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libraries/lvgl/docs/widgets/core/roller.md

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+# Roller (lv_roller)
+
+## Overview
+
+Roller allows you to simply select one option from a list by scrolling.
+
+## Parts and Styles
+- `LV_PART_MAIN` The background of the roller uses all the typical background properties and text style properties. `style_text_line_space` adjusts the space between the options.
+When the Roller is scrolled and doesn't stop exactly on an option it will scroll to the nearest valid option automatically in `anim_time` milliseconds as specified in the style.
+- `LV_PART_SELECTED` The selected option in the middle. Besides the typical background properties it uses the text style properties to change the appearance of the text in the selected area.
+
+## Usage
+
+### Set options
+Options are passed to the Roller as a string with `lv_roller_set_options(roller, options, LV_ROLLER_MODE_NORMAL/INFINITE)`. The options should be separated by `\n`. For example: `"First\nSecond\nThird"`.
+
+`LV_ROLLER_MODE_INFINITE` makes the roller circular.
+
+You can select an option manually with `lv_roller_set_selected(roller, id, LV_ANIM_ON/OFF)`, where *id* is the index of an option.
+
+### Get selected option
+To get the *index* of the currently selected option use `lv_roller_get_selected(roller)`.
+
+`lv_roller_get_selected_str(roller, buf, buf_size)` will copy the name of the selected option to `buf`.
+
+### Visible rows
+The number of visible rows can be adjusted with `lv_roller_set_visible_row_count(roller, num)`.
+
+This function calculates the height with the current style. If the font, line space, border width, etc. of the roller changes this function needs to be called again.
+
+## Events
+- `LV_EVENT_VALUE_CHANGED` Sent when a new option is selected.
+
+See the events of the [Base object](/widgets/obj) too.
+
+Learn more about [Events](/overview/event).
+
+## 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)
+
+## Example
+
+```eval_rst
+
+.. include:: ../../../examples/widgets/roller/index.rst
+
+```
+
+## API
+
+```eval_rst
+
+.. doxygenfile:: lv_roller.h
+  :project: lvgl
+
+```