The drop-down list allows the user to select one value from a list.
The drop-down list is closed by default and displays a single value or a predefined text. When activated (by click on the drop-down list), a list is created from which the user may select one option. When the user selects a new value, the list is deleted again.
The Drop-down list is added to the default group (if it is set). Besides the Drop-down list is an editable object to allow selecting an option with encoder navigation too.
The Dropdown widget is built from the elements: "button" and "list" (both not related to the button and list widgets)
- :cpp:enumerator:`LV_PART_MAIN` The background of the button. Uses the typical background properties and text properties for the text on it.
- :cpp:enumerator:`LV_PART_INDICATOR` Typically an arrow symbol that can be an image or a text (:cpp:enumerator:`LV_SYMBOL`).
The button goes to :cpp:enumerator:`LV_STATE_CHECKED` when it's opened.
- :cpp:enumerator:`LV_PART_MAIN` The list itself. Uses the typical background
properties.
max_heightcan be used to limit the height of the list. - :cpp:enumerator:`LV_PART_SCROLLBAR` The scrollbar background, border, shadow properties and width (for its own width) and right padding for the spacing on the right.
- :cpp:enumerator:`LV_PART_SELECTED` Refers to the currently pressed, checked or pressed+checked option. Also uses the typical background properties.
The list is hidden/shown on open/close. To add styles to it use :cpp:expr:`lv_dropdown_get_list(dropdown)` to get the list object. For example:
lv_obj_t * list = lv_dropdown_get_list(dropdown) /*Get the list*/
lv_obj_add_style(list, &my_style, selector) /*Add the styles to the list*/Alternatively the theme can be extended with the new styles.
Options are passed to the drop-down list as a string with
:cpp:expr:`lv_dropdown_set_options(dropdown, options)`. Options should be
separated by \n. For example: "First\nSecond\nThird". This
string will be saved in the drop-down list, so it can in a local
variable.
The :cpp:expr:`lv_dropdown_add_option(dropdown, "New option", pos)` function
inserts a new option to pos index.
To save memory the options can set from a static(constant) string too with :cpp:expr:`lv_dropdown_set_static_options(dropdown, options)`. In this case the options string should be alive while the drop-down list exists and :cpp:func:`lv_dropdown_add_option` can't be used
You can select an option manually with
:cpp:expr:`lv_dropdown_set_selected(dropdown, id)`, where id is the index of
an option.
The get the index of the selected option, use :cpp:expr:`lv_dropdown_get_selected(dropdown)`.
:cpp:expr:`lv_dropdown_get_selected_str(dropdown, buf, buf_size)` copies the
name of the selected option to buf.
The list can be created on any side. The default :cpp:enumerator:`LV_DIR_BOTTOM` can be modified by :cpp:expr:`lv_dropdown_set_dir(dropdown, LV_DIR_LEFT)` function.
If the list would be vertically out of the screen, it will be aligned to the edge.
A symbol (typically an arrow) can be added to the dropdown list with :cpp:expr:`lv_dropdown_set_symbol(dropdown, LV_SYMBOL_...)`
If the direction of the drop-down list is :cpp:enumerator:`LV_DIR_LEFT` the symbol will be shown on the left, otherwise on the right.
The main part can either show the selected option or a static text. If a
static is set with :cpp:expr:`lv_dropdown_set_text(dropdown, "Some text")` it
will be shown regardless to th selected option. If the text is NULL
the selected option is displayed on the button.
To manually open or close the drop-down list the
lv_dropdown_open/close(dropdown) function can be used.
Apart from the Generic events, the following Special events are sent by the drop-down list:
- :cpp:enumerator:`LV_EVENT_VALUE_CHANGED` Sent when the new option is selected or the list is opened/closed.
- :cpp:enumerator:`LV_EVENT_CANCEL` Sent when the list is closed
- :cpp:enumerator:`LV_EVENT_READY` Sent when the list is opened
See the events of the :ref:`Base object <lv_obj>` too.
Learn more about :ref:`events`.
LV_KEY_RIGHT/DOWNSelect the next option.LV_KEY_LEFT/UPSelect the previous option.- :cpp:enumerator:`LV_KEY_ENTER` Apply the selected option (Sends :cpp:enumerator:`LV_EVENT_VALUE_CHANGED` event and closes the drop-down list).
Learn more about :ref:`indev_keys`.