Slider (lv_slider)

Overview

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

Value and range

To set an initial value use lv_slider_set_value(slider, new_value, LV_ANIM_ON/OFF). lv_slider_set_anim_time(slider, anim_time) sets the animation time in milliseconds.

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

Symmetrical

The slider can be drawn symmetrical to zero (drawn from zero, left to right), if it’s enabled with lv_slider_set_sym(slider, true)

Knob placement

The knob can be placed in two ways:

  • inside the background

  • on the edges on min/max values

Use the lv_slider_set_knob_in(slider, true/false) to choose between the modes. (knob_in = false is the default)

Styles

You can modify the slider’s styles with lv_slider_set_style(slider, LV_SLIDER_STYLE_..., &style).

  • LV_SLIDER_STYLE_BG Style of the background. All style.body properties are used. The padding values make the knob larger than the background. (negative value makes is larger)

  • LV_SLIDER_STYLE_INDIC Style of the indicator. All style.body properties are used. The padding values make the indicator smaller than the background.

  • LV_SLIDER_STYLE_KNOB Style of the knob. All style.body properties are used except padding.

Events

Besides the Generic events the following Special events are sent by the Slider:

  • LV_EVENT_VALUE_CHANGED Sent while the slider is being dragged or changed with keys.

Keys

  • LV_KEY_UP, LV_KEY_RIGHT Increment the slider’s value by 1

  • LV_KEY_DOWN, LV_KEY_LEFT Decrement the slider’s value by 1

Learn more about Keys.

Example

C

Slider with custo mstyle

Slider example in LittlevGL

code

#include "lvgl/lvgl.h"
#include <stdio.h>

static void event_handler(lv_obj_t * obj, lv_event_t event)
{
    if(event == LV_EVENT_VALUE_CHANGED) {
        printf("Value: %d\n", lv_slider_get_value(obj));
    }
}


void lv_ex_slider_1(void)
{
    /*Create styles*/
    static lv_style_t style_bg;
    static lv_style_t style_indic;
    static lv_style_t style_knob;

    lv_style_copy(&style_bg, &lv_style_pretty);
    style_bg.body.main_color =  LV_COLOR_BLACK;
    style_bg.body.grad_color =  LV_COLOR_GRAY;
    style_bg.body.radius = LV_RADIUS_CIRCLE;
    style_bg.body.border.color = LV_COLOR_WHITE;

    lv_style_copy(&style_indic, &lv_style_pretty_color);
    style_indic.body.radius = LV_RADIUS_CIRCLE;
    style_indic.body.shadow.width = 8;
    style_indic.body.shadow.color = style_indic.body.main_color;
    style_indic.body.padding.left = 3;
    style_indic.body.padding.right = 3;
    style_indic.body.padding.top = 3;
    style_indic.body.padding.bottom = 3;

    lv_style_copy(&style_knob, &lv_style_pretty);
    style_knob.body.radius = LV_RADIUS_CIRCLE;
    style_knob.body.opa = LV_OPA_70;
    style_knob.body.padding.top = 10 ;
    style_knob.body.padding.bottom = 10 ;

    /*Create a slider*/
    lv_obj_t * slider = lv_slider_create(lv_scr_act(), NULL);
    lv_slider_set_style(slider, LV_SLIDER_STYLE_BG, &style_bg);
    lv_slider_set_style(slider, LV_SLIDER_STYLE_INDIC,&style_indic);
    lv_slider_set_style(slider, LV_SLIDER_STYLE_KNOB, &style_knob);
    lv_obj_align(slider, NULL, LV_ALIGN_CENTER, 0, 0);
    lv_obj_set_event_cb(slider, event_handler);
}

Set value with slider

Set value with slider in LittlevGL

code

/**
 * @file lv_ex_slider_2.c
 *
 */

/*********************
 *      INCLUDES
 *********************/

#include "lvgl/lvgl.h"
#include <stdio.h>

/*********************
 *      DEFINES
 *********************/

/**********************
 *      TYPEDEFS
 **********************/

/**********************
 *  STATIC PROTOTYPES
 **********************/

static void slider_event_cb(lv_obj_t * slider, lv_event_t event);

/**********************
 *  STATIC VARIABLES
 **********************/

static lv_obj_t * slider_label;

/**********************
 *      MACROS
 **********************/

/**********************
 *   GLOBAL FUNCTIONS
 **********************/

void lv_ex_slider_2(void)
{
    /* Create a slider in the center of the display */
    lv_obj_t * slider = lv_slider_create(lv_scr_act(), NULL);
    lv_obj_set_width(slider, LV_DPI * 2);
    lv_obj_align(slider, NULL, LV_ALIGN_CENTER, 0, 0);
    lv_obj_set_event_cb(slider, slider_event_cb);
    lv_slider_set_range(slider, 0, 100);
    
    /* Create a label below the slider */
    slider_label = lv_label_create(lv_scr_act(), NULL);
    lv_label_set_text(slider_label, "0");
    lv_obj_set_auto_realign(slider_label, true);
    lv_obj_align(slider_label, slider, LV_ALIGN_OUT_BOTTOM_MID, 0, 10);
    
    /* Create an informative label */
    lv_obj_t * info = lv_label_create(lv_scr_act(), NULL);
    lv_label_set_text(info, "Welcome to the slider+label demo!\n"
                            "Move the slider and see that the label\n"
                            "updates to match it.");
    lv_obj_align(info, NULL, LV_ALIGN_IN_TOP_LEFT, 10, 10);
}

/**********************
 *   STATIC FUNCTIONS
 **********************/

static void slider_event_cb(lv_obj_t * slider, lv_event_t event)
{
    if(event == LV_EVENT_VALUE_CHANGED) {
        static char buf[4]; /* max 3 bytes for number plus 1 null terminating byte */
        snprintf(buf, 4, "%u", lv_slider_get_value(slider));
        lv_label_set_text(slider_label, buf);
    }
}

MicroPython

Slider with custo mstyle

Slider example in LittlevGL with MicroPython

code

def event_handler(obj, event):
    if event == lv.EVENT.VALUE_CHANGED:
        print("Value: %d" % obj.get_value())

# Create styles
style_bg = lv.style_t()
style_indic = lv.style_t()
style_knob = lv.style_t()

lv.style_copy(style_bg, lv.style_pretty)
style_bg.body.main_color =  lv.color_make(0,0,0)
style_bg.body.grad_color =  lv.color_make(0x80, 0x80, 0x80)
style_bg.body.radius = 800 # large enough to make a circle
style_bg.body.border.color = lv.color_make(0xff,0xff,0xff)

lv.style_copy(style_indic, lv.style_pretty_color)
style_indic.body.radius = 800
style_indic.body.shadow.width = 8
style_indic.body.shadow.color = style_indic.body.main_color
style_indic.body.padding.left = 3
style_indic.body.padding.right = 3
style_indic.body.padding.top = 3
style_indic.body.padding.bottom = 3

lv.style_copy(style_knob, lv.style_pretty)
style_knob.body.radius = 800
style_knob.body.opa = lv.OPA._70
style_knob.body.padding.top = 10
style_knob.body.padding.bottom = 10

# Create a slider
slider = lv.slider(lv.scr_act())
slider.set_style(lv.slider.STYLE.BG, style_bg)
slider.set_style(lv.slider.STYLE.INDIC, style_indic)
slider.set_style(lv.slider.STYLE.KNOB, style_knob)
slider.align(None, lv.ALIGN.CENTER, 0, 0)
slider.set_event_cb(event_handler)

Set value with slider

Set value with slider in LittlevGL with MicroPython

code

def slider_event_cb(slider, event):
    if event == lv.EVENT.VALUE_CHANGED:
        slider_label.set_text("%u" % slider.get_value())

# Create a slider in the center of the display
slider = lv.slider(lv.scr_act())
slider.set_width(200)
slider.align(None, lv.ALIGN.CENTER, 0, 0)
slider.set_event_cb(slider_event_cb)
slider.set_range(0, 100)

# Create a label below the slider
slider_label = lv.label(lv.scr_act())
slider_label.set_text("0")
slider_label.set_auto_realign(True)
slider_label.align(slider, lv.ALIGN.OUT_BOTTOM_MID, 0, 10)

# Create an informative label
info = lv.label(lv.scr_act())
info.set_text("""Welcome to the slider+label demo!
Move the slider and see that the label
updates to match it.""")
info.align(None, lv.ALIGN.IN_TOP_LEFT, 10, 10)

API

Typedefs

typedef uint8_t lv_slider_style_t

Enums

enum [anonymous]

Built-in styles of slider

Values:

LV_SLIDER_STYLE_BG
LV_SLIDER_STYLE_INDIC

Slider background style.

LV_SLIDER_STYLE_KNOB

Slider indicator (filled area) style.

Functions

lv_obj_t *lv_slider_create(lv_obj_t *par, const lv_obj_t *copy)

Create a slider objects

Return

pointer to the created slider

Parameters
  • par: pointer to an object, it will be the parent of the new slider

  • copy: pointer to a slider object, if not NULL then the new object will be copied from it

static void lv_slider_set_value(lv_obj_t *slider, int16_t value, lv_anim_enable_t anim)

Set a new value on the slider

Parameters
  • slider: pointer to a slider object

  • value: new value

  • anim: LV_ANIM_ON: set the value with an animation; LV_ANIM_OFF: change the value immediately

static void lv_slider_set_range(lv_obj_t *slider, int16_t min, int16_t max)

Set minimum and the maximum values of a bar

Parameters
  • slider: pointer to the slider object

  • min: minimum value

  • max: maximum value

static void lv_slider_set_anim_time(lv_obj_t *slider, uint16_t anim_time)

Make the slider symmetric to zero. The indicator will grow from zero instead of the minimum position.

Parameters
  • slider: pointer to a slider object

  • en: true: enable disable symmetric behavior; false: disable

static void lv_slider_set_sym(lv_obj_t *slider, bool en)

Set the animation time of the slider

Parameters
  • slider: pointer to a bar object

  • anim_time: the animation time in milliseconds.

void lv_slider_set_knob_in(lv_obj_t *slider, bool in)

Set the ‘knob in’ attribute of a slider

Parameters
  • slider: pointer to slider object

  • in: true: the knob is drawn always in the slider; false: the knob can be out on the edges

void lv_slider_set_style(lv_obj_t *slider, lv_slider_style_t type, const lv_style_t *style)

Set a style of a slider

Parameters
  • slider: pointer to a slider object

  • type: which style should be set

  • style: pointer to a style

int16_t lv_slider_get_value(const lv_obj_t *slider)

Get the value of a slider

Return

the value of the slider

Parameters
  • slider: pointer to a slider object

static int16_t lv_slider_get_min_value(const lv_obj_t *slider)

Get the minimum value of a slider

Return

the minimum value of the slider

Parameters
  • slider: pointer to a slider object

static int16_t lv_slider_get_max_value(const lv_obj_t *slider)

Get the maximum value of a slider

Return

the maximum value of the slider

Parameters
  • slider: pointer to a slider object

bool lv_slider_is_dragged(const lv_obj_t *slider)

Give the slider is being dragged or not

Return

true: drag in progress false: not dragged

Parameters
  • slider: pointer to a slider object

static uint16_t lv_slider_get_anim_time(lv_obj_t *slider)

Get the animation time of the slider

Return

the animation time in milliseconds.

Parameters
  • slider: pointer to a slider object

static bool lv_slider_get_sym(lv_obj_t *slider)

Get whether the slider is symmetric or not.

Return

true: symmetric is enabled; false: disable

Parameters
  • slider: pointer to a bar object

bool lv_slider_get_knob_in(const lv_obj_t *slider)

Get the ‘knob in’ attribute of a slider

Return

true: the knob is drawn always in the slider; false: the knob can be out on the edges

Parameters
  • slider: pointer to slider object

const lv_style_t *lv_slider_get_style(const lv_obj_t *slider, lv_slider_style_t type)

Get a style of a slider

Return

style pointer to a style

Parameters
  • slider: pointer to a slider object

  • type: which style should be get

struct lv_slider_ext_t

Public Members

lv_bar_ext_t bar
const lv_style_t *style_knob
int16_t drag_value
uint8_t knob_in