How do I get Simple Meter (lv_example_meter_1) to work in my Lvgl code

How-to
1

Description

I am trying to get the Simple Meter example (lv_example_meter_1) to work.

In this line:-

 lv_meter_set_indicator_value(meter, indic, v);

I get the error;
argument of type “void *” is incompatible with parameter of type “lv_meter_indicator_t *”

What MCU/Processor/Board and compiler are you using?

ESP32S3

What LVGL version are you using?

8.3.9

What do you want to achieve?

Get this example to work in my already working Lvgl code.

I already have a meter being updated with a DHT22 temperature sensor via painlessMESH.
I am now trying to get the callback function working.

What have you tried so far?

I have moved the set_value_cb procedure around but it is still complaining

Code to reproduce

//static lv_obj_t * meter;

static void set_value_cb(void * indic, int32_t v)
{
    lv_meter_set_indicator_value(meter, indic, v);
}

/**
 * A simple meter
 */
void lv_example_meter_1(void)
{
    meter = lv_meter_create(lv_scr_act());
    lv_obj_center(meter);
    lv_obj_set_size(meter, 200, 200);

    /*Add a scale first*/
    lv_meter_scale_t * scale = lv_meter_add_scale(meter);
    lv_meter_set_scale_ticks(meter, scale, 41, 2, 10, lv_palette_main(LV_PALETTE_GREY));
    lv_meter_set_scale_major_ticks(meter, scale, 8, 4, 15, lv_color_black(), 10);

    lv_meter_indicator_t * indic;

    /*Add a blue arc to the start*/
    indic = lv_meter_add_arc(meter, scale, 3, lv_palette_main(LV_PALETTE_BLUE), 0);
    lv_meter_set_indicator_start_value(meter, indic, 0);
    lv_meter_set_indicator_end_value(meter, indic, 20);

    /*Make the tick lines blue at the start of the scale*/
    indic = lv_meter_add_scale_lines(meter, scale, lv_palette_main(LV_PALETTE_BLUE), lv_palette_main(LV_PALETTE_BLUE),
                                     false, 0);
    lv_meter_set_indicator_start_value(meter, indic, 0);
    lv_meter_set_indicator_end_value(meter, indic, 20);

    /*Add a red arc to the end*/
    indic = lv_meter_add_arc(meter, scale, 3, lv_palette_main(LV_PALETTE_RED), 0);
    lv_meter_set_indicator_start_value(meter, indic, 80);
    lv_meter_set_indicator_end_value(meter, indic, 100);

    /*Make the tick lines red at the end of the scale*/
    indic = lv_meter_add_scale_lines(meter, scale, lv_palette_main(LV_PALETTE_RED), lv_palette_main(LV_PALETTE_RED), false,
                                     0);
    lv_meter_set_indicator_start_value(meter, indic, 80);
    lv_meter_set_indicator_end_value(meter, indic, 100);

    /*Add a needle line indicator*/
    indic = lv_meter_add_needle_line(meter, scale, 4, lv_palette_main(LV_PALETTE_GREY), -10);

    /*Create an animation to set the value*/
    lv_anim_t a;
    lv_anim_init(&a);
    lv_anim_set_exec_cb(&a, set_value_cb);
    lv_anim_set_var(&a, indic);
    lv_anim_set_values(&a, 0, 100);
    lv_anim_set_time(&a, 2000);
    lv_anim_set_repeat_delay(&a, 100);
    lv_anim_set_playback_time(&a, 500);
    lv_anim_set_playback_delay(&a, 100);
    lv_anim_set_repeat_count(&a, LV_ANIM_REPEAT_INFINITE);
    lv_anim_start(&a);
}

Screenshot and/or video

If possible, add screenshots and/or videos about the current state.
Screen_Shot

1 Like
2

I’m having the exact same problem with v8.3. I tried casting ‘indic’ with (lv_meter_indicator_t *) it compiles but does not work (it keeps flashing the screen) :frowning:

3

Same issue here. Will not build in platformio and throws this error message:
argument of type "void *" is incompatible with parameter of type "lv_meter_indicator_t *"

4

I think this turns out to be a name mangling issue. Here is how I solved it.

First, I created myWidgets.h and myWidgets.c in my src directory

I put the contents of lgvl\src\examples\widgets\meter\lv_example_meter_1.c into myWidget.c

myWidgets.c

#include "myWidgets.h"

static lv_obj_t * meter;

static void set_value(void * indic, int32_t v)
{
    lv_meter_set_indicator_value(meter, indic, v);
}

void my_example_meter_1(void)
{
    // https://docs.lvgl.io/8.0/widgets/extra/meter.html
    
    meter = lv_meter_create(lv_scr_act());
    lv_obj_center(meter);
    lv_obj_set_size(meter, 200, 200);
blah, blah, blah ...
}

And the key now is the myWidgets.h where we extern “C”

#ifndef _MY_WIDGETS_H_
#define _MY_WIDGETS_H_

#include <lvgl.h>

#ifdef __cplusplus
extern "C" {
#endif

void my_example_meter_1(void);

#ifdef __cplusplus
} /*extern "C"*/
#endif

#endif // _MY_WIDGETS_H_

And in your main.cpp DO NOT include “examples/lv_examples.h” or
“demos/lv_demos.h” but do include “myWidgets.h”

5

Thanks PeteDD. I will look into this.

6

Try to cast as lv_obj_t

void lv_meter_set_indicator_value(lv_obj_t *obj, lv_meter_indicator_t *indic, int32_t value)