feat(event) add LV_EVENT_SCREEN_LOADED/UNLOADED events

docs/overview/event.md

@@ -110,6 +110,8 @@ The following event codes exist:
 - `LV_EVENT_STYLE_CHANGED`    Object's style has changed
 - `LV_EVENT_BASE_DIR_CHANGED` The base dir has changed
 - `LV_EVENT_GET_SELF_SIZE`    Get the internal size of a widget
+- `LV_EVENT_SCREEN_LOADED`    A screen was loaded
+- `LV_EVENT_SCREEN_UNLOADED`  A screen was unloaded
 
 ### Special events
 - `LV_EVENT_VALUE_CHANGED`    The object's value has changed (i.e. slider moved)

src/core/lv_disp.c

@@ -82,8 +82,13 @@ void lv_disp_load_scr(lv_obj_t * scr)
 {
     lv_disp_t * d = lv_obj_get_disp(scr);
     if(!d) return;  /*Shouldn't happen, just to be sure*/
+
+    if(d->act_scr) lv_event_send(d->act_scr, LV_EVENT_SCREEN_UNLOADED, NULL);
+
     d->act_scr = scr;
 
+    if(d->act_scr) lv_event_send(d->act_scr, LV_EVENT_SCREEN_LOADED, NULL);
+
     lv_obj_invalidate(scr);
 }
 

src/core/lv_event.h

@@ -75,6 +75,9 @@ typedef enum {
     LV_EVENT_CHILD_CHANGED,       /**< Child was removed, added, or its size, position were changed */
     LV_EVENT_CHILD_CREATED,       /**< Child was created, always bubbles up to all parents*/
     LV_EVENT_CHILD_DELETED,       /**< Child was deleted, always bubbles up to all parents*/
+    LV_EVENT_SCREEN_LOADED,       /**< A screen was loaded*/
+    LV_EVENT_SCREEN_UNLOADED,     /**< A screen was unloaded*/
+
     LV_EVENT_SIZE_CHANGED,        /**< Object coordinates/size have changed*/
     LV_EVENT_STYLE_CHANGED,       /**< Object's style has changed*/
     LV_EVENT_LAYOUT_CHANGED,      /**< The children position has changed due to a layout recalculation*/