Evas smart objects events are the most widely-used type of events in graphical applications, since they are used for signals such as “clicked”, “clicked,double” (double-click), “pressed”, etc. They are identified by strings and each smart object is able to define its own events (although the names follow conventions).

• Adding a Callback on an Event: evas_object_smart_callback_add()
• Removing a Callback on an Event: evas_object_smart_callback_del()
• Examples
  • Basic Usage: Button with a Callback on the "clicked" Signal
  • Usage with evas_object_smart_callback_del(): Clicking on the Button Removes the Callback

• Smart Object Functions API

Use the evas_object_smart_callback_add() function to add a callback for an event to an object. Its prototype is

void evas_object_smart_callback_add(Evas_Object* obj,
                                    const char* event,
                                    Evas_Smart_Cb func,
                                    const void* data
                                   )

• obj a smart object
• event the event's name string
• func the callback function
• data user data to be passed to the callback function

Evas smart objects' “smart callback” has the following signature:

void (* Evas_Smart_Cb) (void *data, Evas_Object *obj, void *event_info)

The callback function definition is similar to

void some_evas_smart_cb(void *data, Evas_Object *obj, void *event_info);

• data is the same as the data which is given as the parameter to evas_object_smart_callback_add().
• obj is the object for which the event happened.
• event_info is data, which depends on the object type and event at play. The actual type is given in the documentation for the callback that is triggered

The following defines the _button_clicked() function and sets it as the callback for the clicked event of an Evas_Object (a button here).

static void
_button_clicked(void *data, Evas_Object *obj, void *event_info)
{
   // Insert function body here
}

static void
some_function(void)
{
   // Code to build the window object
   Evas_Object *button = elm_button_add(window);
   evas_object_smart_callback_add(button, "clicked", _button_clicked, NULL);
}

If some of the arguments are not used by the callback function, the compiler may raise the “unused parameter” warning. To avoid it, you can annotate the argument with the UNUSED__ macro, which is a compiler-independent way to let the compiler know that the parameter is willingly unused rather than by a mistake. <code c> void cb(void *data UNUSED__, Evas_Object *obj, void *event_info UNUSED__); </code> For a given object and event, callbacks are called in the order they have been added. The evas_object_smart_callback_add() function does not execute any special processing if it is called several times with the same callback function and/or data. Callbacks are called as many times as they have been added and in the order they have been added. ==== Removing a Callback on an Event: evas_object_smart_callback_del() ==== The evas_object_smart_callback_del() function enables deleting a callback for a signal on an object. Its prototype is <code c> void* evas_object_smart_callback_del(Evas_Object* obj, const char* event, Evas_Smart_Cb func ) </code> It removes the first match for the given event and callback and returns the data pointer that was used in the corresponding call to evas_object_smart_callback_add()''. ==== Examples ==== === Basic Usage: Button with a Callback on the “clicked” Signal === <code c> static void _button_clicked(void *data UNUSED__, Evas_Object *obj UNUSED__, void *event_info UNUSED__) { fprintf(stdout, “Button clicked.\n”); fflush(stdout); elm_exit(); } static void _add_button(Evas_Object *window) { Evas_Object *button; button = elm_button_add(window); elm_object_text_set(button, “Click Me To Exit!”); evas_object_smart_callback_add(button, “clicked”, _button_clicked, NULL); evas_object_show(button); } </code> === Usage with evas_object_smart_callback_del(): Clicking on the Button Removes the Callback === <code c> static void _button_clicked(void *data UNUSED__, Evas_Object *obj, void *event_info UNUSED__) { fprintf(stdout, “Button clicked.\n”); fflush(stdout); evas_object_smart_callback_del(obj, “clicked”, _button_clicked); } static void _add_button(Evas_Object *window) { Evas_Object *button; button = elm_button_add(window); elm_object_text_set(button, “Click Me!”); evas_object_smart_callback_add(button, “clicked”, _button_clicked, NULL); evas_object_show(button); } </code>
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