Re: [Pythoncard-users] Pressing a button while the application is still in another event handler...

[Kevin A. <al...@se...>]

Alex provided some good info. The findfiles tool, hopalong, life, and 
spirograph samples all make use of SafeYield so I suggest taking a look 
at those for various ways of starting a long running process that 
doesn't involve using threads. I particularly like the use of a 
generator in the hopalong sample and just like the other samples 
mentioned above it handles starting a routine and allowing the user to 
stop the execution in a clean way. Other samples such as webgrabber, 
chat, jabberChat, webserver show how to use threads, but using threads 
is more complicated and error-prone and you probably don't need them.

ka
On Jul 9, 2004, at 8:39 AM, Alex Tweedly wrote:

> At 14:01 09/07/2004 +0200, pie...@ba... wrote:
>
>> Hello,
>>
>> I have the following problem:
>>
>> I'm writing a PythonCard application that has 2 buttons (a start 
>> button and
>> a stop button).
>>
>> When I press the start button, the 'on_cmdStart_mouseClick(self, 
>> event):'
>> function is executed.
>> Now, I want to be able to stop that function at any time by pressing 
>> the
>> STOP button.
>>
>> My problem is now that 'mouseClick'-events are not seen as long as 
>> I'm in
>> the 'on_cmdStart_...' function.
>>
>> Can anyone help me?
>
> It's not just mouse-Click events that aren't seen - while your code is 
> running, no events will be processed.
>
> You should read (or re-read to remind yourself) about
> http://pythoncard.sourceforge.net/timers-threads.html
>
> Note in particular the introductory paragraph that says:
>
>> Most of the top-level code you add to the front ends - your 
>> PythonCard user interfaces - is event handlers. As with programming 
>> with any GUI, event handlers should always complete their job fast, 
>> and return promptly, so they don't 'clog up the works'. PythonCard is 
>> no exception.
>
> While an event handler is running, no further events can happen. The 
> cleanest way to deal with processing that takes a long time is using 
> threads - and is well explained in that tutorial.
>
> If you have a really simple case, you can use the wxApp function Yield 
> - but read the cautions about its dangers - see the wx documentation 
> for wxApp::Yield
>
> Here's a simple bit of code that shows what this does
>
> Notes.
> 1. the work this does to keep it busy is calculate factorials - hey, 
> I've always wanted a chance to write a recursive factorial function 
> for a good purpose :-)
> 2. each time round the loop, it calls yield to allow other events to 
> be processed - without this the Stop button click wouldn't happen, and 
> in fact the writing and updating of the TextArea would happen.  (try 
> commenting out the Yield line to see it fail ....)
> 3. the "app" in "app.Yield()" is the global from the main program (not 
> included here, but the standard name used in the templates).
>
>
>     def on_openBackground(self, event):
>         self.results = []
>
>     def on_Start_mouseClick(self, event):
>         def fact(i):
>             if i<=1: return 1
>             return i * fact(i-1)
>
>         self.stopping = False
>         for i in range(1000):
>             j = fact(i)
>             s = "%d! is %d" % (i, j)
> ##            self.results.append(s)
> ##            self.components.TextArea1.text = "\n".join(self.results)
>             self.components.TextArea1.text = str(i)
>             app.Yield()
>             if self.stopping: break
>
>     def on_Stop_mouseClick(self, event):
>         self.stopping = True
>
>
> -- Alex.
>
>
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