Description
What MCU/processor/board and compiler are you using?
DISCO-F746NG | Mbed with Mbed studio compiler.
What version of LVGL are you using?
8.3.4
What do you want to accomplish?
Good morning,
I want to successively display the examples included in the LVGL library. The major difficulty is to correctly release the resources between each example.
I would like to know if it is possible to erase all the screens created previously without knowing their numbers and identifiers?
Is there a function that would remove all inactive screens?
Is there a function that would allow to have the number of screens created? Or the number of objects that have no parent? I think it would be the same, it would allow using lv_obj_del().
What have you tried so far?
I saw that the lv_obj_clean() function allows to delete all the children of a screen (with the lv_scr_act() parameter for the active screen).
The lv_obj_del() and lv_obj_del_async() functions are used to delete a screen, except the active screen.
Marc.
Hello!
I think the best way is to have a handler for each screen and a structure that contains the elements for each one.
In my application I created a function responsible for initializing and deallocating the resources based on a variable that has the current and the old screen.
It is important to note that in this model each screen has a function that initializes its elements.
I will leave my code snippet for you to check.
/* ************************************************************
* PRIVATE TYPES DEFINITION *
* ***********************************************************/
/**
*
*/
typedef struct {
lv_obj_t *btnEnterBack;
lv_obj_t *btnUp;
lv_obj_t *btnDown;
} screenYourScreen1Itens_t;
/**
*
*/
typedef struct {
lv_obj_t *btnEnterBack;
lv_obj_t *btnUp;
lv_obj_t *btnDown;
} screenYourScreen2Itens_t;
/**
*
*/
typedef enum {
SCREEN_YOUR_SCREEN_1 = 0,
SCREEN_YOUR_SCREEN_2,
SCREEN_YOUR_SCREEN_3,
SCREEN_ENDINDEX,
SCREEN_INVALID_VALUE,
} screensList_e;
/**
*
*/
typedef struct {
lv_obj_t *btnEnterBack;
lv_obj_t *btnUp;
lv_obj_t *btnDown;
} screenYourScreen3Itens_t;
/* ************************************************************
* PRIVATE GLOBAL VARIABLES DEFINITION *
* ***********************************************************/
static lv_obj_t *scrYourScreen1 = NULL;
static screenYourScreen1Itens_t screenYourScreen1Itens;
static lv_obj_t *scrYourScreen2 = NULL;
static screenYourScreen2Itens_t screenYourScreen2Itens;
static lv_obj_t *scrYourScreen3 = NULL;
static screenYourScreen3Itens_t screenYourScreen3Itens;
static screensList_e m_oldScreen = SCREEN_INVALID_VALUE;
static screensList_e m_curScreen = SCREEN_INVALID_VALUE;
/* ************************************************************
* DEFINITION OF PRIVATE FUNCTIONS *
* ***********************************************************/
void scrYourScreen1Init(void) {
lv_obj_t *label;
screenYourScreen1Itens.btnEnterBack = lv_btn_create(scrYourScreen1);
lv_obj_align(screenYourScreen1Itens., LV_ALIGN_BOTTOM_LEFT, 0, 0);
label = lv_label_create(screenYourScreen1Itens.);
lv_label_set_text_fmt(label, "%s", "Test");
lv_obj_center(label);
lv_obj_set_size(screenYourScreen1Itens., lv_pct(33), lv_pct(16));
lv_obj_set_style_bg_color(screenYourScreen1Itens., lv_color_black(), LV_PART_MAIN);
lv_obj_set_style_text_color(label, lv_color_white(), 0);
}
/**
*
*/
static void navigateToScreen(screensList_e screenToGo) {
if(m_curScreen != screenToGo) {
switch (screenToGo) {
/**************************/
case SCREEN_YOUR_SCREEN_1:
scrYourScreen1Init();
lv_disp_load_scr(scrYourScreen1);
break;
/**************************/
case SCREEN_YOUR_SCREEN_2:
scrYourScreen2Init();
lv_disp_load_scr(scrYourScreen2);
break;
/**************************/
case SCREEN_YOUR_SCREEN_3:
scrYourScreen3Init();
lv_disp_load_scr(scrYourScreen3);
break;
/**************************/
default:
break;
/**************************/
}
m_oldScreen = m_curScreen;
m_curScreen = screenToGo;
switch (m_oldScreen) {
/**************************/
case SCREEN_YOUR_SCREEN_1:
lv_obj_del(scrYourScreen1);
break;
/**************************/
case SCREEN_YOUR_SCREEN_2:
// if you use a timer, can delete here lv_timer_del(timerHandler);
lv_obj_del(scrYourScreen2);
break;
/**************************/
case SCREEN_YOUR_SCREEN_3:
lv_obj_del(scrYourScreen3);
break;
/**************************/
default:
break;
}
}
}
// In your application you just need call the navigateToScreen() with properly screen like:
navigateToScreen(SCREEN_YOUR_SCREEN_1);```
Thank you for your answer.
Sorry to only answer now, I only just tried the code you posted. 
This code looks interesting, but I can’t get it to work, it looks like there are several errors in this code.
After looking at the Create screens part of this page: Objects — LVGL documentation I replaced the line:
static lv_obj_t * scrYourScreen1 = NULL;
by
static lv_obj_t * scrYourScreen1 = lv_obj_create(NULL);
But even this single line in my code causes my target to crash, despite what I read in the documentation. 
I call these libraries in my tests:
#include "mbed.h"
#include "lvgl.h"
#include "hal_stm_lvgl/tft/tft.h"
#include "hal_stm_lvgl/touchpad/touchpad.h"
We forgot the initializations:
lv_init(); //Initialize the LVGL
tft_init(); //Initialize display
touchpad_init(); //Initialize touchpad
after this this line works.
static lv_obj_t * scrYourScreen1 = lv_obj_create(NULL);
Yes, but I can’t put this line in the global declarations and put the init in the main() because they have to be called before.