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. The default range is 0..100, and the default drawing direction is from left to right in horizontal mode and bottom to top in vertical mode. If the minimum value is greater than the maximum value, like 100..0, the drawing direction changes to the opposite direction.

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.

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  

 View on 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_screen_active());
    lv_obj_center(slider);
    lv_obj_add_event_cb(slider, slider_event_cb, LV_EVENT_VALUE_CHANGED, NULL);

    lv_obj_set_style_anim_duration(slider, 2000, 0);
    /*Create a label below the slider*/
    slider_label = lv_label_create(lv_screen_active());
    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

---

Slider with custom style

C code  

 View on 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_screen_active());
    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

---

Slider with extended drawer

C code  

 View on 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_screen_active());
    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_MAIN_END) {
        if(!lv_obj_has_state(obj, LV_STATE_PRESSED)) return;

        lv_slider_t * slider = (lv_slider_t *) obj;
        const lv_area_t * indic_area = &slider->bar.indic_area;
        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_text_get_size(&label_size, buf, LV_FONT_DEFAULT, 0, 0, LV_COORD_MAX, 0);
        lv_area_t label_area;
        label_area.x1 = 0;
        label_area.x2 = label_size.x - 1;
        label_area.y1 = 0;
        label_area.y2 = label_size.y - 1;

        lv_area_align(indic_area, &label_area, LV_ALIGN_OUT_TOP_MID, 0, -10);

        lv_draw_label_dsc_t label_draw_dsc;
        lv_draw_label_dsc_init(&label_draw_dsc);
        label_draw_dsc.color = lv_color_hex3(0x888);
        label_draw_dsc.text = buf;
        label_draw_dsc.text_local = true;
        lv_layer_t * layer = lv_event_get_layer(e);
        lv_draw_label(layer, &label_draw_dsc, &label_area);
    }
}

#endif

---

Slider with opposite direction

C code  

 View on 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;

/**
 * Slider with opposite direction
 */
void lv_example_slider_4(void)
{
    /*Create a slider in the center of the display*/
    lv_obj_t * slider = lv_slider_create(lv_screen_active());
    lv_obj_center(slider);
    lv_obj_add_event_cb(slider, slider_event_cb, LV_EVENT_VALUE_CHANGED, NULL);
    /*Reverse the direction of the slider*/
    lv_slider_set_range(slider, 100, 0);
    /*Create a label below the slider*/
    slider_label = lv_label_create(lv_screen_active());
    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

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API

lv_observer.h

lv_slider.h