On Nov 4, 2006, at 10:22 AM, Norman Palardy wrote:
It probably needs to yield to RB which I why I'd do a plugin
Given that I just have read the nug digest version, where the same
problem is discussed, I will repost what I had said previously and a
general solution to the problem:
If you are being called by a callback the natural instinct is to
respond immediately. And if it requires updating of a GUI, refreshing
windows, or a lengthy calculation, then it will interfere with
REALbasic's runtime. Basically, you are blocking the event loop if
you are going to issue a lot of stuff, while in the callback. So you
do not want to do this.
1: You want to return as quickly as possible from the callback
2: You should tell your RB code that you were called
3: You will deal with the callback after the callback was issued
An RB thread is not the solution, nor will DoEvents. DoEvents will
force the main event loop (the RB runtime) to cycle once. In both
cases you will be back into the callback, but meanwhile you told the
RB runtime to cycle, while that runtime does not know anything with
respect to the callback.
Here is code that is based on the above 3 rules.
Class CallEvent
properties:
next as CallEvent
myInstance as MyClass
signature as Integer
method:
CreateEvent(instance as MyClass)
dim theEvent, currentEvent As CallEvent
theEvent = me
theEvent.signature = 1000
theEvent.myInstance = instance
if EventModule.gEvent <> nil then
currentEvent = EventModule.gEvent
while currentEvent.nextEvent <> nil
currentEvent = currentEvent.nextEvent
Wend
currentEvent.nextEvent = theEvent
else
EventModule.gEvent = theEvent
end if
Module EventModule
properties:
gEvent As CallEvent
Class EventTimer as Timer
Action: // The Action event of the timer
SwallowEvent
Method:
SwallowEvent()
if EventModule.gEvent <> nil then
dim instance as MyClass
while EventModule.gEvent <> nil
dim curEvent As CallEvent = EventModule.gEvent
EventModule.gEvent = EventModule.gEvent.nextEvent
if curEvent.signature = 1000 then
instance = curEvent.myInstance
instance.myInstanceMethod// method of your class
end if
curEvent = nil
Wend
end if
Without going into details here, you call this
dim postEvent as new CallEvent
postEvent.CreateEvent()
in the callback. You have created an instance of a CallEvent which
will be handled in the main event. It is sufficient to only create
this instance and you will permanently leave the dylib's callback, as
it should. The timer will "sense" that there is an instance of
Callback and will issue the swallowing of the CallEvent. Since the
timer runs in the main event loop, the RBRuntime will handle your
code appropriately, and the dylib "runtime" is satisfied as well.
Hope this will clarify the general issue of returning from a callback
immediately, the posting of an event and the handling of the event in
the RB runtime.....
Alfred
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