How can I control a ProgressIndicator value from Rust

[bob-anderson-ok]

I have an image that I compute and display in an Slint Image widget through a pure callback called render_image(...) -> Image:

Image {
    ... various properties
    source: render_image(refresh-image, ... );  // This does the heavy lifting.
}

This works well as I can trigger a call to render_image with a simple refresh-image += 1 in response to widget clicks or edits.

My problem is that sometimes the image calculation can be lengthy and I want to use a ProgressIndicator to inform the user as to what's going on. But I do not know how to change a widget property (ProgressIndicator value) from the rust side outside of a callback. It seems a violation of the reactive principals that Slint is based on and that may be why I cannot find an example. I'm guessing that I somehow need to interact with the Slint event queue, but I cannot find any example that I can understand that follows this path.

I'm looking for some threads to pull on.

[hunger]

You can define a image-load-progress in property in your root Element (or a global) and set this value from rust.

Then you can two-way bind this value to the progress indicator's value.

[bob-anderson-ok]

What does the Rust side look like? Bob

…

On Mon, May 19, 2025 at 1:31 AM Tobias Hunger ***@***.***> wrote: You can define a image-load-progress in property in your root Element (or a global) and set this value from rust. Then you can two-way bind this value to the progress indicator's value. — Reply to this email directly, view it on GitHub <#8466 (comment)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABG6OD3WZE7A3AULKTC4NI327GJGZAVCNFSM6AAAAAB5MIT53WVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTGMJZGA4DCOA> . You are receiving this because you authored the thread.Message ID: ***@***.***>

[hunger]

It depends on whether you define the property on the Window or a global object:

export component MainWindow {
    in-out property <int> image-load-progress-value: 0;

    [...]
    ProgressBar {
        value <=> root.image-load-progress-value;
    }
}

// create the UI:
let ui = MainWindow::new()?;

[...]

ui.set_image_load_progress_value(0);

[bob-anderson-ok]

The function that needs to update the progress indicator is defined outside of main (of course). But ui is defined inside of main. What is a good way to make ui visible to that external function? I am not averse to using static and unsafe as my app is single threaded. Bob

…

On Mon, May 19, 2025 at 9:21 AM Tobias Hunger ***@***.***> wrote: It depends on whether you define the property on the Window or a global object: export component MainWindow { in-out property <int> image-load-progress-value: 0; [...] ProgressBar { value <=> root.image-load-progress-value; } } // create the UI:let ui = MainWindow::new()?; [...] ui.set_image_load_progress_value(0); — Reply to this email directly, view it on GitHub <#8466 (reply in thread)>, or unsubscribe <https://github.com/notifications/unsubscribe-auth/ABG6OD2HICJJZBPFGANYRB327IAG5AVCNFSM6AAAAAB5MIT53WVHI2DSMVQWIX3LMV43URDJONRXK43TNFXW4Q3PNVWWK3TUHMYTGMJZGYYDMNY> . You are receiving this because you authored the thread.Message ID: ***@***.***>