In this example, we illustrate how to create and handle Evas smart interfaces. Note that we use the same code base of the Evas object smart objects example, here. We just augment it with an interfaces demonstration.

A smart interface is just a functions interface a given smart object is declaring to support and or use. In Evas, interfaces are very simple: no interface inheritance, no interface overriding. Their purpose is to extend an object's capabilities and behavior beyond the sub-classing schema.

Here, together with a custom smart object, we create and declare the object as using an Evas interface. It'll have a custom function, too, besides the add() and del() obligatory ones. To demonstrate interface data, which is bound to object instances, we'll have a string as this data.

Here is where we declare our interface:

static const char iface1_data[] = "iface1_data";
static const char IFACE1_NAME[] = "iface1";

static Eina_Bool _iface1_add(Evas_Object *);
static void      _iface1_del(Evas_Object *);
static void      _iface1_custom_fn(Evas_Object *);

typedef struct _Evas_Smart_Example_Interface Evas_Smart_Example_Interface;
struct _Evas_Smart_Example_Interface
{
   Evas_Smart_Interface base;
   void                 (*example_func)(Evas_Object *obj);
};

static Evas_Smart_Example_Interface iface1;

static Eina_Bool
_iface1_add(Evas_Object *obj EINA_UNUSED)
{
   printf("iface1's add()!\n");

   return EINA_TRUE;
}

static void
_iface1_del(Evas_Object *obj)
{
   printf("iface1's del()! Data is %s\n",
          (char *)evas_object_smart_interface_data_get
            (obj, (Evas_Smart_Interface *)&iface1));
}

static void
_iface1_custom_fn(Evas_Object *obj EINA_UNUSED)
{
   printf("iface1's custom_fn()!\n");
}

static const Evas_Smart_Interface *_smart_interfaces[] =
{
   (Evas_Smart_Interface *)&iface1, NULL
};

Note that there's error checking for interfaces creation, by means of the add() method's return value (_iface1_add(), here).

Now note that here we are filling in the interface's fields dynamically. Let's move on to that code region:

   iface = (Evas_Smart_Example_Interface *)&iface1;
   iface->base.name = IFACE1_NAME;
   iface->base.private_size = sizeof(iface1_data);
   iface->base.add = _iface1_add;
   iface->base.del = _iface1_del;
   iface->example_func = _iface1_custom_fn;

   d.smt = evas_smart_example_add(d.evas);

As important as setting the function pointers, is declaring the private_size as to match exactly the size of the data blob we want to have allocated for us by Evas. This will happen automatically inside evas_smart_example_add(). Later, on this code, we deal exactly with that data blob, more specifically writing on it (as it's not done inside _iface1_add(), here:

   iface = (Evas_Smart_Example_Interface *)evas_object_smart_interface_get
       (d.smt, IFACE1_NAME);
   if (iface)
     {
        char *data;

        fprintf(stdout, "We've found a smart interface on the smart object!"
                        "\n\tname: %s\n", iface->base.name);

        fprintf(stdout, "Setting its interface data...\n");
        data = evas_object_smart_interface_data_get
            (d.smt, (Evas_Smart_Interface *)iface);
        memcpy(data, iface1_data, sizeof(iface1_data));

        fprintf(stdout, "Calling an interface's function...\n");
        iface->example_func(d.smt);
     }

Before accessing the interface data, we exercise the interface fetching call evas_object_smart_interface_get(), with the name string we used to be interface's name. With that handle in hands, we issue evas_object_smart_interface_data_get() and write the string we want as data on that memory region. That will make up for the string you get on _iface1_del().

The full example follows.

#ifdef HAVE_CONFIG_H
#include "config.h"
#else
#define PACKAGE_EXAMPLES_DIR "."
#endif

#include <Ecore.h>
#include <Ecore_Evas.h>
#include <stdio.h>
#include <errno.h>

#define WIDTH  (320)
#define HEIGHT (240)

static const char *commands = \
  "commands are:\n"
  "\tl - insert child rectangle on the left\n"
  "\tr - insert child rectangle on the right\n"
  "\tw - remove and delete all members from the smart object\n"
  "\tright arrow - move smart object to the right\n"
  "\tleft arrow - move smart object to the left\n"
  "\tup arrow - move smart object up\n"
  "\tdown arrow - move smart object down\n"
  "\td - decrease smart object's size\n"
  "\ti - increase smart object's size\n"
  "\tc - change smart object's clipper color\n"
  "\th - print help\n"
  "\tq - quit\n"
;

#define WHITE {255, 255, 255, 255}
#define RED   {255, 0, 0, 255}
#define GREEN {0, 255, 0, 255}
#define BLUE  {0, 0, 255, 255}

struct test_data
{
   Ecore_Evas  *ee;
   Evas        *evas;
   Evas_Object *smt, *bg, *clipper, *rects[2];
};

struct color_tuple
{
   int r, g, b, a;
} clipper_colors[4] = {WHITE, RED, GREEN, BLUE};
int cur_color = 0;

static const char *
_index_to_color(int i)
{
   switch (i)
     {
      case 0:
        return "WHITE (default)";

      case 1:
        return "RED";

      case 2:
        return "GREEN";

      case 3:
        return "BLUE";

      default:
        return "other";
     }
}

static struct test_data d = {0};
static const char *border_img_path = PACKAGE_EXAMPLES_DIR "/red.png";

#define _evas_smart_example_type "Evas_Smart_Example"

static const char iface1_data[] = "iface1_data";
static const char IFACE1_NAME[] = "iface1";

static Eina_Bool _iface1_add(Evas_Object *);
static void      _iface1_del(Evas_Object *);
static void      _iface1_custom_fn(Evas_Object *);

typedef struct _Evas_Smart_Example_Interface Evas_Smart_Example_Interface;
struct _Evas_Smart_Example_Interface
{
   Evas_Smart_Interface base;
   void                 (*example_func)(Evas_Object *obj);
};

static Evas_Smart_Example_Interface iface1;

static Eina_Bool
_iface1_add(Evas_Object *obj EINA_UNUSED)
{
   printf("iface1's add()!\n");

   return EINA_TRUE;
}

static void
_iface1_del(Evas_Object *obj)
{
   printf("iface1's del()! Data is %s\n",
          (char *)evas_object_smart_interface_data_get
            (obj, (Evas_Smart_Interface *)&iface1));
}

static void
_iface1_custom_fn(Evas_Object *obj EINA_UNUSED)
{
   printf("iface1's custom_fn()!\n");
}

static const Evas_Smart_Interface *_smart_interfaces[] =
{
   (Evas_Smart_Interface *)&iface1, NULL
};

#define EVT_CHILDREN_NUMBER_CHANGED "children,changed"

static const Evas_Smart_Cb_Description _smart_callbacks[] =
{
   {EVT_CHILDREN_NUMBER_CHANGED, "i"},
   {NULL, NULL}
};

typedef struct _Evas_Smart_Example_Data Evas_Smart_Example_Data;
/*
 * This structure augments clipped smart object's instance data,
 * providing extra members required by our example smart object's
 * implementation.
 */
struct _Evas_Smart_Example_Data
{
   Evas_Object_Smart_Clipped_Data base;
   Evas_Object                   *children[2], *border;
   int                            child_count;
};

#define EVAS_SMART_EXAMPLE_DATA_GET(o, ptr) \
  Evas_Smart_Example_Data * ptr = evas_object_smart_data_get(o)

#define EVAS_SMART_EXAMPLE_DATA_GET_OR_RETURN(o, ptr)        \
  EVAS_SMART_EXAMPLE_DATA_GET(o, ptr);                       \
  if (!ptr)                                                  \
    {                                                        \
       fprintf(stderr, "No widget data for object %p (%s)!", \
               o, evas_object_type_get(o));                  \
       fflush(stderr);                                       \
       abort();                                              \
       return;                                               \
    }

#define EVAS_SMART_EXAMPLE_DATA_GET_OR_RETURN_VAL(o, ptr, val) \
  EVAS_SMART_EXAMPLE_DATA_GET(o, ptr);                         \
  if (!ptr)                                                    \
    {                                                          \
       fprintf(stderr, "No widget data for object %p (%s)!",   \
               o, evas_object_type_get(o));                    \
       fflush(stderr);                                         \
       abort();                                                \
       return val;                                             \
    }

EVAS_SMART_SUBCLASS_IFACE_NEW
  (_evas_smart_example_type, _evas_smart_example, Evas_Smart_Class,
  Evas_Smart_Class, evas_object_smart_clipped_class_get, _smart_callbacks,
  _smart_interfaces);

static void
_on_destroy(Ecore_Evas *ee EINA_UNUSED)
{
   ecore_main_loop_quit();
}

/* here just to keep our example's window size and background image's
 * size in synchrony */
static void
_canvas_resize_cb(Ecore_Evas *ee)
{
   int w, h;

   ecore_evas_geometry_get(ee, NULL, NULL, &w, &h);
   evas_object_resize(d.bg, w, h);
}

static void
_on_child_del(void *data,
              Evas *evas EINA_UNUSED,
              Evas_Object *o,
              void *einfo EINA_UNUSED)
{
   Evas_Object *example_smart = data;
   long idx;

   EVAS_SMART_EXAMPLE_DATA_GET(example_smart, priv);

   idx = (long)(uintptr_t)evas_object_data_get(o, "index");
   idx--;

   priv->children[idx] = NULL;

   evas_object_smart_member_del(o);
   evas_object_smart_changed(example_smart);
}

static void
_evas_smart_example_child_callbacks_unregister(Evas_Object *obj)
{
   evas_object_data_set(obj, "index", NULL);
   evas_object_event_callback_del(obj, EVAS_CALLBACK_FREE, _on_child_del);
}

static void
_evas_smart_example_child_callbacks_register(Evas_Object *o,
                                             Evas_Object *child,
                                             long idx)
{
   evas_object_event_callback_add(child, EVAS_CALLBACK_FREE, _on_child_del, o);
   evas_object_data_set(child, "index", (void *)(uintptr_t)(++idx));
}

/* create and setup a new example smart object's internals */
static void
_evas_smart_example_smart_add(Evas_Object *o)
{
   EVAS_SMART_DATA_ALLOC(o, Evas_Smart_Example_Data);

   /* this is a border around the smart object's area, delimiting it */
   priv->border = evas_object_image_filled_add(evas_object_evas_get(o));
   evas_object_image_file_set(priv->border, border_img_path, NULL);
   evas_object_image_border_set(priv->border, 3, 3, 3, 3);
   evas_object_image_border_center_fill_set(
     priv->border, EVAS_BORDER_FILL_NONE);
   evas_object_smart_member_add(priv->border, o);

   _evas_smart_example_parent_sc->add(o);
}

static void
_evas_smart_example_smart_del(Evas_Object *o)
{
   EVAS_SMART_EXAMPLE_DATA_GET(o, priv);

   if (priv->children[0])
     {
        _evas_smart_example_child_callbacks_unregister(priv->children[0]);
        priv->children[0] = NULL;
     }

   if (priv->children[1])
     {
        _evas_smart_example_child_callbacks_unregister(priv->children[1]);
        priv->children[1] = NULL;
     }

   _evas_smart_example_parent_sc->del(o);
}

static void
_evas_smart_example_smart_show(Evas_Object *o)
{
   EVAS_SMART_EXAMPLE_DATA_GET(o, priv);

   if (priv->children[0]) evas_object_show(priv->children[0]);
   if (priv->children[1]) evas_object_show(priv->children[1]);
   evas_object_show(priv->border);

   _evas_smart_example_parent_sc->show(o);
}

static void
_evas_smart_example_smart_hide(Evas_Object *o)
{
   EVAS_SMART_EXAMPLE_DATA_GET(o, priv);

   if (priv->children[0]) evas_object_hide(priv->children[0]);
   if (priv->children[1]) evas_object_hide(priv->children[1]);
   evas_object_hide(priv->border);

   _evas_smart_example_parent_sc->hide(o);
}

static void
_evas_smart_example_smart_resize(Evas_Object *o,
                                 Evas_Coord w,
                                 Evas_Coord h)
{
   Evas_Coord ow, oh;
   evas_object_geometry_get(o, NULL, NULL, &ow, &oh);
   if ((ow == w) && (oh == h)) return;

   /* this will trigger recalculation */
   evas_object_smart_changed(o);
}

/* act on child objects' properties, before rendering */
static void
_evas_smart_example_smart_calculate(Evas_Object *o)
{
   Evas_Coord x, y, w, h;

   EVAS_SMART_EXAMPLE_DATA_GET_OR_RETURN(o, priv);
   evas_object_geometry_get(o, &x, &y, &w, &h);

   evas_object_resize(priv->border, w, h);
   evas_object_move(priv->border, x, y);

   if (priv->children[0])
     {
        evas_object_move(priv->children[0], x + 3, y + 3);
        evas_object_resize(priv->children[0], (w / 2) - 3, (h / 2) - 3);
     }

   if (priv->children[1])
     {
        evas_object_move(priv->children[1], x + (w / 2), y + (h / 2));
        evas_object_resize(priv->children[1], (w / 2) - 3, (h / 2) - 3);
     }
}

/* setting our smart interface */
static void
_evas_smart_example_smart_set_user(Evas_Smart_Class *sc)
{
   /* specializing these two */
   sc->add = _evas_smart_example_smart_add;
   sc->del = _evas_smart_example_smart_del;
   sc->show = _evas_smart_example_smart_show;
   sc->hide = _evas_smart_example_smart_hide;

   /* clipped smart object has no hook on resizes or calculations */
   sc->resize = _evas_smart_example_smart_resize;
   sc->calculate = _evas_smart_example_smart_calculate;
}

/* BEGINS example smart object's own interface */

/* add a new example smart object to a canvas */
Evas_Object *
evas_smart_example_add(Evas *evas)
{
   return evas_object_smart_add(evas, _evas_smart_example_smart_class_new());
}

static void
_evas_smart_example_remove_do(Evas_Smart_Example_Data *priv,
                              Evas_Object *child,
                              int idx)
{
   priv->children[idx] = NULL;
   priv->child_count--;
   _evas_smart_example_child_callbacks_unregister(child);
   evas_object_smart_member_del(child);
}

/* remove a child element, return its pointer (or NULL on errors) */
Evas_Object *
evas_smart_example_remove(Evas_Object *o,
                          Evas_Object *child)
{
   long idx;

   EVAS_SMART_EXAMPLE_DATA_GET_OR_RETURN_VAL(o, priv, NULL);

   if (priv->children[0] != child && priv->children[1] != child)
     {
        fprintf(stderr, "You are trying to remove something not belonging to"
                        " the example smart object!\n");
        return NULL;
     }

   idx = (long)(uintptr_t)evas_object_data_get(child, "index");
   idx--;

   _evas_smart_example_remove_do(priv, child, idx);

   evas_object_smart_callback_call(
     o, EVT_CHILDREN_NUMBER_CHANGED, (void *)(uintptr_t)priv->child_count);
   evas_object_smart_changed(o);

   return child;
}

/* set to return any previous object set to the left position of the
 * smart object or NULL, if any (or on errors) */
Evas_Object *
evas_smart_example_set_left(Evas_Object *o,
                            Evas_Object *child)
{
   Evas_Object *ret = NULL;

   EVAS_SMART_EXAMPLE_DATA_GET_OR_RETURN_VAL(o, priv, NULL);
   if (!child)
     return NULL;

   if (priv->children[1] == child)
     {
        fprintf(stderr, "You mustn't place a child on both slots of"
                        " the example smart object!\n");
        return NULL;
     }

   if (priv->children[0])
     {
        if (priv->children[0] != child)
          {
             ret = priv->children[0];
             _evas_smart_example_remove_do(priv, priv->children[0], 0);
          }
        else return child;
     }

   priv->children[0] = child;
   _evas_smart_example_child_callbacks_register(o, child, 0);
   evas_object_smart_member_add(child, o);
   evas_object_smart_changed(o);

   priv->child_count++;
   if (!ret)
     {
        evas_object_smart_callback_call(
          o, EVT_CHILDREN_NUMBER_CHANGED, (void *)(uintptr_t)priv->child_count);
     }

   return ret;
}

/* set to return any previous object set to the right position of the
 * smart object or NULL, if any (or on errors) */
Evas_Object *
evas_smart_example_set_right(Evas_Object *o,
                             Evas_Object *child)
{
   Evas_Object *ret = NULL;

   EVAS_SMART_EXAMPLE_DATA_GET_OR_RETURN_VAL(o, priv, NULL);
   if (!child)
     return NULL;

   if (priv->children[0] == child)
     {
        fprintf(stderr, "You mustn't place a child on both slots of"
                        " the example smart object!\n");
        return NULL;
     }

   if (priv->children[1])
     {
        if (priv->children[1] != child)
          {
             ret = priv->children[1];
             _evas_smart_example_remove_do(priv, priv->children[1], 1);
          }
        else return child;
     }

   priv->children[1] = child;
   _evas_smart_example_child_callbacks_register(o, child, 1);
   evas_object_smart_member_add(child, o);
   evas_object_smart_changed(o);

   priv->child_count++;
   if (!ret)
     {
        evas_object_smart_callback_call(
          o, EVT_CHILDREN_NUMBER_CHANGED, (void *)(uintptr_t)priv->child_count);
     }

   return ret;
}

/* END OF example smart object's own interface */

static void
_on_keydown(void *data EINA_UNUSED,
            Evas *evas EINA_UNUSED,
            Evas_Object *o EINA_UNUSED,
            void *einfo)
{
   Evas_Event_Key_Down *ev = einfo;

   if (strcmp(ev->key, "q") == 0) /* print help */
     {
        _on_destroy(NULL);
        return;
     }

   if (strcmp(ev->key, "h") == 0) /* print help */
     {
        fprintf(stdout, commands);
        return;
     }

   if (strcmp(ev->key, "w") == 0) /* clear out smart object (WRT
                                       * members) */
     {
        if (d.rects[0])
          {
             evas_smart_example_remove(d.smt, d.rects[0]);
             evas_object_del(d.rects[0]);
          }
        if (d.rects[1])
          {
             evas_smart_example_remove(d.smt, d.rects[1]);
             evas_object_del(d.rects[1]);
          }

        memset(d.rects, 0, sizeof(d.rects));

        fprintf(stdout, "Deleting all members of the smart object.\n");

        return;
     }

   if (strcmp(ev->key, "l") == 0) /* insert random colored
                                       * rectangle on the left */
     {
        Evas_Object *rect = evas_object_rectangle_add(d.evas), *prev;
        evas_object_color_set(
          rect, rand() % 255, rand() % 255, rand() % 255, 255);
        evas_object_show(rect);

        prev = evas_smart_example_set_left(d.smt, rect);
        d.rects[0] = rect;

        fprintf(stdout, "Setting smart object's left spot with a new"
                        " rectangle.\n");
        fprintf(stdout, "Checking its new smart object parent: %s\n",
                evas_object_smart_parent_get(rect) == d.smt ? "OK!" :
                "Failure!");
        if (prev)
          {
             int r, g, b;

             evas_object_color_get(prev, &r, &g, &b, NULL);
             fprintf(stdout, "Deleting previous left child,"
                             " which had colors (%d, %d, %d)\n", r, g, b);
             evas_object_del(prev);
          }

        return;
     }

   if (strcmp(ev->key, "r") == 0) /* insert random colored
                                       * rectangle on the right */
     {
        Evas_Object *rect = evas_object_rectangle_add(d.evas), *prev;
        evas_object_color_set(
          rect, rand() % 255, rand() % 255, rand() % 255, 255);
        evas_object_show(rect);

        prev = evas_smart_example_set_right(d.smt, rect);
        d.rects[1] = rect;

        fprintf(stdout, "Setting smart object's right spot with a new"
                        " rectangle.\n");
        fprintf(stdout, "Checking its new smart object parent: %s\n",
                evas_object_smart_parent_get(rect) == d.smt ? "OK!" :
                "Failure!");
        if (prev)
          {
             int r, g, b;

             evas_object_color_get(prev, &r, &g, &b, NULL);
             fprintf(stdout, "Deleting previous right child,"
                             " which had colors (%d, %d, %d)\n", r, g, b);
             evas_object_del(prev);
          }

        return;
     }

   /* move smart object along the canvas */
   if (strcmp(ev->key, "Right") == 0 || strcmp(ev->key, "Left") == 0 ||
       strcmp(ev->key, "Up") == 0 || strcmp(ev->key, "Down") == 0)
     {
        Evas_Coord x, y;

        evas_object_geometry_get(d.smt, &x, &y, NULL, NULL);

        switch (ev->key[0])
          {
           case 'R':
             x += 20;
             break;

           case 'L':
             x -= 20;
             break;

           case 'U':
             y -= 20;
             break;

           case 'D':
             y += 20;
             break;
          }

        evas_object_move(d.smt, x, y);

        return;
     }

   /* increase smart object's size */
   if (strcmp(ev->key, "i") == 0)
     {
        Evas_Coord w, h;

        evas_object_geometry_get(d.smt, NULL, NULL, &w, &h);

        w *= 1.1;
        h *= 1.1;

        evas_object_resize(d.smt, w, h);

        return;
     }

   /* decrease smart object's size */
   if (strcmp(ev->key, "d") == 0)
     {
        Evas_Coord w, h;

        evas_object_geometry_get(d.smt, NULL, NULL, &w, &h);

        w *= 0.9;
        h *= 0.9;

        evas_object_resize(d.smt, w, h);

        return;
     }

   /* change smart object's clipper color */
   if (strcmp(ev->key, "c") == 0)
     {
        cur_color = (cur_color + 1) % 4;

        evas_object_color_set(
          d.clipper, clipper_colors[cur_color].r, clipper_colors[cur_color].g,
          clipper_colors[cur_color].b, clipper_colors[cur_color].a);

        fprintf(stderr, "Changing clipper's color to %s\n",
                _index_to_color(cur_color));

        return;
     }
}

static void
/* callback on number of member objects changed */
_on_example_smart_object_child_num_change(void *data EINA_UNUSED,
                                          Evas_Object *obj EINA_UNUSED,
                                          void *event_info)
{
   fprintf(stdout, "Number of child members on our example smart"
                   " object changed to %llu\n", (unsigned long long)(uintptr_t)event_info);
}

int
main(void)
{
   const Evas_Smart_Cb_Description **descriptions;
   Evas_Smart_Example_Interface *iface;
   unsigned int count;
   Eina_Bool ret;

   srand(time(NULL));

   if (!ecore_evas_init())
     return EXIT_FAILURE;

   /* this will give you a window with an Evas canvas under the first
    * engine available */
   d.ee = ecore_evas_new(NULL, 10, 10, WIDTH, HEIGHT, NULL);
   if (!d.ee)
     goto error;

   ecore_evas_callback_destroy_set(d.ee, _on_destroy);
   ecore_evas_callback_resize_set(d.ee, _canvas_resize_cb);
   ecore_evas_show(d.ee);

   /* the canvas pointer, de facto */
   d.evas = ecore_evas_get(d.ee);

   d.bg = evas_object_rectangle_add(d.evas);
   evas_object_color_set(d.bg, 255, 255, 255, 255);
   evas_object_move(d.bg, 0, 0);
   evas_object_resize(d.bg, WIDTH, HEIGHT);
   evas_object_show(d.bg);

   iface = (Evas_Smart_Example_Interface *)&iface1;
   iface->base.name = IFACE1_NAME;
   iface->base.private_size = sizeof(iface1_data);
   iface->base.add = _iface1_add;
   iface->base.del = _iface1_del;
   iface->example_func = _iface1_custom_fn;

   d.smt = evas_smart_example_add(d.evas);

   evas_object_move(d.smt, WIDTH / 4, HEIGHT / 4);
   evas_object_resize(d.smt, WIDTH / 2, HEIGHT / 2);
   evas_object_show(d.smt);

   ret = evas_object_smart_type_check(d.smt, _evas_smart_example_type);
   fprintf(stdout, "Adding smart object of type \"%s\" to the canvas: %s.\n",
           _evas_smart_example_type, ret ? "success" : "failure");

   d.clipper = evas_object_smart_clipped_clipper_get(d.smt);
   fprintf(stdout, "Checking if clipped smart object's clipper is a "
                   "\"static\" one: %s\n", evas_object_static_clip_get(
             d.clipper) ? "yes" : "no");

   evas_object_color_set(
     d.clipper, clipper_colors[cur_color].r, clipper_colors[cur_color].g,
     clipper_colors[cur_color].b, clipper_colors[cur_color].a);

   evas_object_smart_callbacks_descriptions_get(
     d.smt, &descriptions, &count, NULL, NULL);

   for (; *descriptions; descriptions++)
     {
        fprintf(stdout, "We've found a smart callback on the smart object!"
                        "\n\tname: %s\n\ttype: %s\n", (*descriptions)->name,
                (*descriptions)->type);

        if (strcmp((*descriptions)->type, "i")) continue;
        /* we know we don't have other types of smart callbacks
         * here, just playing with it */

        /* for now, we know the only one callback is the one
         * reporting number of member objects changed on the
         * example smart object */
        evas_object_smart_callback_add(
          d.smt, (*descriptions)->name,
          _on_example_smart_object_child_num_change, NULL);
     }

   evas_object_focus_set(d.bg, EINA_TRUE);
   evas_object_event_callback_add(
     d.bg, EVAS_CALLBACK_KEY_DOWN, _on_keydown, NULL);

   iface = (Evas_Smart_Example_Interface *)evas_object_smart_interface_get
       (d.smt, IFACE1_NAME);
   if (iface)
     {
        char *data;

        fprintf(stdout, "We've found a smart interface on the smart object!"
                        "\n\tname: %s\n", iface->base.name);

        fprintf(stdout, "Setting its interface data...\n");
        data = evas_object_smart_interface_data_get
            (d.smt, (Evas_Smart_Interface *)iface);
        memcpy(data, iface1_data, sizeof(iface1_data));

        fprintf(stdout, "Calling an interface's function...\n");
        iface->example_func(d.smt);
     }

   fprintf(stdout, commands);
   ecore_main_loop_begin();

   ecore_evas_free(d.ee);
   ecore_evas_shutdown();
   return 0;

error:
   fprintf(stderr, "you got to have at least one evas engine built and linked"
                   " up to ecore-evas for this example to run properly.\n");
   ecore_evas_shutdown();
   return -1;
}