feat(events): add event trickle mechanism to propagate events to children (#8415)

Co-authored-by: Gauthier Provost <gpr@interel.com>

examples/event/index.rst

@@ -22,6 +22,11 @@ Event bubbling
 .. lv_example:: event/lv_example_event_bubble
   :language: c
 
+Event trickle-down
+------------------
+.. lv_example:: event/lv_example_event_trickle
+  :language: c
+
 Draw event
 ----------
 .. lv_example:: event/lv_example_event_draw

examples/event/lv_example_event.h

@@ -29,6 +29,7 @@ void lv_example_event_click(void);
 void lv_example_event_streak(void);
 void lv_example_event_button(void);
 void lv_example_event_bubble(void);
+void lv_example_event_trickle(void);
 void lv_example_event_draw(void);
 
 /**********************

examples/event/lv_example_event_trickle.c

@@ -0,0 +1,37 @@
+#include "../lv_examples.h"
+#if LV_BUILD_EXAMPLES && LV_USE_FLEX
+
+/**
+ * Demonstrate event trickle
+ */
+void lv_example_event_trickle(void)
+{
+    lv_obj_t * cont = lv_obj_create(lv_screen_active());
+    lv_obj_set_size(cont, 290, 200);
+    lv_obj_center(cont);
+    lv_obj_set_flex_flow(cont, LV_FLEX_FLOW_ROW_WRAP);
+
+    static lv_style_t style_black;
+    lv_style_init(&style_black);
+    lv_style_set_text_color(&style_black, lv_color_white());
+    lv_style_set_bg_color(&style_black, lv_color_black());
+
+    /*Enable event trickle-down on the container*/
+    lv_obj_add_flag(cont, LV_OBJ_FLAG_EVENT_TRICKLE);
+
+    lv_obj_add_style(cont, &style_black, LV_STATE_PRESSED);
+
+    uint32_t i;
+    for(i = 0; i < 9; i++) {
+        lv_obj_t * subcont = lv_obj_create(cont);
+        lv_obj_set_size(subcont, 70, 50);
+
+        lv_obj_t * label = lv_label_create(subcont);
+        lv_label_set_text_fmt(label, "%" LV_PRIu32, i);
+
+        /*Add style to the label when clicked*/
+        lv_obj_add_style(subcont, &style_black, LV_STATE_FOCUSED);
+    }
+}
+
+#endif