How do I force a refresh to take place immediately ?

[gabrielfougeron]

A button click starts a long (a few seconds) computation. I'd like to show some kind of "Please wait" message during the computation, and then reset.
However, when I do the following:

    @on(Button.Pressed, "#LongComputationButton")
    def action_start_long_computation(self):

          lbl = self.query_one("#LongComputationLabel")  
          lbl.content = "Please wait"
          
          do_long_computation()

          lbl.content = "Computation finished"

The label only refreshes once, after the computation is complete.
How can I get the label to refresh twice, once before the call to do_long_computation(), and once after ?

[willmcgugan]

The UI will update when the message handler finishes, which is why you are seeing this.

The solution is to make the handler a worker so it runs concurrently. And perform your long computation in a thread so it doesn't stall the event loop. Something like this:

    @on(Button.Pressed, "#LongComputationButton")
    @work
    async def action_start_long_computation(self):

          lbl = self.query_one("#LongComputationLabel")  
          lbl.content = "Please wait"
          
          await asyncio.to_thread(do_long_computation)

          lbl.content = "Computation finished"

[gabrielfougeron]

OMG thanks for the super quick reply. This works perfectly. I guess you can tell I'm not used to async computation ^^

[gabrielfougeron]

I'm getting a weird behavior after this change though. After I quit the app, I'm getting the following error:

Tcl_AsyncDelete: async handler deleted by the wrong thread
Aborted (core dumped)

Any idea what's going on?

[willmcgugan]

That doesn't look like anything Textual related. Are you using tkinter ?

[gabrielfougeron]

As a matter of fact, I am. Could this be a tkinter issue you have encoutered in the past ?

[willmcgugan]

The "tcl" gave it away. I'm not sure what that error means I'm afraid. You may have to research that.

If you are launching a gui window, you might have better results using a subprocess.

[gabrielfougeron]

Thanks fot all the tips :-)

[gabrielfougeron]

After a few tests, the function call_after_refresh seems to behave as I expect, and I was able to get the desired behavior. Is this considered bad habit ?