How to stop scrolling beyond endpoints in roller

How-to
1

image
i want to stop scrolling beyond endpoint for example scrolling down removed january from selection area it should lock

2

Hi @isfandcielo,

To prevent scrolling beyond the content endpoints you have two main approaches:

  • lv_obj_scroll_by_bounded()
lv_obj_scroll_by_bounded(my_obj, 0, -20, LV_ANIM_ON);
  • Use Snap Points to Lock Items in Place

lv_obj_set_scroll_snap_y(container, LV_SCROLL_SNAP_CENTER);

lv_obj_add_flag(container, LV_OBJ_FLAG_SCROLL_ONE);

lv_obj_add_flag(child_item, LV_OBJ_FLAG_SNAPPABLE);
3

i have tried these three option they don’t work my roller still get dragged when scrolled beyond end point but it does come back and to last value
I was looking for to not even scroll beyond end points

Blockquote
LV_DRAW_BUF_DEFINE_STATIC(mask, 130, 150, LV_COLOR_FORMAT_L8);
LV_DRAW_BUF_INIT_STATIC(mask);
lv_obj_t *roller
= lv_obj_find_by_name(lv_screen_active(), “temp_setpnt_roller”);
if(roller == NULL)
return;

// lv_obj_scroll_by_bounded(roller, 0, 0, LV_ANIM_OFF);

lv_obj_set_scroll_snap_y(roller, LV_SCROLL_SNAP_CENTER);

lv_obj_add_flag(roller, LV_OBJ_FLAG_SCROLL_ONE);

lv_obj_add_flag(roller, LV_OBJ_FLAG_SNAPPABLE);

also lvgl ui pro editor doesnot have these option so had to branch the code to make this happen

4

@halyssonJr

5

roller_test.zip (289.7 KB)

Hi @isfandcielo ,

Now I understand what happened: the roller isn’t used to scroll, but it’s intercepted by LV_EVENT_PRESSING. So, you need to add a handler for LV_EVENT_PRESSING and re-clamp the y-axis before any draw event.

static void roller_clamp_top_cb(lv_event_t * e)
{
    lv_obj_t * roller = lv_event_get_current_target_obj(e);
    lv_obj_t * label = lv_obj_get_child(roller, 0);
    if(label == NULL) return;

    const lv_font_t * font = lv_obj_get_style_text_font(roller, LV_PART_MAIN);
    int32_t line_space = lv_obj_get_style_text_line_space(roller, LV_PART_MAIN);
    int32_t font_h = lv_font_get_line_height(font);
    int32_t content_h = lv_obj_get_content_height(roller);
    int32_t mid_y1 = content_h / 2 - font_h / 2;   /*label y for index 0*/

    if(lv_obj_get_y_aligned(label) > mid_y1) {
        lv_obj_set_y(label, mid_y1);
    }
} 

...
lv_obj_add_event_cb(roller1, roller_clamp_top_cb, LV_EVENT_PRESSING, NULL);