lvgl/docs/widgets/core/dropdown.md

.. include:: /header.rst 
:github_url: |github_link_base|/widgets/dropdown.md

Drop-down list (lv_dropdown)

Overview

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.

The Drop-down list is added to the deafult group (if it is set). Besides the Drop-down list is an editable object to allow selecting an option with encoder navigation too.

Parts and Styles

The Dropdown widgets is built from the elements: a "button" and a "list" (they are not realted to the butto and list widgets)

Button

• LV_PART_MAIN The background of the button. It uses the typicaly background proeprties and text proeprties for the text on it.
• LV_PART_INDICATOR Typically an arrow symbol that can be an image or a text (LV_SYMBOL).

The button goes to LV_STATE_CHECKED when its opened.

List

• LV_PART_MAIN The list itself and it uses the typical background proeprties. max_height can be used to limit the height of the list.
• LV_PART_SCROLLBAR The scrollbar the background, border, shadow properties and width (for its width) and right padding for the spacing on the right.
• LV_PART_SELECTED Refers to the currently pressed, checked or prssed+checked option. It also uses the typical background properties.

As the list not exists when the drop-down list is closed it's not possible to simply add styles to it. Instead the following should be done:

1. Ad an event handler to the button for LV_EVENT_VALUE_CHANGED (triggered when the list is opened/closed)
2. Use lv_obj_t * list = lv_dropdown_get_list(dropdown)
3. if(list != NULL) {/*Add the styles to the list*/}

Alternatively the the theme can be extended with the new styles.

Usage

Overview

Set options

The options are passed to the drop-down list as a string with lv_dropdown_set_options(dropdown, options). The options should be separated by \n. For example: "First\nSecond\nThird". The string will be saved in the drop-down list, so it can in local variable too.

The 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 lv_dropdown_set_static_options(dropdown, options). In this case the options string should be alive while the drop-down list exists and lv_dropdown_add_option can't be used

You can select an option manually with lv_dropdown_set_selected(dropdown, id), where id is the index of an option.

Get selected option

The get the currently selected option, use lv_dropdown_get_selected(dropdown). It will return the index of the selected option.

lv_dropdown_get_selected_str(dropdown, buf, buf_size) copies the name of the selected option to a buf.

Direction

The list can be created on any side. The default LV_DIR_BOTTOM can be modified by lv_dropdown_set_dir(dropdown, LV_DIR_LEFT/RIGHT/UP/BOTTOM) function.

If the list would be vertically out of the screen, it will aligned to the edge.

Symbol

A symbol (typically an arrow) can be added to the drop down list with lv_dropdown_set_symbol(dropdown, LV_SYMBOL_...)

If the direction of the drop-down list is LV_DIR_LEFT the symbol will be shown on the left, else on the right.

Show selected

The main part can either show the selected option or a static text. If a static is set with lv_dropdown_set_text(dropdown, "Some text") it will be shown regardless to th selected option. Id the text text is NULL the selected option is displayed on the button.

Manually open/close

To manually open or close the drop-down list the lv_dropdown_open/close(dropdown) function can be used.

Events

Besides the Generic events, the following Special events are sent by the drop-down list:

• LV_EVENT_VALUE_CHANGED Sent when the new option is selected or the list is opened/closed.

Learn more about Events.

Keys

• LV_KEY_RIGHT/DOWN Select the next option.
• LV_KEY_LEFT/UP Select the previous option.
• LY_KEY_ENTER Apply the selected option (Send LV_EVENT_VALUE_CHANGED event and close the drop-down list).

Learn more about Keys.

Example

.. include:: ../../../examples/widgets/dropdown/index.rst

API

.. doxygenfile:: lv_dropdown.h
  :project: lvgl