How to detect when a button is pressed/released/toggled, not just clicked

[drewlwhitney]

Hello! Love Slint, this project is awesome.

When working with a basic Button, I know it has the clicked signal. Are there equivalent pressed and released signals?

My use case is controlling a motor. When I press the button, I want the motor to be on for as long as the button is held. When the button is released, I want to stop the motor. I just don't know how to separately detect press and release events.

Additionally, is there an easy way to detect when a button has been toggled if it is checkable, i.e. a toggled signal, or do you have to check on an interval?

Thanks!

[Vadoola]

I can't say for certain, because I've never tried, I think you would need to create your own custom button to do that.

Here is a quick thrown together example showing a rough idea of handling the down and up events on a touch area for a custom "button". It's not exactly what you want, but hopefully will lead you in the right direction.

In regards to reacting to if the button has been toggled, haven't tested this, but perhaps add in a changed callback for the buttons state?: https://slint.dev/blog/property-changed-callback

[drewlwhitney]

Oooo this is perfect.

For the press/release example, is there a way to create and trigger a custom signal when the button is pressed/released? Otherwise, it seems like I could have pressed and released properties, update them, and detect when they change via a property-changed-callback.

The property-changed-callback system is ingenious, that's a perfect solution for toggle detection.

Thanks for getting back to me so quickly!

[Vadoola]

it sounds like what you might want is a custom callback.

You could have multiple callbacks, and call them depending on the situation. Such as button pressed call callback1, button released call callback2. The callbacks would be handled in code (Rust, C++, etc), a quickly modified example would be like this.

You could also do a single callback with a parameter. An example of this is in Tomotroid for the start button. I essentially create a custom button that acts as a start/stop, and passes an enum to a single callback. When the Touch Area is clicked if the state shows it's currently running, it triggers action-timer(TimerAction.stop), otherwise it triggers action-timer(TimerAction.start). Of course you could update this to change based on pressed and released events instead of clicked, but basic principle is the same.

Then the rust code, determines what to do and change the state appropriately.

I don't know what your situation/project is exactly, but on screen jog controls have some other considerations you probably need to consider. What happens if say your application / computer running the program crashes while the button is held down? The release command never gets called, does your motor just keep running unless you pull the power somehow? Just something that needs to be considered. There are options for handling these situations, but I don't really know the details of what you are doing, so it's hard to say.

[drewlwhitney]

The callback system works perfectly! I'm coming from Qt so I'm used to their whole signal/slot system, but a combination of Slint callbacks and property-changed-callbacks should do the trick. The motors are tiny so you would have time to pull power before anything bad happened, but good point. Thank you so much for your help @Vadoola!