to
> engage in a focus window arms race/lotto as already suggested.  But Route
> #1 would be to try the officially mandated mechanisms.
>
> Good luck.  :)
>
>
>
> On 24 July 2014 19:46, russell <russell at belding.co.nz> wrote:
>
> Tyr this after spawning the other program.
>
>
>
> SetForegroundWindow(forms.application.mainWindow.handle)
>
>
>
> To give the main window of your program focus.
>
> Perhaps modifications of this will take you to the window of the calling
> program where you want the focus?
>
>
>
> Russell
>
>
>
> *From:* delphi-bounces at listserver.123.net.nz [mailto:
> delphi-bounces at listserver.123.net.nz] *On Behalf Of *John Bird
> *Sent:* Thursday, 24 July 2014 4:43 p.m.
> *To:* NZ Borland Developers Group - Delphi List
> *Subject:* [DUG] Shellexecute question
>
>
>
> I have a program (Program A) that fires up another (program B)  via
> ShellExecute, if its not already running.  However even though Program B is
> started minimised, focus shifts away from Program A, which is a minor
> nuisance.
>
>
>
> Is there any way to stop this within Delphi?  Or will I have to do
> something like delve into the Windows API?
>
>
>
> if ShellExecute(Application.Mainform.Handle, 'open', Pchar(aProgName),
> PChar(aparaml), PChar(aDir), SW_SHOWMINIMIZED) <= 32 then
>
>   ShowMessage('Start Minimised error:')
>
>
>
>
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