Function slint_interpreter_component_instance_set_callback 

#[unsafe(no_mangle)]
pub unsafe extern "C" fn slint_interpreter_component_instance_set_callback(
    inst: &ErasedItemTreeBox,
    name: Slice<'_, u8>,
    callback: extern "C" fn(user_data: *mut c_void, arg: Slice<'_, Box<Value>>) -> Box<Value>,
    user_data: *mut c_void,
    drop_user_data: Option<extern "C" fn(*mut c_void)>,
) -> bool

Available on crate feature ffi only.

Set a handler for the callback. The callback function must initialize the ret (the ret passed to the callback is initialized and is assumed initialized after the function)