Send recolor code via lv_obj_add_event_cb

How-to
,
1

How properly send text with recolor code via lv_obj_add_event_cb message

What MCU/Processor/Board and compiler are you using? ESP32-S3 on PlatformIO

What LVGL version are you using? 8.3.0 dev

What do you want to achieve? Recolor part of text send via lv_obj_add_event_cb message

What have you tried so far?

I am beginner in C / C++ programing but have experience in other languages Lisp, VBA, Pascal. That’s why I a bit confused with all those types / references etc.

I have simple code which is based on some events like pushbutton, and should change something. For this exercise I want to recolor only integer value of concatenated text: Volume: #ff0000 18# or Volume: #00ff00 7# or Volume: Muted (when level is == 0)
Sending result to Serial.print gives expected results as above, but when using function it result with ? or H? rubbish on the screen. Only Volume: Muted pass OK as this is purely string.
How to properly pass those #ff0000# and other color codes.

Code to reproduce

    String color_code;
    cur_volume++;
    cur_volume = cur_volume % 21; // 0...21
    color_code = "Volume: "; // prefix
    if (cur_volume == 0) {
      color_code += "Muted"; // plain white
    } else if (cur_volume > 0 and cur_volume < 15) {
      color_code += "#00ff00 "; // green
      color_code += cur_volume;
      color_code += "#";
    } else {
      color_code += "#ff0000 "; // red
      color_code += cur_volume;
      color_code += "#";
    }
    Serial.print("Color Code: ");
    Serial.println(color_code);
    lv_msg_send(MSG_NEW_VOLUME, &color_code);

Result in terminal:
Color Code: Volume: #ff0000 20#
Color Code: Volume: Muted
Color Code: Volume: #00ff00 1#

  lv_obj_t *volume_label = lv_label_create(tileView);
  lv_obj_align_to(volume_label, bat_label, LV_ALIGN_OUT_BOTTOM_LEFT, 0, 5); //align to other element on screen
  lv_label_set_recolor(volume_label, true); 
  lv_label_set_text(volume_label, "Volume: #00ff00 10#"); // default value works too
  lv_obj_add_event_cb(volume_label, update_text_subscriber_cb, LV_EVENT_MSG_RECEIVED, NULL);
  lv_msg_subsribe_obj(MSG_NEW_VOLUME, volume_label, (void *)"%s");


static void update_text_subscriber_cb(lv_event_t *e) {
  lv_obj_t *label = lv_event_get_target(e);
  lv_msg_t *m = lv_event_get_msg(e);

  const char *fmt = (const char *)lv_msg_get_user_data(m);
  const char *t = (const char *)lv_msg_get_payload(m);

  lv_label_set_text_fmt(label, fmt, t);
}

Where I am doing error?
Thanks

2

Hmm, I think the problem is, that you have to convert cur_volume to a String first, and then concatenate it.
Maybe putting it into String (cur_volume) will help, e.g.:

      color_code += "#00ff00 "; // green
      color_code += String (cur_volume);
      color_code += "#";

See String

3

Nope. This is not good.
I have figured solution, but not sure if that is correct or fast way etc.
Changed type to char and sprintf

char color_code[20];

sprintf(color_code, "Volume: #ff0000 %d#", cur_volume);

If it works, then do not change, but improvements are welcome.

4

Be careful with sprintf!
Currently your buffer is large enough to hold that string with decimal values up to 99.
Better use snprintf.
If you need string/char functions in C try to use all the function with the ‘n’, e.g. strncat, strncpy…
Many problems in C programming come from buffer overflow! And the C-String functions (without the ‘n’) are predestined for it.

5

Thanks. Luckily cur_volume can be only in range 0-21 in my case, but suggestion noted.