Lv_event_get_user_data - pass and receive a string from "lv_obj_add_event_cb"

How-to
1

Hi guys

Parameters:
LVGL 8.3.10
Arduino IDE 2.2.1 Linux
ESP32

I’m trying to pass a string information from “lv_obj_add_event_cb” and to receive the same value inside “lv_event_get_user_data” but it’s bringing me an invalid character value.
image

First function:

char * wifiName;
wifiName = "abc";
Serial.print("I'll send: ");
Serial.println(wifiName);
network = lv_list_add_btn(list1, LV_SYMBOL_WIFI, wifiNameA.c_str());
lv_obj_add_event_cb(network, list_event_handler, LV_EVENT_CLICKED, &wifiName);

image

Second function:

static void list_event_handler(lv_event_t * e)
{
    lv_event_code_t code = lv_event_get_code(e);
    lv_obj_t * obj = lv_event_get_target(e);

   char * userdata = (char*)lv_event_get_user_data(e);
   
   // char * vai = (char*)lv_obj_get_user_data(e);
    Serial.print("I recieved: ");
    Serial.println((char*)lv_event_get_user_data(e));
    Serial.println((char*)userdata);

    if(code == LV_EVENT_CLICKED) {
        lv_example_textarea_2();
    }
}

image

What I’m doing wrong here?

Thank so much

Best Regards

2

Sho code where and how you declare wifiName

3

HI @mmar22

I updated the first post…

Thank so much

4

is complete bad in C maybe in C++ ok assign cont string, but as local cant be used in cb func as user data. Create it global and for safe

char wifiname[10];
5

Hi @Marian_M
Thank so much… Almost solved. I can pass the information, but only works for last item of list.
Can you please help me to understand my fault?


static void list_event_handler(lv_event_t * e)
{
  lv_event_code_t code = lv_event_get_code(e);
  lv_obj_t * obj = lv_event_get_target(e);

  const char *userdata = (char*)lv_event_get_user_data(e);

  Serial.print("I recieved: ");
  Serial.println(userdata);

  if(code == LV_EVENT_CLICKED) {
      lv_example_textarea_2();
  }
}

void scan_wifi(){

  lv_obj_t * list1;
  list1 = lv_list_create(tab3);
  lv_obj_set_size(list1, 180, 220);
  lv_obj_center(list1);

  String wifiNameAndSignal = "";
  char *wifiName[0];

  int n = WiFi.scanNetworks();
  Serial.println("scan done");

  if (n == 0) {
      Serial.println("no networks found");
      lv_list_add_text(list1, "No Networks found :(");
  } else {
    Serial.print(n);
    Serial.println(" networks found");
    lv_list_add_text(list1, "Networks found:");

    for (int i = 0; i < n; ++i) {

      *wifiName = {};
      wifiNameAndSignal = WiFi.SSID(i) + " (" + WiFi.RSSI(i) + " db)";

      String wifiNameOnly = WiFi.SSID(i);
      *wifiName = (char*)wifiNameOnly.c_str();
      Serial.print("I'll send: ");
      Serial.println(*wifiName);

      network = lv_list_add_btn(list1, LV_SYMBOL_WIFI, wifiNameAndSignal.c_str());
      lv_obj_add_event_cb(network, list_event_handler, LV_EVENT_CLICKED, *wifiName);

      String LabelItem = (String)(i+1) + ": " + WiFi.SSID(i) + " (" + WiFi.RSSI(i) + "db)";
             LabelItem += (WiFi.encryptionType(i) == WIFI_AUTH_OPEN)?" ":"*";
      Serial.println(LabelItem);
      Serial.println("-------------------------------------------------------------------------------");
      delay(10);
    }
  }
  Serial.println("");
}

The Serial Monitor info:

scan done
11 Networks found
I'll send: NET0001
1: NET0001 (-52db)*
-------------------------------------------------------------------------------
I'll send: NET0002
2: NET0002 (-56db)*
-------------------------------------------------------------------------------
I'll send: NET0003
3: NET0003 (-57db)*
-------------------------------------------------------------------------------
I'll send: NET0004
4: NET0004 (-59db)*
-------------------------------------------------------------------------------
I'll send: NET0005
5: NET0005 (-61db)*
-------------------------------------------------------------------------------
I'll send: NET0006
6: NET0006 (-75db)*
-------------------------------------------------------------------------------
I'll send: NET0007
7: NET0007 (-76db)*
-------------------------------------------------------------------------------
I'll send: NET0008
8: NET0008 (-83db)*
-------------------------------------------------------------------------------
I'll send: NET0009
9: NET0009 (-84db)*
-------------------------------------------------------------------------------
I'll send: NET00010
10: NET00010 (-84db)*
-------------------------------------------------------------------------------
I'll send: DIRECT-8B-HP ENVY 7640 series
11: DIRECT-8B-HP ENVY 7640 series (-87db)*
-------------------------------------------------------------------------------

I recieved: ����������?$9�?\��?
I recieved: ����������?$9�?\��?
I recieved: DIRECT-8B-HP ENVY 7640 series
I recieved: ����������?$9�?\��?

Thank so much

Best Regards

6

Still you mix chaos of C++ and C. But primary mistake is you create one wifiname pointer and many buttons with callbacks to one name, then result is last one name for all clicks.

7

THank so much

I 'll try to fix the languages here.

Best Regards

8

and you still place this inside func = local variable , that stop exist on func end. Then you cant use it in cb userdata.