Referencing to UI on C++

[metehus]

Hello! I'm trying to call a set function of the ui, but ouside my main function, on a callback. How do i do this?
For context, I'm using slint on the esp-idf framework. What i've tried is something like this:

static knob_handle_t knob;
slint::ComponentHandle<MainWindow>* ui_ptr;

// callback function to update count property
void input_cb (void *arg, void *data) {
    auto v = iot_knob_get_count_value(knob);
    printf("encoder value: %d\n", v);
    (*ui_ptr)->set_count(v);
};

extern "C" void app_main(void)
{
    // setup slint, knob, etc

    auto ui = MainWindow::create();

    ui_ptr = &ui;

    ESP_ERROR_CHECK(iot_knob_register_cb(knob, KNOB_LEFT, input_cb, NULL));
    ESP_ERROR_CHECK(iot_knob_register_cb(knob, KNOB_RIGHT, input_cb, NULL));

    // test set count
    (*ui_ptr)->set_count(20);

    uih->run();
}

When running, the count property is updated to 20, as I can see on the text component. But when the knob callback is triggered, i can see the "encoder value: %d" log being printed out with the right value, but the ui is not changed

[ogoffart]

Here is a suggestion:

static knob_handle_t knob;
// Use of std::optional as a static.
static std::optional<slint::ComponentHandle<MainWindow>> ui;

// callback function to update count property
void input_cb (void *arg, void *data) {
    auto v = iot_knob_get_count_value(knob);
    printf("encoder value: %d\n", v);
    (*ui)->set_count(v);

    // But I'm afraid the previous line will be problematic, depending how input_cb is called.
    // Because if it is in a different task, you need to use invoke_from_event_loop like so:
    slint::invoke_from_event_loop([v]{ (*ui)->set_count(v); })
};

extern "C" void app_main(void)
{
    // setup slint, knob, etc

    // assign dirrectly to the optional.
    ui = MainWindow::create();

    ESP_ERROR_CHECK(iot_knob_register_cb(knob, KNOB_LEFT, input_cb, NULL));
    ESP_ERROR_CHECK(iot_knob_register_cb(knob, KNOB_RIGHT, input_cb, NULL));

    // test set count
    (*ui)->set_count(20);

    (*ui)->run();
}

(I did not test this code.)