How to call a function after screen is displayed. BUG on LV_EVENT_SCREEN_LOADED?

How-to
1

Description

Hello everyone, and thank you in advance for any responses! :blush:

I’m encountering an issue where I want to call a function immediately after a screen is displayed. I’ve discovered the LV_EVENT_SCREEN_LOADED event, which seems to fit the bill.

Here’s what I’ve done so far: I’ve added this event to the screen I want to call the function after it’s loaded (ui_Screen2). Then, in the function (ui_event_Screen2), I’ve placed the code for the function I want to execute.

However, the problem I’m facing is that the function gets called not only when the screen is initially loaded (which is correct) but also when I navigate away from this screen to a new one.

Can anyone advise on how I can achieve the desired behavior? What might I be doing wrong, or what aspect of this mechanism have I misunderstood?

Thank you once again for your assistance!

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

ESP32-S3

What LVGL version are you using?

8.3.11

What do you want to achieve?

Call the function ui_event_Screen2 only on screen load.

What have you tried so far?

I have tryied to disable the second execution with a boolean variable but it let me crash the system.
If I comment the lv_scr_load_anim the function is correctly called once.

Code to reproduce

Not provided

Screenshot and/or video

Images to explain better.

The Screen1 rapresent in the first part the function called on setup whic append the function ui_event_Screen2 to the LV_EVENT_SCREEN_LOADED event. In the second part there’s the function that is called twice.

Screen1

image


The Screen2 rapresent the SerialMonitor used for debugging.
I have added a random number generate from the function to help identify the order of what is called and i have placed a Serial.println to replace my function call.

Screen2

image

2

Sorry, but call delay 1000 or any delay inside code is nonsense.
And good practice is place if check inside cb. Somethiink as

    lv_event_code_t event_code = lv_event_get_code(e);
    lv_obj_t * target = lv_event_get_target(e);
    if(event_code == LV_EVENT_SCREEN_LOADED) {

PS Seems your code is maybe from Squareline, then yuo all this can generate inside events designer.
3

Hi Marian,

The delay(1000) call was only for debugging purposes to illustrate what was happening within the code over time. Anyway thanks.

Regarding the event_code, it consistently remains LV_EVENT_SCREEN_LOADED because I’ve bound the invocation of ui_event_Screen2 only to that event, as indicated in the code snippet provided earlier.

Even with the inclusion of the if condition, the behavior remains unchanged. I’ve given it a try, but unfortunately, it doesn’t alter the outcome.

4

Then check if you dont have this twice in code. SQS place same func inside ui_init… I preffer search all files for lv_obj_add_event_cb

5

Already done.
I have placed for debugging purpose a Serial.print before the lv_obj_add_event_cb and it is called only once.
Already search for lv_obj_add_event_cb but there’s only one time with the binding of this function.
It seems that (as log show) the event LV_EVENT_SCREEN_LOADED be called twice, first when the screen is loaded (correctly) and the second when the animation to exit the screen is started (not expected).

If i comment the line of lv_obj_add_event_cb the function is never called, so it is binded only once and in that point.

6

Then maybe anim load screen invoke second loaded, im not sure i use 8.3.7 and SQS invoke method where is

void ui_event_Screen0(lv_event_t * e)
{
    lv_event_code_t event_code = lv_event_get_code(e);
    lv_obj_t * target = lv_event_get_target(e);
    if(event_code == LV_EVENT_SCREEN_LOADED) {
        _ui_screen_change(&ui_Screen1, LV_SCR_LOAD_ANIM_FADE_ON, 1200, 0, &ui_Screen1_screen_init);
    }
}
7

I’ve attempted to switch to version 8.3.7, and it appears that the issue of the function being called twice has been resolved. It seems there might be a bug specific in version 8.3.11.

Marian, could you please try temporarily switching to version 8.3.11 to confirm whether you encounter the same issue? You can do this by placing a Serial.print statement inside the ui_event_Screen0 function and checking if it appears twice.

If we can both confirm the double calling behavior in version 8.3.11, it would be great to open a bug report to address this issue.

Thank you for your cooperation.