This code places seven Elementary slider widgets on a window, each of them exemplifying a part of the widget's API.

The first of them is the default slider:

   sl = elm_slider_add(win);
   evas_object_size_hint_align_set(sl, EVAS_HINT_FILL, 0.5);
   evas_object_size_hint_weight_set(sl, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_box_pack_end(bx, sl);
   evas_object_show(sl);

As you see, the defaults for a slider are:

horizontal
no label
no values (on indicator or unit labels)

Actually it's pretty useless this way. So let's learn how to improve it.

If some decoration is required, a label can be set, and icon before and after the bar as well. On the second slider will add a home icon and a folder icon at end.

   elm_object_text_set(sl, "Counter");

   ic = elm_icon_add(win);
   elm_icon_standard_set(ic, "home");
   elm_image_resizable_set(ic, EINA_FALSE, EINA_FALSE);
   elm_object_part_content_set(sl, "icon", ic);

   ic = elm_icon_add(win);
   elm_icon_standard_set(ic, "folder");
   elm_image_resizable_set(ic, EINA_FALSE, EINA_FALSE);
   elm_object_part_content_set(sl, "end", ic);

If the bar size need to be changed, it can be done with span set function, that doesn't accounts other widget's parts size. Also the bar can starts with a not default value (0.0), as we done on third slider:

   elm_slider_value_set(sl, 1);
   elm_slider_span_size_set(sl, 200);

So far, users won't be able to see the slider value. If it's required, it can be displayed in two different areas, units label or above the indicator.

Let's place a units label on our widget, and also let's set minimum and maximum value (uses 0.0 and 1.0 by default):

   elm_slider_unit_format_set(sl, "%1.0f units");
   elm_slider_min_max_set(sl, 0, 100);

If above the indicator is the place to display the value, just set it. Also, is possible to invert a bar, as you can see:

   elm_slider_indicator_format_set(sl, "%1.2f");
   elm_slider_inverted_set(sl, EINA_TRUE);

But if you require to use a function a bit more customized to show the value, is possible to registry a callback function that will be called to display unit or indicator label. Only the value will be passed to this function, that should return a string. In this case, a function to free this string will be required.

Let's exemplify with indicator label on our sixth slider:

static void
_indicator_free(char *str)
{
   free(str);
}

EAPI_MAIN int
elm_main(int argc EINA_UNUSED, char **argv EINA_UNUSED)
{
   Evas_Object *win, *bx, *sl, *ic;

   elm_policy_set(ELM_POLICY_QUIT, ELM_POLICY_QUIT_LAST_WINDOW_CLOSED);

   win = elm_win_util_standard_add("slider", "Slider Example");
   elm_win_autodel_set(win, EINA_TRUE);

   bx = elm_box_add(win);
   evas_object_size_hint_weight_set(bx, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_win_resize_object_add(win, bx);
   evas_object_show(bx);

   /* default */
   sl = elm_slider_add(win);
   evas_object_size_hint_align_set(sl, EVAS_HINT_FILL, 0.5);
   evas_object_size_hint_weight_set(sl, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_box_pack_end(bx, sl);
   evas_object_show(sl);

   /* with icon, end and label */
   sl = elm_slider_add(win);
   elm_object_text_set(sl, "Counter");

   ic = elm_icon_add(win);
   elm_icon_standard_set(ic, "home");
   elm_image_resizable_set(ic, EINA_FALSE, EINA_FALSE);
   elm_object_part_content_set(sl, "icon", ic);

   ic = elm_icon_add(win);
   elm_icon_standard_set(ic, "folder");
   elm_image_resizable_set(ic, EINA_FALSE, EINA_FALSE);
   elm_object_part_content_set(sl, "end", ic);

   evas_object_size_hint_align_set(sl, EVAS_HINT_FILL, 0.5);
   evas_object_size_hint_weight_set(sl, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_box_pack_end(bx, sl);
   evas_object_show(sl);

   /* value set and span size */
   sl = elm_slider_add(win);
   elm_slider_value_set(sl, 1);
   elm_slider_span_size_set(sl, 200);
   evas_object_size_hint_align_set(sl, EVAS_HINT_FILL, 0.5);
   evas_object_size_hint_weight_set(sl, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_box_pack_end(bx, sl);
   evas_object_show(sl);

   /* with unit label and min - max */
   sl = elm_slider_add(win);
   elm_slider_unit_format_set(sl, "%1.0f units");
   elm_slider_min_max_set(sl, 0, 100);
   evas_object_size_hint_align_set(sl, EVAS_HINT_FILL, 0.5);
   evas_object_size_hint_weight_set(sl, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_box_pack_end(bx, sl);
   evas_object_show(sl);

   /* with indicator label and inverted */
   sl = elm_slider_add(win);
   elm_slider_indicator_format_set(sl, "%1.2f");
   elm_slider_inverted_set(sl, EINA_TRUE);
   evas_object_size_hint_align_set(sl, EVAS_HINT_FILL, 0.5);
   evas_object_size_hint_weight_set(sl, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_box_pack_end(bx, sl);
   evas_object_show(sl);

   /* vertical with indicator format func */
   sl = elm_slider_add(win);
   elm_slider_horizontal_set(sl, EINA_FALSE);
   elm_slider_indicator_format_function_set(sl, _indicator_format,
                                            _indicator_free);
   evas_object_size_hint_align_set(sl, 0.5, EVAS_HINT_FILL);
   evas_object_size_hint_weight_set(sl, 0, EVAS_HINT_EXPAND);
   elm_box_pack_end(bx, sl);
   evas_object_show(sl);

   /* callbacks */
   sl = elm_slider_add(win);
   elm_slider_unit_format_set(sl, "%1.3f units");
   evas_object_size_hint_align_set(sl, EVAS_HINT_FILL, 0.5);
   evas_object_size_hint_weight_set(sl, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   elm_box_pack_end(bx, sl);
   evas_object_show(sl);
   evas_object_smart_callback_add(sl, "changed", _changed_cb, NULL);
   evas_object_smart_callback_add(sl, "delay,changed", _delay_changed_cb, NULL);

   evas_object_show(win);

   elm_run();

   return 0;
}

Setting callback functions:

Also, a slider can be displayed vertically:

   elm_slider_horizontal_set(sl, EINA_FALSE);

Finally the last widget will exemplify how to listen for widget's signals, changed and delay,changed . First we need to implement callback functions that will simply print slider's value:

static void
_delay_changed_cb(void *data EINA_UNUSED, Evas_Object *obj, void *event_info EINA_UNUSED)
{
   double val = elm_slider_value_get(obj);
   printf("Delay changed to %1.2f\n", val);
}

static char*
_indicator_format(double val)
{
   char *indicator = malloc(sizeof(char) * 32);
   snprintf(indicator, 32, "%1.2f u", val);
   return indicator;
}

The first callback function should be called everytime value changes, the second one only after user stops to increment or decrement. Try to keep arrows pressed and check the difference.

   evas_object_smart_callback_add(sl, "changed", _changed_cb, NULL);
   evas_object_smart_callback_add(sl, "delay,changed", _delay_changed_cb, NULL);

See the full source code for this example.