Slider change event doesn’t fire when slider value set

[dougcooper]

I'm trying to change the value of a slider programmatically but the slider change event doesn't fire when I do, nor does the ui update. The underlying value does change. I have a property bound to the slider change event that I'm using in the rust side to get/set the slider value.

[hunger]

You set the value from Rust? Did you trigger the event loop after setting the value?

[dougcooper]

i did trigger the event loop. everything else works as expected. for instance if i manually drag the slider the event fires but when setting the slider value from rust it does not.

[hunger]

I mean did you trigger the event loop after setting the value from Rust?

Try doing

let _ = slint_interpreter::invoke_from_event_loop(|| {}); // wake event loop

after setting the value(s) from within rust to let Slint know that its time to go and update things.

[dougcooper]

I tried the code as your wrote it but it did not affect the outcome. Perhaps I need to set the value instead the closure?

[dougcooper]

This is how I invoked setting the slider value.

[ogoffart]

Indeed, the slider changed callback will only be called if the value is set by the user. Programmatically changing the value will not result in this being called.

However, the UI should refresh. If it doesn't that's a bug.
Do you have an example of code that show the problem?

[dougcooper]

example: https://github.com/dougcooper/slint-slider-test.git

[dougcooper]

@ogoffart i had a chance to play with a few other ui frameworks this week and i now have a better understanding of why you wouldnt fire a callback when the slider value changes programmatically. I think ultimately what i wanted to see is draw/render time when the slider changes positions as this appears to be an expensive operation elsewhere. With that said the UI still does not update when the slider value is set as least in my program. i think im doing it right.

[ogoffart]

I looked at your code code, and saw this:

https://github.com/dougcooper/slint-slider-test/blob/88a7fc28154b5855dd24830f9d9925e37b0a1e24/src/main.rs#LL9C33-L9C45

in-out property <float> slider-value: slider.value ;

But the : slider.value is a binding that is only working one way.
This is the same as saying let mut foobar = foo.bar.clone(); then changing foobar doesn't change the original value.

The fix is to do

in-out property <float> slider-value <=> slider.value ;

Which then does a two way binding, so changing slider-value also affect slider.value. and then the example works.

[dougcooper]

i really appreciate you looking at that. works great. is there a use case where you would want to say a property is an in type but not have it bind to the value?

[ogoffart]

is there a use case where you would want to say a property is an in type but not have it bind to the value?

To give a default value.