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Back to article list Search Articles Add Comment Printer friendly Direct link Par2: Check for multiple instances of a program using DDE 1999-10-04 -- Richard Taylor 32-bit programs, unlike 16-bit programs, do not automatically default to a single running
instance. Users can easily initiate multiple program instances by just being a little
impatient and double-clicking the program icon twice. For some applications this is not
a problem, but for others it could be disastrous. Therefore, limiting Users to a single
running instance is necessary and actually pretty simple to accomplish. The trick here is
to make your program a DDE Server and have it look for an already running instance of
itself before fully loading.
You need to declare a global variable:
Channel LONG
And you need to prototype a Windows API call in the Inside the Global Map embed point:
MODULE('Windows API Call')
BringWindowToTop(LONG),BYTE,RAW,PASCAL,NAME('BringWindowToTop'),PROC
END
Then in the Program Setup embed point:
Channel = DDECLIENT('MYPROGRAM') !look for running instances of this program
IF Channel <> 0 ! and if found
DDEEXECUTE(Channel,'INFRONT') ! tell the running instance to take focus
DDECLOSE(Channel)
RETURN ! then get out
END
Then in the AppFrame's ThisWindow.Init method, after opening window embed point:
Channel = DDESERVER('MYPROGRAM') !set program as a DDE Server
Then in the AppFrame's ThisWindow.TakeEvent method, top of CYCLE/BREAK
support embed point:
IF EVENT() = Event:DDEexecute
IF DDEVALUE() = 'INFRONT' !tells it to bring itself to the front
AppFrame{PROP:Iconize} = FALSE
BringWindowToTop(AppFrame{PROP:Handle}) !and this does it
END
END
Today is May 2, 2024, 11:19 am This article has been viewed 35114 times.
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