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.

Parts and Styles

The Slider's main part is called LV_SLIDER_PART_BG and it uses the typical background style properties.

LV_SLIDER_PART_INDIC is a virtual part which also uses all the typical background properties. By default, the indicator maximal size is the same as the background's size but setting positive padding values in LV_SLIDER_PART_BG will make the indicator smaller. (negative values will make it larger) If the value style property is used on the indicator the alignment will be calculated based on the current size of the indicator. For example a center aligned value is always shown in the middle of the indicator regardless it's current size.

LV_SLIDER_PART_KNOB is a virtual part using all the typical background properties to describe the knob(s). Similarly to the indicator the value text is also aligned to the current position and size of the knob. By default the knob is square (with a 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). 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 and Range

Besides the normal type the Slider can be configured in two additional types:

  • LV_SLIDER_TYPE_NORMAL normal type

  • LV_SLIDER_TYPE_SYMMETRICAL draw the indicator symmetrical to zero (drawn from zero, left to right)

  • LV_SLIDER_TYPE_RANGE allow the use of an additional knob for the left (start) value. (Can be used with lv_slider_set/get_left_value())

The type can be changed with lv_slider_set_type(slider, LV_SLIDER_TYPE_...)

Knob-only mode

Normally, the slider can be adjusted either by dragging the knob, or 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 calling lv_obj_set_adv_hittest(slider, true);.

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. The event is sent continuously while the slider is dragged and only when it is released. Use lv_slider_is_dragged to decide whether is slider is being dragged or just released.

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 custom style

code

#include "../../../lv_examples.h"
#include <stdio.h>
#if LV_USE_SLIDER

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 a slider*/
    lv_obj_t * slider = lv_slider_create(lv_scr_act(), NULL);
    lv_obj_align(slider, NULL, LV_ALIGN_CENTER, 0, 0);
    lv_obj_set_event_cb(slider, event_handler);
}

#endif

Set value with slider

code

#include "../../../lv_examples.h"
#include <stdio.h>
#if LV_USE_SLIDER

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

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 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);
    }
}

#endif

MicroPython

No examples yet.

API

Typedefs

typedef uint8_t lv_slider_type_t

Enums

enum [anonymous]

Values:

enumerator LV_SLIDER_TYPE_NORMAL
enumerator LV_SLIDER_TYPE_SYMMETRICAL
enumerator LV_SLIDER_TYPE_RANGE
enum [anonymous]

Built-in styles of slider

Values:

enumerator LV_SLIDER_PART_BG
enumerator LV_SLIDER_PART_INDIC

Slider background style.

enumerator LV_SLIDER_PART_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

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

void lv_slider_set_left_value(lv_obj_t *slider, int16_t left_value, lv_anim_enable_t anim)

Set a new value for the left knob of a slider

Parameters
  • slider: pointer to a slider object

  • left_value: new value

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

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

void lv_slider_set_anim_time(lv_obj_t *slider, uint16_t anim_time)

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_type(lv_obj_t *slider, lv_slider_type_t type)

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

int16_t lv_slider_get_value(const lv_obj_t *slider)

Get the value of the main knob of a slider

Return

the value of the main knob of the slider

Parameters
  • slider: pointer to a slider object

int16_t lv_slider_get_left_value(const lv_obj_t *slider)

Get the value of the left knob of a slider

Return

the value of the left knob of the slider

Parameters
  • slider: pointer to a slider object

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

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

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

lv_slider_type_t lv_slider_get_type(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

struct lv_slider_ext_t

Public Members

lv_bar_ext_t bar
lv_style_list_t style_knob
lv_area_t left_knob_area
lv_area_t right_knob_area
int16_t *value_to_set
uint8_t dragging