This is probably the most complex example of elementary Elm_Genlist. We create a tree of items, using the subitems properties of the items, and keep it in memory to be able to expand/hide subitems of an item. The full source code can be found at genlist_example_05.c

The main point is the way that Genlist manages subitems. Clicking on an item's button to expand it won't really show its children. It will only generate the "expand,request" signal, and the expansion must be done manually.

In this example we want to be able to add items as subitems of another item. If an item has any child, it must be displayed using a parent class, otherwise it will use the normal item class.

It will be possible to delete items too. Once a tree is constructed (with subitems of subitems), and the user clicks on the first parent (root of the tree), the entire subtree must be hidden. However, just calling elm_genlist_item_expanded_set(item, EINA_FALSE) won't hide them. The only thing that happens is that the parent item will change its appearance to represent that it's contracted. And the signal "contracted" will be emitted from the genlist. Thus, we must call elm_genlist_item_subitems_clear() to delete all its subitems, but still keep a way to recreate them when expanding the parent again. That's why we are going to keep a node struct for each item, that will be the data of the item, with the following information:

typedef struct _Node_Data {
     Eina_List *children;
     int value;
     int level;
     Eina_Bool favorite;
} Node_Data;

This Node_Data contains the value for the item, a number indicating its level under the tree, a list of children (to be able to expand it later) and a boolean indicating if it's a favorite item or not.

We use 3 different item classes in this example:

One for items that don't have children:

static int nitems = 0;

static char *
_item_label_get(void *data, Evas_Object *obj EINA_UNUSED, const char *part)
{
   char buf[256] = {0};
   Node_Data *d = data;

   if (!strcmp(part, "elm.text"))
     snprintf(buf, sizeof(buf), "Item # %i (level %i)", d->value, d->level);

   return strdup(buf);
}

One for items that have children:

static char *
_parent_label_get(void *data, Evas_Object *obj EINA_UNUSED, const char *part EINA_UNUSED)
{
   char buf[256];
   Node_Data *d = data;

   snprintf(buf, sizeof(buf), "Group %d (%d items)", d->value / 7,
            eina_list_count(d->children));

   return strdup(buf);
}

static Evas_Object *
_parent_content_get(void *data EINA_UNUSED, Evas_Object *obj, const char *part)
{
   Evas_Object *ic = elm_icon_add(obj);

   if (!strcmp(part, "elm.swallow.icon"))
     elm_icon_standard_set(ic, "folder");

   evas_object_size_hint_aspect_set(ic, EVAS_ASPECT_CONTROL_VERTICAL, 1, 1);
   return ic;
}

And one for items that were favorited:

static char *
_favorite_label_get(void *data, Evas_Object *obj EINA_UNUSED, const char *part)
{
   char buf[256] = {0};
   Node_Data *d = data;

   if (!strcmp(part, "elm.text"))
     snprintf(buf, sizeof(buf), "Favorite # %i", d->value);

   return strdup(buf);
}

The favorite item class is there just to demonstrate the elm_genlist_item_item_class_update() function in action. It would be much simpler to implement the favorite behavior by just changing the icon inside the icon_get functions when the favorite boolean is activated.

Now we are going to declare the callbacks for the buttons that add, delete and change items.

First, a button for appending items to the list:

static Evas_Object *
_favorite_content_get(void *data EINA_UNUSED, Evas_Object *obj, const char *part)
{
   Evas_Object *ic = elm_icon_add(obj);

   if (!strcmp(part, "elm.swallow.icon"))
     elm_icon_standard_set(ic, "apps");

   evas_object_size_hint_aspect_set(ic, EVAS_ASPECT_CONTROL_VERTICAL, 1, 1);
   return ic;
}

static void
_append_cb(void *data, Evas_Object *o EINA_UNUSED, void *event_info EINA_UNUSED)
{
   Evas_Object *list = data;
   Elm_Object_Item *glit, *parent = NULL;
   Node_Data *pdata, *d = malloc(sizeof(*d));

   d->children = NULL;
   d->value = nitems++;
   d->favorite = EINA_FALSE;

   glit = elm_genlist_selected_item_get(list);
   if (glit)
     parent = elm_genlist_item_parent_get(glit);

   if (parent)
     {
        d->level = elm_genlist_item_expanded_depth_get(parent) + 1;
        pdata = elm_object_item_data_get(parent);
        pdata->children = eina_list_append(pdata->children, d);
     }
   else
     d->level = 0;

   elm_genlist_item_append(list, _itc,
                           d, parent,
                           ELM_GENLIST_ITEM_NONE,
                           _item_sel_cb, NULL);
}

If an item is selected, a new item will be appended to the same level of that item, but using the selected item's parent as its parent too. If no item is selected, the new item will be appended to the root of the tree.

Then the callback for marking an item as favorite:

static void
_favorite_cb(void *data, Evas_Object *o EINA_UNUSED, void *event_info EINA_UNUSED)
{
   Evas_Object *list = data;
   Elm_Object_Item *glit = elm_genlist_selected_item_get(list);

   if (!glit) return;

   Node_Data *d = elm_object_item_data_get(glit);
   d->favorite = !d->favorite;
   if (d->favorite)
     elm_genlist_item_item_class_update(glit, _itfav);
   else
     {
        if (d->children)
          elm_genlist_item_item_class_update(glit, _itp);
        else
          elm_genlist_item_item_class_update(glit, _itc);
     }

   elm_genlist_item_update(glit);
}

This callback is very simple, it just changes the item class of the selected item for the "favorite" one, or go back to the "item" or "parent" class depending on that item having children or not.

Now, the most complex operation (adding a child to an item):

static void
_add_child_cb(void *data, Evas_Object *o EINA_UNUSED, void *event_info EINA_UNUSED)
{
   Evas_Object *list = data;
   Elm_Object_Item *glit = elm_genlist_selected_item_get(list);
   Elm_Object_Item *glit_prev, *glit_parent;

   if (!glit) return;

   Node_Data *d = elm_object_item_data_get(glit);
   glit_prev = elm_genlist_item_prev_get(glit);
   glit_parent = elm_genlist_item_parent_get(glit);

   Eina_Bool change_item = !d->children;

   // creating new item data
   Node_Data *ndata = malloc(sizeof(*ndata));
   ndata->value = nitems++;
   ndata->children = NULL;
   ndata->favorite = EINA_FALSE;
   ndata->level = elm_genlist_item_expanded_depth_get(glit) + 1;
   d->children = eina_list_append(d->children, ndata);

   // Changing leaf item to parent item
   if (change_item)
     {
        elm_object_item_del(glit);

        if (glit_prev != glit_parent)
          glit = elm_genlist_item_insert_after(list, _itp, d, glit_parent,
                                               glit_prev,
                                               ELM_GENLIST_ITEM_TREE,
                                               _item_sel_cb, NULL);
        else
          glit = elm_genlist_item_prepend(list, _itp, d, glit_parent,
                                          ELM_GENLIST_ITEM_TREE,
                                          _item_sel_cb, NULL);
        elm_genlist_item_expanded_set(glit, EINA_FALSE);
        elm_genlist_item_selected_set(glit, EINA_TRUE);
     }
   else if (elm_genlist_item_expanded_get(glit))
     {
        elm_genlist_item_append(list, _itc, ndata, glit,
                                ELM_GENLIST_ITEM_NONE, _item_sel_cb, NULL);
     }

   elm_genlist_item_update(glit);

}

This function gets the data of the selected item, create a new data (for the item being added), and appends it to the children list of the selected item.

Then we must check if the selected item (let's call it item1 now) to which the new item (called item2 from now on) was already a parent item too (using the parent item class) or just a normal item (using the default item class). In the first case, we just have to append the item to the end of the item1 children list.

However, if the item1 didn't have any child previously, we have to change it to a parent item now. It would be easy to just change its item class to the parent type, but there's no way to change the item flags and make it be of the type ELM_GENLIST_ITEM_TREE. Thus, we have to delete it and create a new item, and add this new item to the same position that the deleted one was. That's the reason of the checks inside the bigger if.

After adding the item to the newly converted parent, we set it to not expanded (since we don't want to show the added item immediately) and select it again, since the original item was deleted and no item is selected at the moment.

Finally, let's show the callback for deleting items:

static void
_clear_list(Node_Data *d)
{
   Node_Data *tmp;

   EINA_LIST_FREE(d->children, tmp)
      _clear_list(tmp);
   free(d);
}

static void
_del_item_cb(void *data, Evas_Object *o EINA_UNUSED, void *event_info EINA_UNUSED)
{
   Evas_Object *list = data;
   Elm_Object_Item *glit = elm_genlist_selected_item_get(list);
   Elm_Object_Item *glit_parent = NULL;

   if (!glit) return;

   Node_Data *pdata, *d = elm_object_item_data_get(glit);
   glit_parent = elm_genlist_item_parent_get(glit);
   elm_genlist_item_subitems_clear(glit);
   elm_object_item_del(glit);

   if (glit_parent)
     {
        pdata = elm_object_item_data_get(glit_parent);
        pdata->children = eina_list_remove(pdata->children, d);
     }

   _clear_list(d);

   elm_genlist_item_update(glit_parent);
}

Since we have an iternal list representing each element of our tree, once we delete an item we have to go deleting each child of that item, in our internal list. That's why we have the function _clear_list, which recursively goes freeing all the item data.

This is necessary because only when we really want to delete the item is when we need to delete the item data. When we are just contracting the item, we need to hide the children by deleting them, but keeping the item data.

Now there are two callbacks that will be called whenever the user clicks on the expand/contract icon of the item. They will just request to items to be contracted or expanded:

static void
_expand_request_cb(void *data EINA_UNUSED, Evas_Object *o EINA_UNUSED, void *event_info)
{
   Elm_Object_Item *glit = event_info;
   printf("expand request on item: %p\n", event_info);
   elm_genlist_item_expanded_set(glit, EINA_TRUE);
}

static void
_contract_request_cb(void *data EINA_UNUSED, Evas_Object *o EINA_UNUSED, void *event_info)
{
   Elm_Object_Item *glit = event_info;
   printf("contract request on item: %p\n", event_info);
   elm_genlist_item_expanded_set(glit, EINA_FALSE);
}

When the elm_genlist_item_expanded_set() function is called with EINA_TRUE, the _expanded_cb will be called. And when this happens, the subtree of that item must be recreated again. This is done using the internal list stored as item data for each item. The function code follows:

static void
_expanded_cb(void *data EINA_UNUSED, Evas_Object *o EINA_UNUSED, void *event_info)
{
   Eina_List *l;
   Elm_Object_Item *glit = event_info;
   Node_Data *it_data, *d = elm_object_item_data_get(glit);
   Evas_Object *list = elm_object_item_widget_get(glit);

   Elm_Genlist_Item_Class *ic;

   EINA_LIST_FOREACH(d->children, l, it_data)
     {
        Elm_Object_Item *nitem;
        Elm_Genlist_Item_Type type = ELM_GENLIST_ITEM_NONE;
        printf("expanding item: #%d from parent #%d\n", it_data->value, d->value);
        if (it_data->favorite)
          ic = _itfav;
        else if (it_data->children)
          {
             ic = _itp;
             type = ELM_GENLIST_ITEM_TREE;
          }

Each appended item is set to contracted, so we don't have to deal with checking if the item was contracted or expanded before its parent being contracted. It could be easily implemented, though, by adding a flag expanded inside the item data.

Now, the _contracted_cb, which is much simpler:

        else
          ic = _itc;

        nitem = elm_genlist_item_append(list, ic, it_data, glit,
                                        type, _item_sel_cb, NULL);
        elm_genlist_item_expanded_set(nitem, EINA_FALSE);
     }

We just have to call elm_genlist_item_subitems_clear(), that will take care of deleting every item, and keep the item data still stored (since we don't have any del function set on any of our item classes).

Finally, the code inside elm_main is very similar to the other examples:

elm_main(int argc EINA_UNUSED, char **argv EINA_UNUSED)
{
   Evas_Object *win, *box, *fbox;
   Evas_Object *list;
   int i;

   win = elm_win_util_standard_add("genlist", "Genlist");
   elm_policy_set(ELM_POLICY_QUIT, ELM_POLICY_QUIT_LAST_WINDOW_CLOSED);
   elm_win_autodel_set(win, EINA_TRUE);

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

   if (!_itc)
     {
        _itc = elm_genlist_item_class_new();
        _itc->item_style = "default";
        _itc->func.text_get = _item_label_get;
        _itc->func.content_get = _item_content_get;
        _itc->func.state_get = NULL;
        _itc->func.del = NULL;
     }

   if (!_itp)
     {
        _itp = elm_genlist_item_class_new();
        _itp->item_style = "default";
        _itp->func.text_get = _parent_label_get;
        _itp->func.content_get = _parent_content_get;
        _itp->func.state_get = NULL;
        _itp->func.del = NULL;
     }

   if (!_itfav)
     {
        _itfav = elm_genlist_item_class_new();
        _itfav->item_style = "default";
        _itfav->func.text_get = _favorite_label_get;
        _itfav->func.content_get = _favorite_content_get;
        _itfav->func.state_get = NULL;
        _itfav->func.del = NULL;
     }

   list = elm_genlist_add(win);

   evas_object_size_hint_weight_set(list, EVAS_HINT_EXPAND, EVAS_HINT_EXPAND);
   evas_object_size_hint_align_set(list, EVAS_HINT_FILL, EVAS_HINT_FILL);
   elm_box_pack_end(box, list);
   evas_object_show(list);

   fbox = elm_box_add(win);
   elm_box_layout_set(fbox, evas_object_box_layout_flow_horizontal,
                      NULL, NULL);
   evas_object_size_hint_weight_set(fbox, EVAS_HINT_EXPAND, 0);
   evas_object_size_hint_align_set(fbox, EVAS_HINT_FILL, EVAS_HINT_FILL);
   elm_box_pack_end(box, fbox);
   evas_object_show(fbox);

   _button_add(list, fbox, "append item", _append_cb);
   _button_add(list, fbox, "favorite", _favorite_cb);
   _button_add(list, fbox, "add child", _add_child_cb);
   _button_add(list, fbox, "del item", _del_item_cb);


   Node_Data *pdata = NULL; // data for the parent of the group
   Elm_Object_Item *glg = NULL;
   for (i = 0; i < N_ITEMS; i++)
     {
        Elm_Object_Item *gli = NULL;
        Node_Data *data = malloc(sizeof(*data)); // data for this item
        data->children = NULL;
        data->value = i;
        data->favorite = EINA_FALSE;
        nitems++;

        printf("creating item: #%d\n", data->value);
        if (i % 3 == 0)
          {
             glg = gli = elm_genlist_item_append(list, _itp, data, NULL,
                                                 ELM_GENLIST_ITEM_TREE,
                                                 _item_sel_cb, NULL);
             elm_genlist_item_expanded_set(glg, EINA_TRUE);
             pdata = data;
             data->level = 0;
          }
        else
          {
             gli = elm_genlist_item_append(list, _itc, data, glg,
                                           ELM_GENLIST_ITEM_NONE,
                                           _item_sel_cb, NULL);
             if (pdata)
               pdata->children = eina_list_append(pdata->children, data);
             data->level = 1;
          }
     }

   evas_object_smart_callback_add(list, "expand,request", _expand_request_cb, list);
   evas_object_smart_callback_add(list, "contract,request", _contract_request_cb, list);
   evas_object_smart_callback_add(list, "expanded", _expanded_cb, list);
   evas_object_smart_callback_add(list, "contracted", _contracted_cb, list);

   evas_object_resize(win, 420, 600);
   evas_object_show(win);

   elm_run();

   return 0;
}
ELM_MAIN()