acid-drop/lib/lvgl/docs/widgets/core/slider.md

.. include:: /header.rst
:github_url: |github_link_base|/widgets/core/slider.md

Slider (lv_slider)

Overview

The Slider object looks like a Bar supplemented with a knob. The knob can be dragged to set a value. Just like Bar, Slider can be vertical or horizontal.

Parts and Styles

• LV_PART_MAIN The background of the slider. Uses all the typical background style properties. padding makes the indicator smaller in the respective direction.
• LV_PART_INDICATOR The indicator that shows the current state of the slider. Also uses all the typical background style properties.
• LV_PART_KNOB A rectangle (or circle) drawn at the current value. Also uses all the typical background properties to describe the knob(s). By default, the knob is square (with an optional corner radius) with side length equal to the smaller side of the slider. The knob can be made larger with the padding values. Padding values can be asymmetric too.

Usage

Value and range

To set an initial value use lv_slider_set_value(slider, new_value, LV_ANIM_ON/OFF). The animation time is set by the styles' anim_time property.

To specify the range (min, max values), lv_slider_set_range(slider, min , max) can be used.

Modes

The slider can be one of the following modes:

• LV_SLIDER_MODE_NORMAL A normal slider as described above
• LV_SLIDER_SYMMETRICAL Draw the indicator form the zero value to current value. Requires negative minimum range and positive maximum range.
• LV_SLIDER_RANGE Allows setting the start value too by lv_bar_set_start_value(bar, new_value, LV_ANIM_ON/OFF). The start value has to be always smaller than the end value.

The mode can be changed with lv_slider_set_mode(slider, LV_SLIDER_MODE_...)

Knob-only mode

Normally, the slider can be adjusted either by dragging the knob, or by clicking on the slider bar. In the latter case the knob moves to the point clicked and slider value changes accordingly. In some cases it is desirable to set the slider to react on dragging the knob only. This feature is enabled by adding the LV_OBJ_FLAG_ADV_HITTEST: lv_obj_add_flag(slider, LV_OBJ_FLAG_ADV_HITTEST).

The extended click area (set by lv_obj_set_ext_click_area(slider, value)) increases to knob's click area.

Events

• LV_EVENT_VALUE_CHANGED Sent while the slider is being dragged or changed with keys. The event is sent continuously while the slider is dragged and once when released. Use lv_slider_is_dragged to determine whether the Slider is still being dragged or has just been released.
• LV_EVENT_DRAW_PART_BEGIN and LV_EVENT_DRAW_PART_END are sent for the following parts.
  • LV_SLIDER_DRAW_PART_KNOB The main (right) knob of the slider
    • part: LV_PART_KNOB
    • draw_area: area of the indicator
    • rect_dsc
    • id: 0
  • LV_SLIDER_DRAW_PART_KNOB The left knob of the slider
    • part: LV_PART_KNOB
    • draw_area: area of the indicator
    • rect_dsc
    • id: 1

See the events of the Bar too.

Learn more about Events.

Keys

• LV_KEY_UP/RIGHT Increment the slider's value by 1
• LV_KEY_DOWN/LEFT Decrement the slider's value by 1

Learn more about Keys.

Example

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

API

.. doxygenfile:: lv_slider.h
  :project: lvgl