Malloc, create several objects

How-to
1

Description

Is it possible to create several objects such as buttons dynamically via malloc?

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

Arduino Due (Cortex M3), Arduino IDE

What LVGL version are you using?

7.11

What have you tried so far?

Something like this:

static void dyn_create(lv_obj_t * parent)
{
  uint16_t size_dummy_label =30;

  
  lv_obj_t * dummy_text_label = lv_textarea_create(parent, NULL);
  
 
 lv_obj_t * text_label;
  text_label =(dummy_text_label *)malloc(size_dummy_label * sizeof(dummy_text_label));
 for(int i=0; i<=size_dummy_label ; i++)
   {
    text_label[i]=lv_textarea_create(parent, NULL);
    lv_obj_set_size(dummy_text_label[i], 20, 10);
    lv_obj_align(dummy_text_label[i], NULL, LV_ALIGN_CENTER, -145+, -70+(i*10));
   }
}
2

As far as I understand every create-method uses lv_mem_alloc for newly created object, so you couldn’t use additional alloc for it. To free allocated memory you need to use lv_obj_del

1 Like
3

Hallo glory-man,
thanks for your answer.

I’ve now found a way to creat an array with objects i need dynamicly.

typedef struct
{
   lv_obj_t * dummy_text_label;
}my_struct;

my_struct * MyStruct = (my_struct *)malloc(sizeof(my_struct)*5);

MyStruct[3].dummy_text_label = lv_textarea_create(parent, NULL);
lv_textarea_add_text(MyStruct[3].dummy_text_label, "Hallo");```

It works well.
4

I think such code also should work

lv_obj_t * dummy_text_label[5];

dummy_text_label[3] = lv_textarea_create(parent, NULL);
lv_textarea_add_text(dummy_text_label[3], "Hallo");
5

Yes it should too, but not dynamicly while the program is running. And that’s the point.

7

if you call this function 5 times

void dyn_create(lv_obj_t * parent)
{
  lv_obj_t * dummy_text_label[5];

  for(int i = 0; i < 5; i++)
  {
    dummy_text_label[i] = lv_textarea_create(parent, NULL);
    lv_textarea_add_text(dummy_text_label[i], "Hallo");
  }
}

your program will creates 25 textarea objects.
Also you can use such programm with a similar result

void dyn_create(lv_obj_t * parent)
{
  for(int i = 0; i < 5; i++)
  {
    lv_obj_t * dummy_text_label = lv_textarea_create(parent, NULL);
    lv_textarea_add_text(dummy_text_label, "Hallo");
    lv_obj_align(dummy_text_label, NULL, LV_ALIGN_CENTER, -145+i, -70+(i*10));
  }
}