slint-ui/slint · error

Cannot get property

Error message

Cannot get property {global_name}::{name}: {e}

What it means

LiveComponent::get_global_property panics when the interpreter cannot read the requested property from the named global singleton. Since the return type is Value (not Result), an unresolvable global/property or type conversion error has no representation other than a panic.

Solutions

1. Confirm the global is exported and the property is declared (and public) on it
2. Ensure the LiveComponent compiled and instantiated successfully before reading globals
3. Re-read after hot-reload only with names still present in the new .slint version

Example fix

// before
let v = live.get_global_property("Theme", "accent"); // global renamed to Palette
// after
let v = live.get_global_property("Palette", "accent");

let known_globals: Vec<_> = instance.definition().globals().iter().map(|g| g.name.clone()).collect();
debug_assert!(known_globals.iter().any(|g| g == "Palette"));

// panic! is not catchable; ensure the instance compiled and the global exists first
assert!(instance.definition().globals().iter().any(|g| g.name == "Palette"));
let v = live.get_global_property("Palette", "accent");

When it happens

Trigger: get_global_property with a global name not exported from the component, a property name missing on that global, or when the compiled instance was reloaded and globals were renamed.

Common situations: Reading a property before the component instance was successfully created; typos in global or property names; assuming a global exists that the designer removed from the .slint file.

Understand the failure class

Background: "Not found" and "does not exist" errors: why "Task not found", "No such folder", and "Can't find" fire when a lookup comes back empty — this error's family across 14 libraries.

Related errors

• Cannot invoke callback
• Cannot set callback
• Cannot set property
• Global was just valid
• root_component() called on a definition built without…

AI-assisted analysis of slint-ui/slint@3a7e700487 (2026-09-16). Data as JSON: /api/errors/07456fcc5ed43700. Report an issue: GitHub.

Appendix: source

Thrown at internal/live-preview/live_component.rs:224

        self.callbacks.borrow_mut().insert(name.into(), callback.clone());
        self.instance()
            .set_callback(name, move |args| callback(args))
            .unwrap_or_else(|e| panic!("Cannot set callback {name}: {e}"));
    }

    /// forward to set_global_property
    pub fn set_global_property(&self, global_name: &str, name: &str, value: Value) {
        self.properties.borrow_mut().insert(format!("{global_name}.{name}"), value.clone());
        self.instance()
            .set_global_property(global_name, name, value)
            .unwrap_or_else(|e| panic!("Cannot set property {global_name}::{name}: {e}"))
    }

    /// forward to get_global_property
    pub fn get_global_property(&self, global_name: &str, name: &str) -> Value {
        self.instance()
            .get_global_property(global_name, name)
            .unwrap_or_else(|e| panic!("Cannot get property {global_name}::{name}: {e}"))
    }

    /// Forward to invoke_global
    pub fn invoke_global(&self, global_name: &str, name: &str, args: &[Value]) -> Value {
        self.instance()
            .invoke_global(global_name, name, args)
            .unwrap_or_else(|e| panic!("Cannot invoke callback {global_name}::{name}: {e}"))
    }

    /// Forward to set_global_callback
    pub fn set_global_callback(
        &self,
        global_name: &str,
        name: &str,
        callback: Rc<dyn Fn(&[Value]) -> Value + 'static>,
    ) {
        self.callbacks.borrow_mut().insert(format!("{global_name}.{name}"), callback.clone());
        self.instance()

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