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 being dragged.

  • LV_EVENT_RELEASED Sent when the slider 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

Simple Slider

C code  

 GitHub
#include "../../lv_examples.h"
#if LV_USE_SLIDER && LV_BUILD_EXAMPLES

static void slider_event_cb(lv_event_t * e);
static lv_obj_t * slider_label;

/**
 * A default slider with a label displaying the current value
 */
void lv_example_slider_1(void)
{
    /*Create a slider in the center of the display*/
    lv_obj_t * slider = lv_slider_create(lv_scr_act());
    lv_obj_center(slider);
    lv_obj_add_event_cb(slider, slider_event_cb, LV_EVENT_VALUE_CHANGED, NULL);

    /*Create a label below the slider*/
    slider_label = lv_label_create(lv_scr_act());
    lv_label_set_text(slider_label, "0%");

    lv_obj_align_to(slider_label, slider, LV_ALIGN_OUT_BOTTOM_MID, 0, 10);
}

static void slider_event_cb(lv_event_t * e)
{
    lv_obj_t * slider = lv_event_get_target(e);
    char buf[8];
    lv_snprintf(buf, sizeof(buf), "%d%%", (int)lv_slider_get_value(slider));
    lv_label_set_text(slider_label, buf);
    lv_obj_align_to(slider_label, slider, LV_ALIGN_OUT_BOTTOM_MID, 0, 10);
}

#endif

MicroPython code  

 GitHub Simulator
#
# A default slider with a label displaying the current value
#
def slider_event_cb(e):

    slider = e.get_target()
    slider_label.set_text("{:d}%".format(slider.get_value()))
    slider_label.align_to(slider, lv.ALIGN.OUT_BOTTOM_MID, 0, 10)

# Create a slider in the center of the display
slider = lv.slider(lv.scr_act())
slider.center()
slider.add_event_cb(slider_event_cb, lv.EVENT.VALUE_CHANGED, None)

# Create a label below the slider
slider_label = lv.label(lv.scr_act())
slider_label.set_text("0%")

slider_label.align_to(slider, lv.ALIGN.OUT_BOTTOM_MID, 0, 10)

Slider with custom style

C code  

 GitHub
#include "../../lv_examples.h"
#if LV_USE_SLIDER && LV_BUILD_EXAMPLES

/**
 * Show how to style a slider.
 */
void lv_example_slider_2(void)
{
    /*Create a transition*/
    static const lv_style_prop_t props[] = {LV_STYLE_BG_COLOR, 0};
    static lv_style_transition_dsc_t transition_dsc;
    lv_style_transition_dsc_init(&transition_dsc, props, lv_anim_path_linear, 300, 0, NULL);

    static lv_style_t style_main;
    static lv_style_t style_indicator;
    static lv_style_t style_knob;
    static lv_style_t style_pressed_color;
    lv_style_init(&style_main);
    lv_style_set_bg_opa(&style_main, LV_OPA_COVER);
    lv_style_set_bg_color(&style_main, lv_color_hex3(0xbbb));
    lv_style_set_radius(&style_main, LV_RADIUS_CIRCLE);
    lv_style_set_pad_ver(&style_main, -2); /*Makes the indicator larger*/

    lv_style_init(&style_indicator);
    lv_style_set_bg_opa(&style_indicator, LV_OPA_COVER);
    lv_style_set_bg_color(&style_indicator, lv_palette_main(LV_PALETTE_CYAN));
    lv_style_set_radius(&style_indicator, LV_RADIUS_CIRCLE);
    lv_style_set_transition(&style_indicator, &transition_dsc);

    lv_style_init(&style_knob);
    lv_style_set_bg_opa(&style_knob, LV_OPA_COVER);
    lv_style_set_bg_color(&style_knob, lv_palette_main(LV_PALETTE_CYAN));
    lv_style_set_border_color(&style_knob, lv_palette_darken(LV_PALETTE_CYAN, 3));
    lv_style_set_border_width(&style_knob, 2);
    lv_style_set_radius(&style_knob, LV_RADIUS_CIRCLE);
    lv_style_set_pad_all(&style_knob, 6); /*Makes the knob larger*/
    lv_style_set_transition(&style_knob, &transition_dsc);

    lv_style_init(&style_pressed_color);
    lv_style_set_bg_color(&style_pressed_color, lv_palette_darken(LV_PALETTE_CYAN, 2));

    /*Create a slider and add the style*/
    lv_obj_t * slider = lv_slider_create(lv_scr_act());
    lv_obj_remove_style_all(slider);        /*Remove the styles coming from the theme*/

    lv_obj_add_style(slider, &style_main, LV_PART_MAIN);
    lv_obj_add_style(slider, &style_indicator, LV_PART_INDICATOR);
    lv_obj_add_style(slider, &style_pressed_color, LV_PART_INDICATOR | LV_STATE_PRESSED);
    lv_obj_add_style(slider, &style_knob, LV_PART_KNOB);
    lv_obj_add_style(slider, &style_pressed_color, LV_PART_KNOB | LV_STATE_PRESSED);

    lv_obj_center(slider);
}

#endif

MicroPython code  

 GitHub Simulator
#
# Show how to style a slider.
#
# Create a transition
props = [lv.STYLE.BG_COLOR, 0]
transition_dsc = lv.style_transition_dsc_t()
transition_dsc.init(props, lv.anim_t.path_linear, 300, 0, None)

style_main = lv.style_t()
style_indicator = lv.style_t()
style_knob = lv.style_t()
style_pressed_color = lv.style_t()
style_main.init()
style_main.set_bg_opa(lv.OPA.COVER)
style_main.set_bg_color(lv.color_hex3(0xbbb))
style_main.set_radius(lv.RADIUS.CIRCLE)
style_main.set_pad_ver(-2)                 # Makes the indicator larger

style_indicator.init()
style_indicator.set_bg_opa(lv.OPA.COVER)
style_indicator.set_bg_color(lv.palette_main(lv.PALETTE.CYAN))
style_indicator.set_radius(lv.RADIUS.CIRCLE)
style_indicator.set_transition(transition_dsc)

style_knob.init()
style_knob.set_bg_opa(lv.OPA.COVER)
style_knob.set_bg_color(lv.palette_main(lv.PALETTE.CYAN))
style_knob.set_border_color(lv.palette_darken(lv.PALETTE.CYAN, 3))
style_knob.set_border_width(2)
style_knob.set_radius(lv.RADIUS.CIRCLE)
style_knob.set_pad_all(6)                   # Makes the knob larger
style_knob.set_transition(transition_dsc)

style_pressed_color.init()
style_pressed_color.set_bg_color(lv.palette_darken(lv.PALETTE.CYAN, 2))

# Create a slider and add the style
slider = lv.slider(lv.scr_act())
slider.remove_style_all()                   # Remove the styles coming from the theme

slider.add_style(style_main, lv.PART.MAIN)
slider.add_style(style_indicator, lv.PART.INDICATOR)
slider.add_style(style_pressed_color, lv.PART.INDICATOR | lv.STATE.PRESSED)
slider.add_style(style_knob, lv.PART.KNOB)
slider.add_style(style_pressed_color, lv.PART.KNOB | lv.STATE.PRESSED)

slider.center()

Slider with extended drawer

C code  

 GitHub
#include "../../lv_examples.h"
#if LV_USE_SLIDER && LV_BUILD_EXAMPLES

static void slider_event_cb(lv_event_t * e);

/**
 * Show the current value when the slider is pressed by extending the drawer
 *
 */
void lv_example_slider_3(void)
{
    /*Create a slider in the center of the display*/
    lv_obj_t * slider;
    slider = lv_slider_create(lv_scr_act());
    lv_obj_center(slider);

    lv_slider_set_mode(slider, LV_SLIDER_MODE_RANGE);
    lv_slider_set_value(slider, 70, LV_ANIM_OFF);
    lv_slider_set_left_value(slider, 20, LV_ANIM_OFF);

    lv_obj_add_event_cb(slider, slider_event_cb, LV_EVENT_ALL, NULL);
    lv_obj_refresh_ext_draw_size(slider);
}

static void slider_event_cb(lv_event_t * e)
{
    lv_event_code_t code = lv_event_get_code(e);
    lv_obj_t * obj = lv_event_get_target(e);

    /*Provide some extra space for the value*/
    if(code == LV_EVENT_REFR_EXT_DRAW_SIZE) {
        lv_event_set_ext_draw_size(e, 50);
    }
    else if(code == LV_EVENT_DRAW_PART_END) {
        lv_obj_draw_part_dsc_t * dsc = lv_event_get_draw_part_dsc(e);
        if(dsc->part == LV_PART_INDICATOR) {
            char buf[16];
            lv_snprintf(buf, sizeof(buf), "%d - %d", (int)lv_slider_get_left_value(obj), (int)lv_slider_get_value(obj));

            lv_point_t label_size;
            lv_txt_get_size(&label_size, buf, LV_FONT_DEFAULT, 0, 0, LV_COORD_MAX, 0);
            lv_area_t label_area;
            label_area.x1 = dsc->draw_area->x1 + lv_area_get_width(dsc->draw_area) / 2 - label_size.x / 2;
            label_area.x2 = label_area.x1 + label_size.x;
            label_area.y2 = dsc->draw_area->y1 - 10;
            label_area.y1 = label_area.y2 - label_size.y;

            lv_draw_label_dsc_t label_draw_dsc;
            lv_draw_label_dsc_init(&label_draw_dsc);
            label_draw_dsc.color = lv_color_hex3(0x888);
            lv_draw_label(dsc->draw_ctx, &label_draw_dsc, &label_area, buf, NULL);
        }
    }
}

#endif

MicroPython code  

 GitHub Simulator
def slider_event_cb(e):
    code = e.get_code()
    obj = e.get_target()

    # Provide some extra space for the value
    if code == lv.EVENT.REFR_EXT_DRAW_SIZE:
        e.set_ext_draw_size(50)

    elif code == lv.EVENT.DRAW_PART_END:
        # print("DRAW_PART_END")
        dsc = lv.obj_draw_part_dsc_t.__cast__(e.get_param())
        # print(dsc)
        if dsc.part == lv.PART.INDICATOR:
            label_text = "{:d} - {:d}".format(obj.get_left_value(),slider.get_value())
            label_size = lv.point_t()
            lv.txt_get_size(label_size, label_text, lv.font_default(), 0, 0, lv.COORD.MAX, 0)
            # print(label_size.x,label_size.y)
            label_area = lv.area_t()
            label_area.x1 = dsc.draw_area.x1 + dsc.draw_area.get_width() // 2 - label_size.x // 2
            label_area.x2 = label_area.x1 + label_size.x
            label_area.y2 = dsc.draw_area.y1 - 10
            label_area.y1 = label_area.y2 - label_size.y

            label_draw_dsc = lv.draw_label_dsc_t()
            label_draw_dsc.init()

            dsc.draw_ctx.label(label_draw_dsc, label_area, label_text, None)
#
# Show the current value when the slider if pressed by extending the drawer
#
#
#Create a slider in the center of the display

slider = lv.slider(lv.scr_act())
slider.center()

slider.set_mode(lv.slider.MODE.RANGE)
slider.set_value(70, lv.ANIM.OFF)
slider.set_left_value(20, lv.ANIM.OFF)

slider.add_event_cb(slider_event_cb, lv.EVENT.ALL, None)
slider.refresh_ext_draw_size()

API

Typedefs

typedef uint8_t lv_slider_mode_t

Enums

enum [anonymous]

Values:

enumerator LV_SLIDER_MODE_NORMAL
enumerator LV_SLIDER_MODE_SYMMETRICAL
enumerator LV_SLIDER_MODE_RANGE
enum lv_slider_draw_part_type_t

type field in lv_obj_draw_part_dsc_t if class_p = lv_slider_class Used in LV_EVENT_DRAW_PART_BEGIN and LV_EVENT_DRAW_PART_END

Values:

enumerator LV_SLIDER_DRAW_PART_KNOB

The main (right) knob's rectangle

enumerator LV_SLIDER_DRAW_PART_KNOB_LEFT

The left knob's rectangle

Functions

lv_obj_t *lv_slider_create(lv_obj_t *parent)

Create a slider object

Parameters

parent -- pointer to an object, it will be the parent of the new slider.

Returns

pointer to the created slider

static inline void lv_slider_set_value(lv_obj_t *obj, int32_t value, lv_anim_enable_t anim)

Set a new value on the slider

Parameters

  • obj -- pointer to a slider object

  • value -- the new value

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

static inline void lv_slider_set_left_value(lv_obj_t *obj, int32_t value, lv_anim_enable_t anim)

Set a new value for the left knob of a slider

Parameters

  • obj -- 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 inline void lv_slider_set_range(lv_obj_t *obj, int32_t min, int32_t max)

Set minimum and the maximum values of a bar

Parameters

  • obj -- pointer to the slider object

  • min -- minimum value

  • max -- maximum value

static inline void lv_slider_set_mode(lv_obj_t *obj, lv_slider_mode_t mode)

Set the mode of slider.

Parameters

  • obj -- pointer to a slider object

  • mode -- the mode of the slider. See ::lv_slider_mode_t

static inline int32_t lv_slider_get_value(const lv_obj_t *obj)

Get the value of the main knob of a slider

Parameters

obj -- pointer to a slider object

Returns

the value of the main knob of the slider

static inline int32_t lv_slider_get_left_value(const lv_obj_t *obj)

Get the value of the left knob of a slider

Parameters

obj -- pointer to a slider object

Returns

the value of the left knob of the slider

static inline int32_t lv_slider_get_min_value(const lv_obj_t *obj)

Get the minimum value of a slider

Parameters

obj -- pointer to a slider object

Returns

the minimum value of the slider

static inline int32_t lv_slider_get_max_value(const lv_obj_t *obj)

Get the maximum value of a slider

Parameters

obj -- pointer to a slider object

Returns

the maximum value of the slider

bool lv_slider_is_dragged(const lv_obj_t *obj)

Give the slider is being dragged or not

Parameters

obj -- pointer to a slider object

Returns

true: drag in progress false: not dragged

static inline lv_slider_mode_t lv_slider_get_mode(lv_obj_t *slider)

Get the mode of the slider.

Parameters

obj -- pointer to a bar object

Returns

see ::lv_slider_mode_t

Variables

const lv_obj_class_t lv_slider_class
struct lv_slider_t

Public Members

lv_bar_t bar
lv_area_t left_knob_area
lv_area_t right_knob_area
int32_t *value_to_set
uint8_t dragging
uint8_t left_knob_focus