feat(bar): add data binding to the bar

Co-authored-by: cubic-dev-ai[bot] <191113872+cubic-dev-ai[bot]@users.noreply.github.com>

docs/src/details/widgets/bar.rst

@@ -73,6 +73,20 @@ The Bar can be one of the following modes:
   :cpp:expr:`lv_bar_set_start_value(bar, new_value, LV_ANIM_ON/OFF)`. The start
   value must be smaller than the end value.
 
+Data binding
+------------
+
+To get familiar with observers, subjects, and data bindings in general visit the
+:ref:`Observer <observer_how_to_use>` page.
+
+This method of subscribing to an integer Subject affects a Bar Widget's integer
+value directly.  Note that this is a one-way binding (Subject ==> Widget) so when
+the subject changes the Bar will be updated too.
+
+It supports integer and float subjects.
+
+- :cpp:expr:`lv_bar_bind_value(bar, &subject)`
+
 
 
 .. _lv_bar_events:

src/widgets/bar/lv_bar.c

@@ -14,6 +14,7 @@
 #if LV_USE_BAR != 0
 
 #include "../../draw/lv_draw.h"
+#include "../../others/observer/lv_observer_private.h"
 #include "../../misc/lv_assert.h"
 #include "../../misc/lv_anim_private.h"
 #include "../../misc/lv_math.h"
@@ -58,6 +59,10 @@ static void lv_bar_init_anim(lv_obj_t * bar, lv_bar_anim_t * bar_anim);
 static void lv_bar_anim(void * bar, int32_t value);
 static void lv_bar_anim_completed(lv_anim_t * a);
 
+#if LV_USE_OBSERVER
+    static void bar_value_observer_cb(lv_observer_t * observer, lv_subject_t * subject);
+#endif
+
 /**********************
  *  STATIC VARIABLES
  **********************/
@@ -249,6 +254,22 @@ bool lv_bar_is_symmetrical(lv_obj_t * obj)
             bar->start_value == bar->min_value;
 }
 
+#if LV_USE_OBSERVER
+lv_observer_t * lv_bar_bind_value(lv_obj_t * obj, lv_subject_t * subject)
+{
+    LV_ASSERT_NULL(subject);
+    LV_ASSERT_NULL(obj);
+
+    if(subject->type != LV_SUBJECT_TYPE_INT && subject->type != LV_SUBJECT_TYPE_FLOAT) {
+        LV_LOG_WARN("Incompatible subject type: %d", subject->type);
+        return NULL;
+    }
+
+    lv_observer_t * observer = lv_subject_add_observer_obj(subject, bar_value_observer_cb, obj, NULL);
+    return observer;
+}
+#endif /*LV_USE_OBSERVER*/
+
 /**********************
  *   STATIC FUNCTIONS
  **********************/
@@ -712,4 +733,20 @@ static void lv_bar_init_anim(lv_obj_t * obj, lv_bar_anim_t * bar_anim)
     bar_anim->anim_state = LV_BAR_ANIM_STATE_INV;
 }
 
+#if LV_USE_OBSERVER
+
+static void bar_value_observer_cb(lv_observer_t * observer, lv_subject_t * subject)
+{
+    if(subject->type == LV_SUBJECT_TYPE_INT) {
+        lv_bar_set_value(observer->target, subject->value.num, LV_ANIM_OFF);
+    }
+#if LV_USE_FLOAT
+    else {
+        lv_bar_set_value(observer->target, (int32_t)subject->value.float_v, LV_ANIM_OFF);
+    }
+#endif
+}
+
+#endif /*LV_USE_OBSERVER*/
+
 #endif

src/widgets/bar/lv_bar.h

@@ -164,6 +164,16 @@ lv_bar_orientation_t lv_bar_get_orientation(lv_obj_t * obj);
 */
 bool lv_bar_is_symmetrical(lv_obj_t * obj);
 
+#if LV_USE_OBSERVER
+/**
+ * Bind an integer or float Subject to a Bar's value.
+ * @param obj       pointer to Bar
+ * @param subject   pointer to Subject
+ * @return          pointer to newly-created Observer
+ */
+lv_observer_t * lv_bar_bind_value(lv_obj_t * obj, lv_subject_t * subject);
+#endif
+
 /**********************
  *      MACROS
  **********************/

xmls/lv_bar.xml

@@ -33,5 +33,7 @@ Example
 	    <prop name="mode" type="enum:lv_bar_mode"/>
 
 	    <prop name="orientation" type="enum:lv_bar_orientation"/>
+
+        <prop name="bind_value" type="subject" />
 	</api>
 </widget>